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R127 817 MEASURED CHARACTERISTICS OF MULTI-GAP LOOP AND 1/2 ASYMPTOTIC CONICAL DIPOLE..(U) MICHIGAN UNIY ANN ARBOR V V LIEPA ET AL. MAR 83 t786-i-F AFWL-TR-82-82 UNCLASSIFIED F2968i-78-C-6882 F/G 9/i NL smhhhhlohll EhhmhhhhhhllI l/ll/llllllllE EIIIIIIIIIIII EIIIhIIIIhIIIE lllllllflflll.l
Transcript
Page 1: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

R127 817 MEASURED CHARACTERISTICS OF MULTI-GAP LOOP AND 1/2ASYMPTOTIC CONICAL DIPOLE..(U) MICHIGAN UNIY ANN ARBORV V LIEPA ET AL. MAR 83 t786-i-F AFWL-TR-82-82

UNCLASSIFIED F2968i-78-C-6882 F/G 9/i NL

smhhhhlohllEhhmhhhhhhllIl/ll/llllllllEEIIIIIIIIIIIIEIIIhIIIIhIIIElllllllflflll.l

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*L 6

. . .. . . . . . . . . . . . . . . . . . . .

m

I 2

ilIuilna

1.25m

MICROCOPY RESOLUTION TEST CHARTNATIONAL BUREAU OF STANDARDS-1963-A

_ _ __'

_ _ _ _1

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. . . . . .

AFWL-TR-82-82 AFWL-TR-*82-82

MEASURED CHARACTERISTICS OF MULTI-GAP* LOOP AND ASYMPTOTIC CONICAL DIPOLE

ELECTROMAGNETIC FIELD SENSORS

iV. V. LiepaT. B. A. Senior

The University of MichiganINO Ann Arbor MI 48109

"* March 1983

'14 Final Report , )T. C5 (M A*Y 19830

' Approved for public release; distribution unlimited.

r4.°.

IJ AIR FORCE WEAPONS LABORATORYAir Force Systems CommandKirtland Air Force Base, NM 87117

,8 05 u6-009

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AFWL-TR-82-82

This final report was prepared by the University of Michigan, Ann Arbor,Michigan, under Contract F29601-78-C-0082, Job Order 37630132 with the AirForce Weapons Laboratory, Kirtland Air Force Base, New Mexico. Mr. William D.Prather (NTAA) was the Laboratory Project Officer-in-Charge.

When Government drawings, specifications, or other data are used for anypurpose other than in connection with a definitely Government-related procure-ment, the United States Government incurs no responsibility or any obligationwhatsoever. The fact that the Government may have formulated or in any waysupplied the said drawings, specifications, or other data, is not to beregarded by implication, or otherwise in any manner construed, as licensingthe holder, or any other person or corporation; or as conveying any rightsor permission to manufacture, use, or sell any patented invention that mayin any way be related thereto.

This report has been authored by a contractor of the United StatesGovernment. Accordingly, the United States Government retains a nonexclusive,royalty-free license to publish or reproduce the material contained herein,or allow others to do so, for the United States Government purposes.

This report has been reviewed by the Public Affairs Office and isreleasable to the National Technical Information Service (NTIS). At NTIS,it will be available to the general public, including foreign nations.

If your address has changed, if you wish to be removed from our mailinglist, or if your organization no longer em~ioys the addressee, please notifyAFWL/NTAA, Kirtland AFB, NM 87117 to help us maintain a current mailing list.

This technical report has been reviewed and is approved for publication.

WILLIAM D. PRATHERProject Officer

FOR THE COMMANDER

DAVID W. GARRISON RO CASE, JR.Lt Colonel, USAF Lt Colonel, USAFChief, Applications Branch Chief, Aircraft & Missiles Division

* DO NOT RETURN COPIES OF THIS REPORT UNLESS CONTRACTUAL OBLIGATIONS OR NOTICEON A SPECIFIC DOCUMENT REQUIRES THAT IT BE RETURNED.

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-- -- . .. .7

UNCLASSI FIEDSECURITY CLASSIFICATION OF THIS PAGE (Mhn Date Entered)

PAGE READ INSTRUCTIONSREPORT DOCUMENTATION PBEFORE COMPLETING FORM

. REPORT NUMBER 2.GOVT ACESSIUtiO. 3. RECIPIENT'S CATALOG NUMBER

AFWL-TR-82-82 __ _

4. TITLE (and Subtitle) 5. TYPE OF REPORT & PERIOD COVERED

MEASURED'CHARACTERISTICS OF MULTI-CAP LOOP AND Final ReportASYMPTOTIC CONICAL DIPOLE ELECTROMAGNETIC FIELDSENSORS S. PERFORMING ORG. REPORT NUMBER

017816-1-F, EMPTD-6-UM-0017. AUTHOR(@) S. CONTRACTOR GRANT NUMUER(s)

V. V. LiepaT. B. A. Senior F29601-78-C-0082

S. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT, PROJECT, TASK

AREA & WORK UNIT NUMBERS

The University of MichiganAnn Arbor, MI 48109 64711 F/37630132

II. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATEMarch 1983

Air Force Weapons Laboratory (NTAA) 13. NUMBER OF PAGESKirtland Air Force Base, NM 87117 158

14. MONITORING AGENCY NAME & ADDRESS(if different from Controlling Olfie) IS. SECURITY CLASS. (of this report)

UnclassifiedISs. DECL ASSI FIC ATION/ DOWN GRADING

SCHEDULE

16. DISTRIBUTION STATEMENT (of thls Report)

Approved for public release; distribution unlimited.

17. DISTRIBUTION STATEMENT (of the abstract entered In Block 20, It difierent from Report)

II. SUPPLEMENTARY NOTES

IS. KEY WORDS (Continua on reverse side If necessary and Identify by block number)

Asymptotic Conical Dipole (ACD)Multi-Gap Loop (MGL)Electromagnetic FieldCal IbrationSensors

_ 0. ABSTRACT (Continue on reverse aid* it necessar aind identify by block number)

The frequency responses of the MGL-2D(a), MGL-6A(A) and ACD-4A(R) free-spacesensors have been measured and analyzed. The measurements were made over thefrequency range 118 to 4400 MHz whose upper limit far exceeds the 3-dB roll-offfrequencies for the sensors. All three sensors were evaluated in terms of thelinearity of the frequency response, the angular behavior vis-a-vis a dipolepattern, and the rotational symmetry (MGL sensors only). Whereas the linearitypersists only slightly beyond the roll-off frequencies, the dipole and symmetry

(Ovpr)

DDIj 1473 EDITION OF I NOV 65IS OBSOLETEDSR JAN IY UNCLASSIFIEDSECURITY CL.ASSIFICATION OF THIS PACE (*len Datem Entered)

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UNCLASSIFIEDSECURITY CLASSIFICATION OF THIS PAOE(Whan Daea Entered)

20. ABSTRACT (Continued)

properties extend to frequencies two or three times greater.

U In addition, some preliminary data for the MGL-58(R) and MGL-7A(R) groundplane sensors are presented.

UNCLASSIFIEDSECURITY CLASSIFICATION OF THIS PAGIEr(b~f Date Entered)

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L'4. ACKNOWLEDGEMENT

The authors are indebted to H. Yoon, of the University of Michigan, for

making the measurements, sometimes two or three times over; to C. Bickley

and T. M. Willis, III, of the University of Michigan, for developing the data

processing techniques and writing the programs; and to W. Rasey for typing

the manuscript. We are especially grateful to Dr. C. Baum of the Air Force

Weapons Laboratory for his suggestions in the area of data analysis and

presentation.

Aecoss21of ForIITIS QrA&I1

Dtic U" 1

D1istibuition

i.

.-... . - - - - - - - - - - - - - -

i. :Dist~u specia

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.. .

TABLE OF CONTENTS

Section Page

1. INTRODUCTION 1

2. GENERAL FORMULAS 3

2.1 Theoretical Considerations 32.2 Practical Considerations 8

3. EXPERIMENTAL FACILITY 12

4. GROUND PLANE SENSOR EVALUATION 16

4.1 Ground Plane 164.2 Measurements and Calibrations 174.3 Sensor Responses 274.4 Discussion 35

5. FREE-SPACE SENSOR EVALUATION 46

5.1 The Sensors 465.2 Experimental Techniques 495.3 Angular Response Measurements 54

5.3.1 ACD-4A(R) Sensor 545.3.2 MGL-2D(A) and MGL-6D(A) 56

5.4 Angular Response Data Analysis 595.5 Frequency Response Data Analysis 81

6. SUMMARY 87

REFERENCES 90

APPENDIX A: ACD-4A(R) DIPOLE RESPONSE DATA (RAW) 91

APPENDIX B: MGL-2D(A) AND MGL-6A(A) DIPOLE RESPONSE DATA (RAW) 107

APPENDIX C: MGL-2D(A) AND MGL-6A(A) ROTATIONAL RESPONSEDATA (RAW) 136

" ill

- " : . - . . . .- .- _ , . -.. . , -, ,-. --. . .. . . . .. ._ _ __ _ _ _ _. _.. ..__ .. ..

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ILLUSTRATIONS

Figure Page

I Coordinate systems used for theoretical analysis. 6

2 Block diagram of the facility. 13

3 Resistively loaded ground plane used in themeasurements. 18

4 Ground plane sensors used in the evaluation. 20

5 Calibration of the 20-dB attenuator, deduced frommeasurements numbers 5 and 7. 24

6 Calibration of the 6-dB attenuator, deduced frommeasurements numbers 6 and 7. 25

7 Calibration for the 0.020-inch coax, deduced frommeasurements numbers 9 and 10. 26

8 Computed calibration for the 0.020-inch coax. 28

9 Calibration for the 0.030-inch coax, deduced frommeasurements numbers 7 and 8. 29

10 Computed calibration for the 0.030-inch coax. 30

11 Response of the MGL-7 sensor referenced to that ofthe MGL-8. 31

12 Response of the MGL-7 sensor with MGL-8 used asa standard. 33

13 Response of the MGL-7 sensor referenced to that ofthe MGL-8. 34

14 Response of the MGL-5 sensor with the MGL-8 usedas a standard. 36

15 Amplitude of the MGL-7 response compared with theSharpe-Roussi simulation. The dots show thefrequencies corresponding to the dominant polesin the 10-pole simulation. 38

16 Phase of the MGL-7 response compared with theSharpe-Roussi simulation. The dots show thefrequencies corresponding to the dominant polesin the 10-pole simulation. 39

iv

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Figure Page

17 Amplitude of the MGL-5 response compared with theSharpe-Roussi simulation. The dots show thefrequencies corresponding to the 18 poles used inthe simulation. 42

18 Phase of the MGL-5 response compared with theSharpe-Roussi simulation. The dots show thefrequencies corresponding to the 18 poles usedin the simulation. 43

19 Amplitude of a portion of the MGL-5 compared withthe Sharpe-Roussi simulation using 14 poles. 44

20 Phase of a portion of the MGL-5 compared with theShapre-Roussi simulation using 14 poles. 45

21 Sensors used in the study. 48

22 Modified MGL-9(R). (The coaxial cables were bent4.75 inches from the loop to adapt for H-verticalpolarization. In the original design the coaxwas straight.) 50

a 23 Twinaxial to dual-coaxial adapters. 53

24 Measurement geometry for the ACD sensors. (The•-variation produces the angular (dipole) response.) 55

25 Measurement geometry for MGL-series sensors. (Thea-variation produces angular (dipole) response and*-variation produces azimuthal (constant) response.) 57

26 Styrofoam jig used for support and rotation ofMGL-2 and MGL-6 sensors. (The incident field isfrom the right-hand side.) 58

27 Measured angular response of MGL-2D(A) at 150 MHz. 60

28 A (f) for ACD-4A(R). 62n

29 E2(f) for ACD-4A(R). 63

30 im (f) for ACD-4A(R), f61 < 600. 63

i 31 M(f) for ACD-4A(R), lel < 300. 64max

32 mx(f) for ACD-4A(R), e = 00. 64max

. . vi.

%V

1

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Figure Page

33 An(f) for MGL-2D(A), gap No. 1 at € = 90. 65n34 C2 (f) for MGL-2D(A), gap No. 1 at € = 900. 66

35 -M(f) for MGL-2D(A), lel < 600, gap No. 1 atmax 66=900.

36 6m(f) for MGL-2D(A), gap No. I at 0 = 900, lel < 300. 67max

37 6m(f) for MGL-2D(A), gap No. 1 at 0 = 900,max 67e = 00.

38 A (f) for MGL-2D(A), gap No. 1 at 0 = 45°. 68n39 E 2 (f) for MGL-2D(A), gap No. 1 at 450. 69

40 max (f) for MGL-2D(A), gap No. 1 at 450, lel <600. 69

41 6e (f), for MGL-2D(A), gap No. 1 at 450, !e < 300. 70max

42 6' (f), for MGL-2D(A), gap No. 1 at 450, e =00. 70

43 B n(f) for MGL-20(A). 71

44 '2(f) for MGL-2D(A). 72

45 r (f) for MGL-2D(A). 72max

46 A n(f) for MGL-6A(A), gap No. 1 at 0 = 900. 73

47 2(f) for MGL-6(A), gap No. 1 at o = 900, 7448 6m(f) for MGL-6(A), gap No. 1 at € = 900,

emax 74lel <600.

49 dma(f) for MGL-6A(A), gap No. 1 at 900, lel <_ 30 75max

50 (fmaxf) for MGL-6A(A), gap No. 1 at 900, e = 00.

51 A (f) for MGL-6A(A), gap No. 1 at = 450. 76n52 0 2(f) for MGL-6A(A), gap No. I at = 450. 77

53 ax(f) for MGL-6A(A), gap No. 1 at 0 = 45,

lel <60. 77

vi

• .I• " . . , . . o . . • . . . , . . : . .

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Figure Page

54 (f) for MGL-6A(A), gaps at = 450, jej 300. 78max55 ax(f) for MGL-6A(A), gaps at = 450, =00. 78

ma

56 B n(f) for MGL-6A(A). 79

57 e2(f) for MGL-6A(A). 80

58 6 r (f) for MGL-6A(A). 80I rmax

59 Response ratio of ACD-2/MGL-9. 83

60 Response ratio of ACD-4/ACD-2. 84

61 Response ratio of MGL-2/MGL-9. 85

62 Response ratio of MGL-6/MGL-9. 86

41

i

i.i

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TABLES

Table Pg

1 Components Studied 21

2 Measurement Combinations 22

3 Poles and Residues for MGL-7 40

4 Identification of Free-Space Sensors Used 47

5 Summnary of Results 88

Al List of ACD-4 Dipole Data Plots 91

BI List of MGL-2 Dipole Data Plots 107

Cl List of MGL-2 and MGL-6 Rotational Data Plots 136

viii

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1. INTRODUCTION

An electromagnetic field sensor is a special purpose receiving

antenna which converts a given electromagnetic field quantity into a

voltage or current according to a prescribed relation. The relation

should be as simple as possible, e.g., a constant of proportionality,

or a linear form involving frequency or time.

As is true with most instruments, however, there is a maximum

frequency (frequency domain) or minimum rise time (time domain) beyond

which the simple relation no longer holds. In general, the smaller

the sensor, the larger the frequency range over which the performance

can be prescribed. Since the output of a time derivative sensor is

inversely proportional to its size and directly proportional to the

frequency, the output of a particular sensor may not be large enough

for accurate measurements at low frequencies. In this case one could

choose to use a larger sensor to obtain a bigger output at the expense

of reducing the upper frequency limit for the prescribed behavior. If

used at frequencies beyond this limit (the roll-off frequency),

erroneous data will result; and though two sensors of different sizes

might seem to constitute a solution, their use would complicate the

data acquisition procedures. In addition, there may not be room on

the test object to mount more than one sensor.

For these and other reasons, it is desirable to obtain as much

information as possible about the behavior of the sensors

,4

.- ,

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that are used. The purpose of the present study was to investigate

and analyze the responses of various EMP sensors over a frequency

range extending well beyond the so-called 3-dB roll-off frequencies.

The sensors which were studied were the MGL-2D(A), MGL-6A(A) and

ACD-4A(R) free-space sensors, and the MGL-5B(R) and MGL-7A(R)

ground plane versions. In each instance the responses were measured

as a function of frequency and, in addition, for the free-space

sensors, the dipole patterns and rotational symmetry were determined.

The mathematical formulas which define the responses and which

were used in analyzing the data are presented in Chapter 2, and this

.- is followed (Chapter 3) by a description of the experimental facility

* . used to make the measurements. Chapter 4 is concerned with the

ground plane sensors and includes a detailed presentation of the

data and the results of the analyses. The majority of the effort

was devoted to the free-space sensors, which are treated in Chapter 5.

The significant results are summarized in Chapter 6 in a manner such

that the performance of the various sensors can be compared.

-2-

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2. GENERAL FORMULAS

"g Since the MGL and ACD electromagnetic field sensors were developed

to measure electromagnetic fields in the time domain, it is natural to

evaluate them in the time domain by measuring their impulse or step

responses. In general, however, such tests are not accurate enough to

quantify their detailed performance in the frequency domain. This is

particularly true at the higher frequencies where the response cannot

be deduced from the time domain behavior because of instrument and/or

recording limitations, and in the study reported here the frequency

response of the MGL and ACD sensors was measured directly in the

frequency domain,

2.1 Theoretical Considerations

The sensors that were tested were designed [1] to provide a simple

mathematical relation between a designated field quantity and the output

voltage over a wide range of frequencies. For the ACD sensors the

voltage response is [2]

V0(t) =R0 A - E(t) (time domain)

(1)or

Vo(f) = j27fco A E(f) (frequency domain)

-3-

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where V0 is the sensor output (volts),

::'-iR is the sensor's characteristic load impedance

(usually 100 ohms),

A is the sensor's equivalent area (inm2 ),eq

(367r) " 10"9 (Farad/m),

E is the electric field intensity (volt/m),

f is the frequency (Hz),

and a time dependence exp(j27Tft) has been assumed. For the MGL

sensors,

V eq dH(t) (time domain)

or (2)

V 0 (f) = j2rfuoAeq H(f) (frequency domain)

where io = 47 x l0 (Henry/m) and

H is the magnetic field intensity (Ampere/m).

Each sensor is a calibrated device, and its equivalent area is

specified.

The above formulas can be obtained by retaining only the dipole

terms in the low frequency expansions of the responses, and are valid

for sufficiently low frequencies. As the frequency is increased, the

influence of higher order multipoles becomes significant, leading to

" -i a response which is no longer linear in frequency and does not have

the aspect dependence characteristic of a dipole, e.g., the dot

product (cosine) behavior as a function of angle.

-4-

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The coordinate systems used in analyzing the measured data

for the responses of the ACD (electric dipole) and MGL (magnetic

dipole) free space sensors are shown in Fig. 1. In each case the z

axis is fixed by the sensor, and the relevant incident field vector

(E for the ACD sensor and H for the MGL sensor) is chosen to be in

the 0' direction of a spherical polar coordinate system (r,e',f). The

frequency domain responses (1) and (2) then become

V(f) = j27f Re A E(f) sin e' (ACD) (3)0 o eq

Vo(f) = j2rfmo AeqH(f) sin e' (MGL) (4)

and both can be written as

V(e',O;f) = A(f) F sin e' (5)

where A(f) is a function of the frequency alone and F denotes the

appropriate incident field quantity (E for the ACD sensor and H for

the MGL). Outside the frequency range where (1) and (2) are

applicable,

V(e',;f) = {A(f) sin e' + c(e',4;f)} F (6)

where e is an error term embodying, amongst other things, the effect

of the higher order multipoles.

-5-

° -

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. - -A .01

z 0..

(b Manei loo eel'L

Fiue . Coriat yse se orteoeialaalss

-6

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To determine A and e from V, the standard procedure is to

expand V(e',O;f) in zonal harmonics [3], so that

V(e',O;f) = A(f)Pl(cos ') + {terms in e',o,f}1

where V is the recorded signal normalized relative to the incident

field strength, i.e., V = V/F. We can now find A(f) by using the

orthogonality properties of the zonal harmonics. If V is assumed

independent of 0, multiplication by Pl(cos e') and integration over

4Tr steradians (do = sin e' do' do) gives

A(f) 3 V(e',O;f) sin 2 e' do' (7)

0

We note in passing that if the entire right-hand side of (6) is assumed

to be independent of 0 rather than just the first term, an alternative

approach is to expand V in a Fourier sine series. This leads to an

alternative weighting factor in (7) which gives more weight to the

angles at which the sensor is end-on, but is less defensible as a

general procedure.

From (7) the mean squared angular error is defined as

=fIv(e',O;f) - A(f)sin 0'12 do

f IA(f) sin 6'12 dQ

-7-

-I

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i.e.,

'-. [A(f) 2 V'f

s2: 2(f) :) I fV(e',o;f) - A(f)sin e'12 sin 6' de'4..,

0 "(8)

and is a measure of the mean squared deviation of the angular response

data from the dipole behavior. The maximum error ax (f) is-. "max

likewise defined as

"maxV(e',f) A(f)sin o'""- . .'ma(f) maxi" = max

IA(f)sin e'

.max < e 'eax (9)

and indicates the maximum deviation from the dipole pattern over a

*m specified angular range.

2.2 Practical Considerations

In antenna work the angle defining the angular response or

pattern is generally measured from the direction of the peak response,

and this is the convention used in the sensor catalog [2] where,

-for example, data sheet 1118 cites the response of an ACD sensor

as

V - RA d or V - RA d Dcos e. (10)eq dt eq dt

Here, e is the angle between the direction of the vector equivalent

area Aeq and that of the appropriate field vector, so that

-8-

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e - /2(11)

where e' is the spherical polar angle defined in the previous

section. For consistency with the literature, we shall henceforth

express all results in terms of e, where -r/2 < 8 < 7r/2.

Consider also the nature of the signal v(e,0;f) present at

the output of a sensor. In practice,

v(e,O;f) = V(e,o;f) F K (12)

where V is the sensor response to a unit incident field, F is an

incident field of unknown strength, and K is the response of the

chamber, cables, amplifiers, etc. In our measurements it is

postulated that F and K are time invariant, and thus, for example,

the ratio of measurements made for some value of e and for 8 = 0

(broadside) at two different times yields

Vn(O,¢;f) = V(o,;f) (13)n V(0,0;f)

where V is independent of F and K. V n(e,;f) is the response".- n

relative to that of the same sensor at broadside incidence, and

(7) through (9) are readily expressed in terms of this normalized

quantity:

-9.

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*.. .. . .. - ° - : : -/ " I . . . . .

A3 Vn(O;f)cos2 e de (14)

7r/2

4(f) -f ( ;f) A(f)COS

-7/ (15)

IV (e,;f) - A (f)cos 91emax(f) = max , o < ( e m (16)

m IAn(f) cos el

In the derivation of (7) through (16) it was assumed that

the sensor response is independent of (see Fig. 1), and 0 has been

shown as one of the variables of Vn only for generality. For the

ACD sensors the response is € independent from symmetry, but this

is not true for an MGL sensor. The free-space version evaluated

in this study has four gaps which, at low frequencies, should be

"invisible." As shown later, however, at high frequencies the

response is affected by the orientation of the field with respect to

the gaps.

To assess the rotational response of the MGL sensors, an

average rotational response coefficient is defined as

n(f) = F Vn(O,0;f)d (17)

0

(cf. (14)). By analogy with (15), the mean squared rotational error

is

o"

-.. ~ - 10- . " . . ' . -

Page 24: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

27r= B (f-2fJ(O;)-B (f)12 do 182w(f n~f I1 n fl~) (8

0

and the maximum rotational error is

IV n(0,0;f) B B(f)j6' (f) =max (19)

r maxIBn(f)I

The formulas in (14) through (19) were progranmmed in BASIC

for the HP9845 calculator, and results are presented in Chapter 5.

Page 25: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

3. EXPERIMENTAL FACILITY

The measurements were made in the University of Michigan's

surface (and near) field facility, a block diagram of which is

shown in Fig. 2. The system is a CW one in which the frequency is

swept (stepped) over a wide range, and a key part of the facility is

a tapered.anechoic chamber approximately 50 feet in length. The

rectangular test region is 18 feet wide and 12 feet high. The

rear wall is covered with 72-inch-high performance pyramidal absorber,

with 18-inch material used on the side walls, floor and ceiling.

The material in the tapered section (or throat) is 2-inch hairflex

absorber. The chamber can be thought of as a lossy wall horn antenna

terminated by the rear wall. The signal is launched from a single

exponentially tapered broadband antenna located at the apex of the

chamber. The antenna is fixed and since the radiated signal is

horizontally polarized, the pseudo plane wave in the center ('quiet

zone') portion of the test region is also horizontally polarized.

The instrumentation is centered around a Hewlett-Packard

8410B network analyzer, and is computer controlled. An HP9830A

calculator controls the frequency to be generated, switches in the

appropriate power amplifiers and low-pass filters, and reads and

stores the amplitude and phase of the signal picked up by the

sensor. During a run, the frequencies are typically stepped from

118 to 4400 MHz. Because of the limited memory size of the

calculator, this frequency range is recorded in four bands: 118 to

550 MHz (in 4.8 MHz steps), 550 to 1100 MHz (in 4.8 MHz steps),

-12-

Page 26: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

CC,--

Al C. l

III

-0--

Cl 0L

Cc r- -

~~.0~~C -.----- -

CC m

i I

Page 27: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

1100 to 2000 MHz (in 9.6 MHz steps), and 2000 to 4400 MHz (in 16 MHz

steps). The data from each band are stored by the HP9830A calculator

- on a cassette for later transfer to an HP9845B calculator which

processes and plots the data. If substantial processing or

computation is involved, or if a need exists to write the data on

standard computer tape, the data are transmitted to the central

University of Michigan AMDAHL/V8 (IBM compatible) computer.

The signal picked up by the sensor is a function of the

response not only of the sensor but also of the entire facility,

including chamber, antenna, amplifiers and cabling, and it would be

a virtually impossible task to separate out the contributions of each.

An alternative approach is to apply some form of calibration or

normalization whereby the facility response is, in principle,

eliminated. When measuring the surface fields on, say, a scale model

aircraft, two distinct measurements are made using the same probe

or sensor: one on the aircraft, and the other on a metallic sphere

or other object whose surface field is known. In conjunction with the

known sphere solution, the ratio of the two measurements gives the

aircraft response relative to the incident field.

In the present study, two different calibration procedures were

used. To determine the angular response characteristics of a sensor, the

data were normalized to the measured values of the maximum response

.0 (broadside incidence) for the same sensor. This eliminated the effects

of any cable mismatch. To obtain the frequency response, each set of

measurements was followed immediately by the analogous measurements

-14-

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for a small sensor such as the ACD-2(R) or MGL-9(R), whose response

is believed uniform and predictable out to frequencies beyond

those of interest for the original sensor. The procedure worked wellfor the ground plane sensors (Chapter 4), but the results were less

satisfactory for the free-space sensors (Chapter 5). One reason

for this was the presence of currents induced on the sensor leads

by "stray" fields in the chamber that ultimately affect (especially

the ACD-type) sensor response, but a more severe problem was caused

by the mismatches in the twin-axial leads, particularly at the twin-

coax to twin-axial junctions.

- The details of the measurement procedures for each type of

sensor are described in the section devoted to that sensor.

-.1

1'-15-

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- - -

4. GROUND PLANE SENSOR EVALUATION

Although the study was primarily directed at the MGL and ACDN! lines of free space sensors, it was felt prudent to start with MGL ground

plane sensors to gain experience in the simpler situation that results.

Because of the ground plane, the possibility of any lead interaction is

greatly reduced, and, in addition, the probes do not have the aspect

sensitivity that the free-space ones do.

,* In the following sections we describe the ground plane that was

used, the measurements that were carried out on three different MGL

sensors, the calibration of the various components involved, the deduced

frequency responses of two of the sensors referenced to the response of

the third, and the implications of the results obtained.

4.1 Ground Plane

Ideally the ground plane should be infinite in extent, and one

consequence of using a finite size is that the surface field departs from

its infinite plane value due mainly to the effect of the edge currents.

For normal incidence on a plane several wavelengths in dimension, the

departures are primarily due to the edges perpendicular to the incident

electric vector that set up a standing wave pattern across the plate.

The influence of the other edges is confined to a distance of a wavelength

(or less) from them.

For use on another project it was necessary to design and

fabricate a ground plane which was small enough to fit comfortably

-16-

I."

Page 30: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

inside the anechoic chamber but which still simulated an infinite plane

over at least a central portion of the surface. To reduce the surface

" field perturbation created by the vertical edges, resistive sheets were

added as shown in Fig. 3. Each sheet was shaped like a quarter

cylinder of radius 25.5 in. and had a resistivity which increased

quadratically as a function of the surface distance from the metallic

*plane. The effect of different resistivity variations was determined

by numerical experiments carried out using codes based on resistive

strip formulations, and the resistivity that was finally selected started

with zero at the edge, increasing quadratically to about 1000 ohms/square

at the rear.

The sheets were fabricated by spraying thin layers of resistive

material on art paper. After each treatment the resistivity was

measured with an ohm meter, and the process repeated until the appropriate

resistivity profile was achieved. The final products had a resistivity

which started at about 10 ohms/square and increased to the required

value of 1000 ohms/square at the outer edges. Although the surface

fields on the metallic part of the resulting ground plane have not been

measured, it is inferred from the numerical experiments that over a

central portion of the plane at least, the fields are virtually

identical to those on an infinite plane.

4.2 Measurements and Calibrations

The MGL line are B-dot sensors with specified equivalent area Aeq

Three different size versions were available for this study:

MGL-5B(R), serial no. 14, having Aeq = l m" i 2 ; MGL-7A(R), serial no. 5,

eqq-. having Ae 10-4 m2; and MGL-8A(R), serial no. 1, having Ae 10-5 m2

-17-aI

.........

Page 31: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

40 inch sheets

52 in.

B -dotsensor

j 48 in.

-. 1000 Q/sq ___________

0~0 2/sq.

48 in.

Figure 3. Resistively loaded ground plane used in the measurements.

-18-

Page 32: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

• •• . . .V. - o • , ' • , . .

All were manufactured by EG&G Inc. and are described in their

catalog [2]. Figure 4 is a photograph of the three sensors.

Each sensor was mounted in turn at the center of the ground

plane in our surface field facility, and its output was measured as

the frequency was scanned (or digitally stepped) from 118 to 4400 MHz.

To connect a sensor to the system it was necessary to use adaptors

as indicated in the first three lines of Table 1. These adaptors are

henceforth regarded as part of the sensors, and no attempt has been

made to compensate for their presence.

Any quantitative measurement is, by its nature, a comparison

process in which the reference is either the response of the same

system to a known field, or of a calibrated system to the existing

(unknown) field. For the sensor measurements the incident field was

unknown, but reproducible over a sufficient length of time to enable

each sensor to be mounted in turn at the same location on the ground

plane and have its response to the same field recorded. Any one sensor

can therefore serve as the reference for the other two.

In practice, however, there is a difficulty. To connect a sensor

to the measurement lead requires a length of coaxial cable, and because

of the larger outputs from the larger sensors, attenuators must also

be inserted. To eliminate their effect, it is necessary to calibrate

both the cable and the attenuator. To do so, two cables and two

attenuators were used as indicated in Table 1, and measurements were

made on various combinations of these sensors, and the four components.

The measurements performed are listed in Table 2.

-19-

Page 33: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

Figue 4 Phtogaphof the ground plane sensorsusdi th

r'iure'~ evaluation.un

-20-

Page 34: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

TABLE 1. COMPONENTS STUDIED

Component Description

MGL-8A(R) B-dot sensor, Aeq = 10- m2, Ser. No. 1; with BRRM(F) *

OSSM(F), OSSM(M) - OSM(F) adaptors

,4 2

MGL-7A(R) B-dot sensor, A = lO- m2, Ser. No. 5; no adaptorseq.

MGL-5B(R) B-dot sensor, A = lO" m2, Ser. No. 14;h eq.

GR SMA(F) adaptors

20-dB attenuator Attenuator, Midwest Microwave, Model 444-20

6-dB attenuator Attenuator, Midwest Microwave, Model 444-6

0.020-inch coax 35.5 cm long coax with OSSM connectors at each end;

Uniform Tubes, UT20

0.034-inch coax 61.6 cm long coax with OSSM connectors at each end;

Uniform Tubes, UT34

-

.D."L I-21 -

6j

Page 35: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

La.. LL..0

cmI 0 0 4-jLL. Q. Q E

-L CD LA- a

Ln to' IU LL. I LL. ia - a

0 4DCD I~ 09

0

4-))

% L) L)

to

4) CD CD a11 %EU j r. 1 . . %r4 %

0. CD CD0 CD CD CD. CD CD

EUUC..) EUj

Q- VU4)

to U0

LAJ0 0 0 0 0 0 0 0 0C

04m

0D 0D %0 w C 04w0 L

C*.J 0

CD (z C D D C CD CD CD C

4A W

4-)

4) 61 V)L

ILp 77 77 77rr r. . l *41 CL C CL CL U u

too4) 4)

C e -t Lc, w r, cc) r-. c-L

EU ~ ~ ~ -22-

Page 36: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

From measurements numbers 5 and 7 using the MGL-7 sensor with

and without the 20-dB attenuator, the effect of the attenuator can be

found. The ratio of the measured outputs is the response of the

K attenuator, and its amplitude and phase are plotted in Fig. 5. Although

the amplitude is slightly noisy, the noise is almost certainly due to

mismatches in the system rather than to the attenuator itself. Indeed

the attenuator is a physically small device with a specified operating

range of 0 to 18 GHz, and should have a constant response up to and beyond

the highest frequency used in the measurements. This would seem to

justify taking an average value for both the amplitude and phases. From

Fig. 3 the average amplitude is 0.1019 (= -19.48 dB), and the average

phase is -0.0326667 degrees/MHz. The latter is equivalent to an effective

free space length of 2.722 cm.

Similarly, from measurements numbers 6 and 7 the response of the

6-dB attenuator can be found. The amplitude and phase are shown in

Fig. 6, and average 0.5183 (= -5.71 dB) and 2.387 cm of electrical

length, respectively.

The same procedure was also used to calibrate the coaxial cables

(see Table 2 for the data sets involved), and the results for the

0.020-inch coax are shown in Fig. 7. The noise is again attributed to

the entire system rather than to this single component, and since the

skin effect is the main source of cable loss in this frequency range,

the amplitude of the response should be exp(-ct/f) where a depends on the

length and characteristics of the cable, but is independent of the

7. frequency f. By eyeball fit, the (average) amplitude at 3000 MHz is

estimated to be 0.8, implying a = 7.438 x lO" per MHz. The resulting

-23-

- -

Page 37: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

* --

" '%CRL r :jP 2 -0 1 R TT , .,

r 157 t lH

- I4". - -.

uIHI

k -U

1 U--C ..-... ... . ---

* e Il{.l_ iYL..C' Cn' i O4] C'C3C..,....

Figure 5. Calibration of the 20-dB attenuator, deduced from measurementsnumbers 5 and 7.

-24-

Page 38: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

%-J

-. .'--

.-7L 0,. I. C .

.- 25

ILI

• i

I0 -- I - . .~.~

u ij-

i ''

21 Figure 6. Calibration of the 6-dB attenuator, deduced from measurements

.. numbers 6 and 7.

,'-' -25-

Page 39: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

"" ,,A-:L P3 . 2 0 :.: 4 41

1.5

z U-

U11

-26

-I I *.

1. . ? ..1 I i . ....... ... .. ...

Ii I ,,u~ ;. IIH-

iinI

i, lilI 1 I.

I I

' I II \ l

" '.

Figure 7. Calibration for the 0.020-inch coax, deduced from measurementsnumbers 9 and 10.

.. -26-

ad

Page 40: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

amplitude curve is shown in Fig. 8 and is seen to provide a good

fit to the measured data. The slope of the phase curve is likewise

-0.61463 degrees/MHz, corresponding to an effective free space length

of 51.216 cm, and the computed phase curve is given in Fig. 8.

The analogous results for the 0.034-in. coax are shown in Figs. 9

and 10. With the amplitude chosen to be 0.808 at 3000 MHz, the deduced

is 7.106 x l0" per MHz, and the slope of the phase curve is -1.0556

degrees/MHz, corresponding to an effective free-space length of 87.970 cm.

4.3 Sensor Responses

Measurements numbered 3 and 4 (see Table 2) were done with the

MGL-7 and MGL-8 sensors respectively, using the same cable and attenuator,

and the ratios of the measured data are shown in Fig. 11. At low

frequencies the ratio is 9.33, compared with the value 10 obtained from

the equivalent areas. The discrepancy is believed due to the small size

of the MGL-8 sensor whose construction is inevitably difficult. The phase

is zero at low frequencies, but deviates at higher frequencies, due not

only to the effect of the sensors individually, but also to the inclusion

of the adaptors whose presence has not been compensated for.

The MGL-8 is the smallest sensor of the three, and its response

should be linear out to (and beyond) the highest frequency used.

According to the quasi-static approximation, its output voltage should

therefore be

dV wIIHA eq

where w is the radian frequency, p is the permeability of free space

"( 1.2566 x 0"6), H is the amplitude of the magnetic field, and

-27-

Page 41: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

-Jk::

'~~I . .. . . .. ... . .. . .. . . . .... .

I ti

"I

kI'

I'

11,0 f1

Q I

I I

-28--

-'lF g r 8 . Co p t d c l b i on f r t e O 0 0 i o xI Io.

Page 42: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

I .L b;..c W..; %

Li

C-29

r., ...

%I ,

F Fr

"S.a"- V .. .. .. .. . . . ..... . . . .. .

, i ' ' L V 'U r I , i-4z

Fiue9 arto o h 034ic c, deue from measuement* number 7 and 8

I-29

C'

il" 1 ! n , l ]2

Page 43: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

low. -0

-rJ

13 I ( 4

LI C '-!H

I Figure 10. Computed calibration for the 0.034-inch coax.

-30-

Page 44: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

- -___-- __ _ -

-. ,31

I cI:- .- -- -- . ....-- . _.... -.. . --

0 !@ O~ L00 ":c1 40%8 - :,:

* ,

C-4LI

310

I

0 I0 00 2000 i0 4 0L0 .

F'..Ey 'C r arIHz,

Figure 11. Response of the MGL-7 sensor referenced to that of the MGL-8.

-31-S

Page 45: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

5 2

Aeq I0-s m2 On multiplying the data in Fig. 11, by jwuA , we

obtain the response of the MGL-7. The behavior is not unexpected, but

the droop in the amplitude curve at frequencies above 4000 MHz was not

present in some of the earlier data, and may be due to an equipment

mal functi on.

The ratio of the measured responses of the MGL-5 and MGL-8

sensors is shown in Fig. 13. At low frequencies the ratio is 90.0,

compared with the value 100 predicted by the equivalent areas of the

two sensors. At a frequency of about 500 MHz, there is a sharp notch

in the curves, the origin of which is not clear at this time. It

" . occurs in all data that have been obtained with the MGL-5 sensor, and

is therefore associated with this sensor rather than the MGL-8.

In an attempt to locate its source, the measurements were

repeated with the front of the sensor retaped to the ground plane. We

also taped the back of the sensor assembly where it protrudes through

the ground plane to eliminate any possibility of resonances in a cavity

formed by the plane and the plate on which the sensor is mounted. There

was no change in the data, and it would therefore appear that the

- -notch is a feature of this particular MGL-5 sensor.

To test this, it was susggested [4] that the sensor be examined

electrically using a time domain reflectometer, and visually as well.

It was found that the two 100-ohm lines from the gaps have an

electrical length of about 15 cm, but one is about 1 cm shorter than

the other. Because of the design of the sensor, the two lines and the

-32-

Page 46: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

F~ ~ ~~1: HI.-~gr~;F-z

I Oct

I. -"F .': r"

/ r

--- 3

Fiue 2 esoseooheML-o eso ih h ,L8usdasasanad

r-33

Page 47: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

I0 Ot -------------- -___ ____________

M-L- :L -

4 0

-J 40

'IC-10.. -:0 1c:

Figur 13C r -7 70 1000-0 . .. C

Figur 13.Response of the MGL-5 sensor referenced to that of the MGL-8.

7 .-34-.

Page 48: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

loop can form a high Q resonant circuit for excitation in the

anti-symmetrical mode, and if the 100-ohm lines are not of equal

length, the resulting signal could create the notch at 500 MHz.

In presenting the responses of the MGL-5 and MGL-7 sensors, the

MGL-8 has been used as a reference because of the expected linearity of

its output over a frequency range exceeding the highest frequency used

in the measurements. On the other hand, its small size increases the

probability that its specified equivalent area is less accurate than

those of the larger sensors. To judge from the low frequency limits

in Figs. 11 and 13 it would appear that the actual value of Aeq for the

MGL-8 exceeds lO m2, and a more probable value is (say) 1/2{(0.933) "'

+ (0.966)'1}0 " m 2, i.e., Aeq = 1.054 x l0" m2. The resulting

recalibration of the MGL-5 and MGL-7 responses would uniformly increase

the amplitudes in Figs. 12 and 14 by 1.054.

4.4 Discussion

The amplitude and phase of the frequency response of the MGL-7

sensor are shown in Fig. 12. At low frequencies, the response increases

linearly with f according to the formula

e q ' (20)

with A = 0.933 x 10-4 M2 . It rises above the value predicted by (20)

eq

starting at f = 800 MHz, indicative of the growing influence of the

multiple contributions, and then recrosses the linear curve at about

1800 MHz, where the response has its (initial) peak value. Thereafter,

4 the amplitude falls increasingly below the linear curve, and is more

than 3 dB below for all f > 2300 MHz.

-35-

6

Page 49: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

o1r-1& riGL- :R Z

II

-IS

Figure 14.=_ Repos of, thG eso ihteM L- use as. a... adard

-J j ,- /

,I-- . A /II - -,".

. . v,-*.,j ". 7 - -

Rt'-£ -LIE-IC

V I

•1 , [, /'I":J I

, /

a . ' ---

- INy. .- - - l-4 l'J- rl- I ,

S J~'- Cxu zCO~-4lLLb

* F't :i ! M z

.iue1. Repne fte G- sesrwtIh G- sda tnad

u-36-

6,

Page 50: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

Some additional information can be obtained by applying the

Sharpe-Roussi program [5] to give a partial fraction representation of

a real (as a function of s = jw) rational function approximation to the

ro response. For this purpose it is convenient to write the response as a

function of w in units of l09 radians/sec. Using ten poles, the fit

to the measured amplitude and phase is shown in Figs. 15 and 16, and

we note that even the small amplitude dip near 4000 MHz (w = 25) was

faithfully reproduced. The poles and residues are given in Table 3.

The resonant frequencies are therefore 12.19, 18.10, 25.58 and 26.23

G rad/sec, but because of its small residue, the one at 25.58 can be

ignored. The other three are indicated in Fig. 15. The fundamental

corresponds to that of a loop of radius 2.496 cm, and the next two

values are then consistent with the first anti-resonance and the second

resonance, respectively. It is not known whether the loop radius can

be identified as the dimension of a specific structural element of

the sensor.

For w << 12, the partial fraction representation of V can be

expanded as a power series in w, giving

V = -0.0216 + jw 0.1174 + w2 0.001678 + jW3 0.0001399 + 0(W4)

(21)

The non-zero constant is physically unrealistic, and is due to noise

in the measured data and/or the approximations inherent in the

numerical simulation. The dipole contribution (proportional to jw)

implies (see eq. 1) A' = 0.934 x 10 i 2 in excellent agreement witheq

-37-

• .U. _ . . " . - ', _ . . . . . .. • . . , . . . . - .

Page 51: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

0 C

CD

CL

4-)

*- 0_

A 4-C.Q00

CL- 4

(A-

0 CA

-J 0.4-J

a 0) 0

CY 4-0

* *L0.

r. 3-

Page 52: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

0 0a

-J

CIL

CD~

'0041 C

)0.

Im

Es- * . 0

-39-

Page 53: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

TABLE 3. POLES AND RESIDUES FOR MGL-7

Poles wi Residues R.

12.19 + j4.452 1.521 - j2.839

-12.19 + j4. 452 -1.521 - j2.839

18.10 + jO.9277 0.1528 -jO.008782

-18.10 + j0.9277 -0.1528 -jO.008782

25.58 + jO.4500 -0.01499 + jO.07588

-25.58 + jO.4500 0.01499 + jO.07588

26.23 + j2.384 -2.703 - l.759

-26.23 + j2.394 2.703 - jl.759

j83.96 j277.7

j93.29 j311.5

-40-

Page 54: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

the value deduced from Fig. 11. The other terms in (21) are then the

next higher order multipole contributions, and bearing in mind that

- (21) requires w << 12, their coefficients are remarkably small. Although

S-these terms are responsible for the initial departure from the linear

behavior with frequency, it is evident that a study of the quadrupole

contributions to the sensor response would provide little in the way

of an improved representation of the output.

For the MGL-5 sensor the amplitude and phase of the response

(see Fig. 14), replotted as a function of w in G rad/sec, are shown

in Figs. 17 and 18, along with the simulation provided by the Sharpe-

Roussi program using 18 poles. The frequencies appropriate to the pole

locations are indicated, and we observe that these do not always

correspond to the peaks and nulls in the response. Nevertheless, the

overall fit is excellent except at frequencies in the vicinity of

= 3.7 where the notch occurs, and where the simulation averages

through the increased response at the lower frequencies and the

subsequent deep null. Because of this, the low frequency behavior

of the simulated voltage differs from the known behavior of the sensor.

Indeed, by expansion of the partial fractions we obtain

V = 0.0607 + jw 1.135 + O(W2)

= 0.903 -3 2implying A'q 0.903 x 10 m which is still seven percent less than

the value obtained from Fig. 13.

By applying the Sharpe-Roussi program to the low frequency

portion of the curve up to w = 10, the notch at w = 3.6 is faithfully

V reproduced using 14 poles, as shown in Figs. 19 and 20.

-41-

L. . ---. _.

Page 55: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

-J

c

s-

01.

•E 0

o -

I -

- * IE

S).-

4-

(4- c

CL W

U.- -V

, o 4

4Cfl

o -4 2 -

I

• 4o(..)

• -42-

Page 56: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

-&n 4

U7)

4.)

:4 4I-.-

C3,

0

q) 4-)

I It)

z (A

3SV~d-~C 4.WK *v-c-

cm0

-43-~

Page 57: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

"W~~-~ .... .... .... .... .WWI

41

Loo

I-!-

tic

x 0L

LC

Zi,

U-

-44-)

Page 58: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

lop)

00

CC

*1u

it-j

*n 0.

L

-(40'

0 00

IL.)

-45

Page 59: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

5. FREE-SPACE SENSOR EVALUATION

Apart from its intrinsic value, the preceding study of ground

plane sensors was helpful in enabling us to develop the experimental

techniques necessary to tackle the more difficult problem of

evaluating the free-space sensors.

5.1 The Sensors

The free-space sensors studied were the MGL-2D(A), MGL-6A(A)

and ACD-4A(R), but in addition the smaller size MGL-9(R) and ACD-2(R)

were used as references for the frequency variation study since their

regions of linearity extend well beyond the largest frequency used

in the measurements.

. Table 4 identifies the particular sensors, and we note that

"- two MGL-6's are listed. Because of the poor performance of the

first model (serial No. 2), it was felt that the sensor was defective,

K; and a second model (serial No. 1) was requested from the Air Force.

It turned out that this was no better, and we eventually decided to

employ the second one only. Figure 21 is a photograph of the five

sensors used in the study, with the ACD-4 and ACD-2 on top and the

.* MGL-2, MGL-6 and MGL-9 below. The dual coax leads on the MGL-9

have been bent through 90 degrees to make the sensor compatible with

the other two. Since the incident electric field in the chamber is

horizontai, it was necessary for us to bend the original straight

leads to enable the sensor to receive the (vertical) magnetic field

-46-

Page 60: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

4- E

r_ 0-.O4-1-4--

U((A

C 4-)CJ .(A u

U= 4-) 04- .0 C~

0 to-( a - . 0 U(x -0 W (U1

tz 0 4 V) toaJ4-- ~ ~ ~ . 3_.1 ... , )

(1 4- Aa

aI. 44)* c(UU sJ0J 0

u4- 4-) Ln4nfl go O c cu

C -)n X -L = -u

Li.)

LO Iui

A1

0)0e

- 0 01-J 0 . -I

- (ULi.) r-.LJ C) CDW C)LJ 1

4- 1oa e DO. r- *a -~ a CS aLL. ~ ~ ~ ~ I s-C C )CD mC M0tio ~ ~ r- r-= R* L-. .J ( U

LLUG

OC E~ CD a-C ODC>~~~~ Ua OQDCDaCco C 0 CD

I- - * * LO .0 *M * *X, CDr-% O CD Mc Or- Or- Or

0 ui

4JI

V~ 0 x x -CL aj 41 4 tZ .) o 4 to 4to 4

ea I 3c 1 3L) co CL CO L36

-47-

Page 61: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

ACD-4A(R) ACD-2(R)

MGL-2D(A) MGL 60(A) MGL-9(R)

Figure 21. Sensors used in the study.

-48-

Page 62: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

with the leads vertical. Figure 22 is a close-up of the region near

the bend. The coaxial cables were unsoldered and separated up to

about 4 inches from the loop, bent with a radius of about 3/4 inches,

and then resoldered to avoid the possibility of any loop resonances

on the leads.

5.2 Experimental Techniques

The chamber and its instrumentation were described in

Chapter 3 and, in principle at least, measuring the frequency response

of the free space sensors is straightforward. Each sensor is

positioned and supported inside the chamber arid itfi output recorded

over the frequency range from 118 to 4400 MHz. The sensor is then

replaced by the smaller sized calibration sensor (MGL-9 or ACD-2)

and the measurement repeated. From a knowledge of the latter's

response, the ratio of the two outputs gives the normalized response

of the original sensor.

This procedure worked well for the ground plane sensors. The

same signal lead could be connected directly to the base of each

sensor and, in addition, all the cabling was beneath the ground plane

where it was invisible to the incident field. The situation is very

different with the free space sensors. For example, each of the

MGL-2, MGL-6 and ACD-4 sensors has a pair of coaxial cables extending

out about 18 inches from the sensor and terminating in a connector.

The connector is a so-called twinaxial where the transition is made

from the pair of coaxial cables to a twinaxial cable. At the far end

.of the twinax, a transition is again necessary to go to the 50-ohm

-49-

0

Page 63: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

Pair SMIA (jack) connectors

Pair 0.085 in. dian.semiricid coax

H

4.75"

KFigure 22. Modified MGL-9(R). The coaxial cables werebent 4.75 inches from the loop to adapt forH-vertical polarization. In the originaldesign the coax was straight.

-50-

Page 64: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

, k . '. . . - .- . L- -

- -, . _ . ii'

. ." - ." " . . .. . . . - . - . .. .-

coaxial geometry required by the network analyzer. Although

balanced to unbalanced transformers are available to fit the

connector (EG&G, DLT-96 series), they are usable up to 130 MHz only,

and therefore inappropriate to the frequency range of concern to us.

An alternative is to change from the twinaxial transmission line

geometry to a twin coaxial one, and to record each of the two outputs

individually, combining them digitally using the calculator. A device

called a twinaxial connector (EG&G, TCT) is available, but

unfortunately it is quite bulky. To avoid interference with the field

inside the chamber, it is necessary to place it outside, which then

requires a long length of twinaxial cable from the sensor. Because

of the discontinuities produced at the two connectors, standing waves

are set up on the twinaxial cable which show up as oscillations

in the measured data. Though we tried to reduce the oscillations using

a 6-dB twin-line attenuator which we designed and built for insertion

in the twinax, the resulting data were still unacceptable.

We remark in passing that the removal of the twinaxial connector

at the sensor would give direct access to each of the coaxial leads

from the sensor, and eliminate most of our problems. However, this

would modify the sensor, and since our results would not then be

appropriate to the sensors as built, this simple solution was

unacceptable.

By this time we had concluded that the most practical approach

was to separate the twinax into two coaxes as close to the sensor as

possible, thereby minimizing oscillations due to cable mismatches.

4

-51-

I.

Page 65: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

A miniature twinaxial to coaxial adaptor was constructed using

twinaxial and General Radio coaxial connector parts, and this is

shown in Fig. 23 along with the TCT-lA connector. The adaptor is

no larger than the twinaxial connector and has two 0.141-inch-diam.

semi-rigid coaxial cables with SMA connectors coming out. Because

of its small size, the adaptor can be attached directly to the

sensor and the signal can then be taken out of the chamber dith a

pair of semi-rigid cables; and since these cables and the connectors

have low VSWR, they produce no appreciable mismatches to affect the

data. The mismatches that remain are at the sensor, twinaxial

connector and the adaptor. These are all close together, and the

oscillations that they produce in the frequency data are relatively

slow. Such oscillations are of no concern if a sensor response is

calibrated against the response of the same sensor at a different

aspect, provided the associated cabling.is in no way disturbed.

The above problems do not occur with the small calibration

sensor. The MGL-9 and ACD-2 do not have twinaxial lines. A pair

of semi-rigid coaxial cables lead directly from the sensor to a

connector of SMA type, and since there are no discontinuities, there

should be no oscillations in the frequency response data. An

unfortunate consequence is that the oscillations in the data for the

larger sensors are not removed when the data are calibrated against

data for these smaller sensors.

Compared to the ground plane sensor study, the measurement of

the free-space sensor responses was difficult and frustrating. In

spite of our best endeavors, all of the procedures tried led to noisy

i -52-

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"v .

i.4

Ca) Miniature (b) rcT-lA

Fiqure 23. Twinaxial to dual-coaxial adapters.

ao

-3

C

- .I. .

Page 67: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

data. Whenever a cable was changed or even moved in the chamber, the

oscillations were affected to such a degree that they were no longer

eliminated by the calibration. To obtain data which are, as much

as possible, independent of cable mismatches, and require minimal

disturbance of the sensor in the chamber, it was therefore decided

to separate the measurements into two parts:

(i) angular response measurements,

(ii) frequency response measurements.

In (i) the procedure is to record the data for a variety of e and/or

p, and to normalize these data against the maximum response for that

sensor, e.g., the data for broadside incidence for the ACD sensor.

In (ii) the response is measured only under the maximum signal

condition and normalized with respect to the corresponding response

of the appropriate calibration sensor to determine the frequency

response of the test sensor.

5.3 Angular Response Measurements

The difficulties described above ate up considerable time,

and many measurements were made before usable data were obtained.

5.3.1 ACD-4A(R) Sensor

This was the easiest to measure and was the one studied first.

The sensor rested on a styrofoam pedestal on which a piece of polar

paper was placed to show the sensor orientation, and the two semi-

rigid coaxial leads went up vertically through the roof of the

chamber. Figure 24 shows how the angle e was defined relative to the

-54-

aj

Page 68: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

H

0E

Figure 24 Mesrmn- emtyfr h esr. (h

/-aito rdcsteanua dpl)rsos.

-55

Page 69: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

• _" -, -,.. - , . - .- . . . . . • -. -

direction of the incident electric field, and measurements were

made for e = -90(15)90 degrees. The data were normalized relative

to those for e = 0 and are presented in Appendix A. Thus, for

0 = 0, the normalized amplitude is unity and the phase zero.

5.3.2 MGL-2D(A) and MGL-6D(A)

The geometry is shown in Fig. 25. In contrast to the ACD

sensor, the MGL are not azimuthally independent, and it was therefore

necessary to measure the aximuthal (@) dependence as well as the

e dependence appropriate to the angular or dipole response.

To measure the , variation, the sensor was placed on a

styrofoam pedestal to which a piece of polar paper was attached. The

output leads were taken vertically up through the roof. With gap

No. 1 used as the zero reference for the aximuthal angle 0, data were

recorded for 0 = -90(15)90 degrees with e = 0, and normalized with

respect to the measured data for 0 = 0. The normalized data are

presented in Appendix C.

To measure the angular response, the sensor was rotated forward

through an angle e (see Fig. 25), and a special jig was constructed

to accurately control the tilt angle e. Figure 26 is a photograph

- of the jig with a sensor in place. To permit the bending, a matched

pair of coaxial cables was inserted above the sensor handle (see

Fig. 26), and a braided shield was added to avoid leakage and resonances.

For each sensor, measurements were made for e = 0(15)90 degrees with

= 45 degrees, corresponding to incidence midway between gaps 1 and 2,

*and = 90 degrees, corresponding to incidence on gap 2. The data were

-56-

Page 70: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

=-#1

k k 7

GAP

• 4

Figure 25. Measurement geometry for MGL-serles sensors. (The e-variationproduces angular (dipole) response and p-variation producesazimuthal (constant) response.)

I

-57

Page 71: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

Figure 26. Styrofoam jig used for supportand rotation of MGL-2 and MGL-6sensors. (The incident field isfrom the right-hand side.)

-58-

Page 72: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

normalized with respect to the measured data for the sensor in

question when e = 0, and are presented in Appendix B.

5.4 Angular Response Data Analysis

The measured data were processed according to the formulas

in Chapter 2. For the angular (dipole) response, the quantities

computed are

(i) the dipole response coefficients A (f), from (14);n

(ii) the mean squared angular errorC 2(f), from (15);

(iii) the maximum error ''max(f), from (16).

For the MGL sensors, the following additional quantities were

computed to determine the azimuthal variation of the response:

(iv) the average rotational response coefficient Bn(f), from (17);

(v) the mean squared rotational error 4(f), from (18);

(vi) the maximum rotational error ( maxf), from (19).

Two programs were written, one for each type of calculation, and the

processing and graphics were done on the HP9845 calculator.

Figure 27 shows the angular (dipole) dependence of the response

of the MGL-2D(A) sensor as a function of e with 0 = 45 degrees and

f = 150 MHz. These data were recorded at this one frequency during

the "pre-measurement" stage of the study, and are presented here to

help in understanding the meaning of An(f),0 2(f) and 8 max(f). Thus,

An(f) is the coefficient of the best fit cosine curve, e(f) measures

how closely the curve fits the data, and max(f) is a measure of the

maximum deviation of the data from the curve. The fit in Fig. 27 is

* very good but as the frequency increases, so do the deviations. This

-59-

Page 73: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

L.

- HI

- >1

-J 4

0 U

0 --

'4-

0 L.

.-n #A

C4

-600

-J - - - - -l

Page 74: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

is evident from the subsequent figures where the various quantities

are presented as functions of frequency:

Figures 28 through 32: dipole response for ACD-4A(R);

Figures 33 through 37: dipole response for MGL-2D(A) with

gap No. 1 at =900 ;

Figures 38 through 42: dipole response for MGL-2D(A) with

gap No. 1 at 0 = 450;

Figures 43 through 45: rotational response for MGL-2D(A);

Figures 46 through 50: dipole response for MGL-6A(A) with

gap No. 1 at 0 = 900;

Figures 51 through 55: dipole response for MGL-6A(A) with

gap No. 1 at 0 = 450;

Figures 56 through 58: rotational response for MGL-6A(A).

The implications of the 3-dB frequencies shown in these plots are

discussed in Chapter 6.

-61-

Page 75: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

A, D-4 R iR) D ipc Rrq P - C111

p 1.5i

15 PIR7 12z Li

tt5 gi UP,

500 I~2...c 1 C I)L'UErJI: e MHz .. .

Fgure 28. A n(f) for ACD-4A(R).

-62-

Page 76: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

.. 1

.iC-,l0l8 :F.FqEr

t.- 9 ,.,U

p . r G

1798 MHz

Figure 9. mxf* for ACD-4A(R). 60

"-63

• 02 ,51 .4..,t:: .. , '...L

500 1000_ 1502 jH 5 0 "_ 0 00O ;-s D oo , -.-,i

Figure 9. max f) for ACD-4A(R).e <60

i'

Page 77: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

Al-:.R P'' dIij- Err -'' C

.4I

2 .q 2402 Mliz

- ~ ~ ~ i .17 R 9Z UMi

0 ~~~~j -10 2~u FJ Q.U 05C 3~0 5040FREKU-'ENC~ r MHzI

Fgre 31. 'mx~ for ACD-4A(R), H< 300.

. 3 3dB................................2402 MHz

0 clct2 Iso 1500 e 2500 000 ?SOO 4 0 S '.:'

Figure 32. a x()for ACD-4A(R), e=00.

-64-

Page 78: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

NGML-?DLA,ps9;Dipol* An .sp;rILIJ11

.5

12 PIRF7 92 UPI0

S OOJ "'50 100E017 1250 1500 1150 il00FREOUE14CY 'MHz)

45

12 TR~ 92 UPI

0 250 Soo 7's0 1000 1250I 15 00 1750FPEOUENC ( MHz)

oFigure 33. An (f) for MGL-2D(A), gap No. 1 at =900.

-65-

Page 79: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

I-I

.04

-" P P -- Uri

0 a 5O 00 - 1 011ci 12a i10 oe2CIPFPUA I EtJCY H

Figure 34. 42(f) for MGL-2D(A), gap No. I at 900.

Err .- O.&:- L 1:

II

.2~ . 3dB4932 M4Hz

1 4 1 P I 'r , I

a'.- .250 500] ?5O IO'r¢ _ 12f 1: :,m C.O' 15' *-O'0,-.

Figuur35 34.m (f) for MGL-2D(A), 1eJ 600, gap No. 1 at, g 9oo.r 3. mx

-66-[

Page 80: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

, . ' -V.. -.. . -- - ,

Pis Ef 32 t

•,

" .-J . .

.4-"

3 dB,, , 1215 MHz

"-L3 215ff C, C '50 1 C C 12 15 f C IO0 .0,2

F' ,uE ,: Y MH-z

Figure 36. (f) for MGL-2D(A), gap No. 1 at : 900, IJ < 30'max

rIGL-2ntR--; GEro P .I r r.0: MCLC15

.4

3 dB

.23 1215 MHz

.C 250 50 COO', 1 .O .+ I .. --.

Figure 37. max(f) for MGL-2D(A), gap No. 1 at + : 900, a 00.

-67-

Page 81: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

1-i?1 7~

0

°-...

• .-

LI.H

0I- D5 A0 J5 1000 250 P,--~ I 1Hr

454

WW

-45-.

0 2 Q 0 so 100 1250 1+0 . .50

FRE)UPE: MHz

g0

Figure 38. A(f) for MGL-2D(A), gap No. 1 at 45

-68-

Page 82: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

.03

-J P1J

-92 Uri

3 dB

Fiur f F C o10 1250i 1~J c ic; 1u:5

FRE-DC,:, tl'Hz -

Figure 40.(f) frMGL-2D() , gap No. 1 at 45',O a ..60

-69

Page 83: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

D, N., s E -

.4

A

.2 I'

I , , -" 3 dB.1 .,IIF,...,.'.,i

rji1397 MHz

0 250 5 ' L 5o IH0 I C1250 1.QX1 -cl

f -uH': Hz

Figure 41. 6m (f), for MGL-2D(A), gap No. 1 at 450, < < 300

max

i ' PIL-2D.} 4I;sr41- Err, 3MC L20

.4.."7"

-j

3 dB.1 ~1397 MHz

1 0 1 P sl U1

a 250 5O 0' ,, I "CECl 12d5B0 1 3 1.0I:'F;;'UOIrJC 'r' ,'Mz,

Figure 42. Cmax (f), for MGL-2D(A), gap No. 1 at 450, e = 00.

-70-

Page 84: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

~1-D' Pn F'ct a tt a ri s, r M iLO 1

1.5

Ld

e 1 -----. ,

- I"

C

0 I I I 15 PIR US PI

1-45

0 250 S0 C, E0 1000c 120 1 0 1750CC, C C1-, "--

I,7

I0 IIII I

. r l~~~tGL-2DLFJ ;P,-t~t i.-ar-,al F'esp: M"GLC'?--:

--

I:. ,/r . .... . .. ... . ......

6 n

"i. -71 -

Page 85: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

.~ 04

Figure 44. Cr orML-2DA

NGL-f) MGL-MO(A).

13172-I

Page 86: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

, °..

. cL -RF I-. GF;90.EIII:.:I. A4n: R's £pj r1LOu 1

1.5

•l I l 1 0 i0 CI 'S

F*o E. ~j: P

.

1~~~A :1 L.s- &..~

45

.5

12 PIP a-- UPI

*~~~~ ' 50 10010200200 0 ;SD 4 CC 4SCJK

Kiur 46. A (fIo G-AA a o t 90

0., "'" 'C o '.- -,

-, ------- 4I I I

,- '3 50'-) l 0 150.) 2000C 250 00 :co "-"c0o 4oo3 42C- .JC 7

n

-73-

Page 87: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

E lL _ I ... . .. .IIn , w i. -. .• • pr: E' Ol. L J . , I , _

Cie

.04

LC"

J-1. -; s 0 I- -I

J --,

A Ol

SI

3 dB

2580 MHz

,,, ,, I ; . --- ,'-12 P4IRC G 2 Pqt

-00 1 il 2 C -000 2 500 .O: 00 -5P 0 4': 4 ,'

F" Ekl,:Ei, r Hz

•.. Figure 4. (f) for MGL-6(A), gap No. 1 at . 900 ,Ie < 600.,max

-74-

Page 88: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

L: S90; Mi - r

- - I 1

_j .4

-J , 4 4

4 3 dB. v. 3307 MHz

1:1 5 00 06-ifD 15 0i' _Q -1 2500 . D:0 ce ":E 0 .- 3:

FE!LIEr.r': Y ( Hz

Figure 49. 4max(f) for MGL-6A(A), gap No. 1 at 9o°,lel < 30" .

4 , rl i -

.4 I

S3 dB-j 3307 MHz

a 50 I C10D I .CO 20010 2500 3000 5 0 4 13O% -45;: S7

Figure 50. a(f) for MGL-6A(A), qap No. 1 at 90°, e : 00

-75-

Page 89: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

P.' ;PIiOii

0 ~ -1- tIFF 92 U"t

S' 0U Q D! s 15-30 0002U 2500 1:1L0 -500 4 000 4%

PREOUENCY 'MlHz

45j

I

-451

Soo0 I0 C0Ci ISOO, 2 LIOC 2500 0 00 SSDO 400 'F"RUUNCY rHz

Figure 51. An f for MGL-6A(A), gap No. 1 at 4~450

-76-

Page 90: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

.1

-Ao -

* LIII

* .4

F~~:2880 M Iz

Figure 5 .em x(f) for MGL-6A(A), gap No. 1 at 4509 60

-77-

Page 91: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

m~ ~~~~ - -- - -- - -- .r - . . - • . .

7"6; i -I ,f-s t , - r'!,; L I

1,2 "I2

92 i'

C)C l 0 1' 0 0 4' C I

.8 , *1

N"L.

Fiur 54. ('f fa

--"",4 :N a- Ert . L I !~ i

.4

S3 dB

., 3439 MHz"' al l' i V"f ' r .

J- If l,

12 p-1l; u n 1

a

:.," 1.- ,F G- UP, I

3 -013 1O' 1500 ~030 '500I~ 0 00 : 5 DO 4 0C' 47-1

Figure 54. 6'max(f) for MGL-6A(A), gaps at : 45 lel < 30°

.- 71

: " " I

I /

-:. -i .4 ]

r )

~ ~ .. ,..~ .~.r....>\~j' A', 1 , 3454 M~z

'3-- _ __ __,__ _ _______ _

-0 L i l ,' 1 5 0 2 O0 3' -: S O O :O .'-:5 D O 4 Q,:1 ' ~.).'.

*- Figure 55. m (f) for MGL-6A(A), gaps at , 45, e) = 00.

::: "ax"

.'.. -78-

Page 92: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

2 1

*71.5 I

CL

Cl 50G 1000Cl 1500 26,00 2500 0oo :1500 4000'2FREc'UEIN':y r Hz

4-5

c'i

Ap RP92 L-11

0 5o0 I0. 113 I 00 2500Q C0i l 4000'- 4E577F;El'LIENI: Y MHz

* Figure 56. Bn(f) for IGL-6A(A).

-79-

Page 93: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

r1GL-G fA 1; H~r. Er ri; M.LL02

.02

.02

Figure 57. 2 (f) for MGL-6A(A).

.4

3 dB3256 MHz

CI 51 0~1~ C-RO 25002 345 0 CI SO0 4 ClQ,0 4~

Figure 58. (F.axf for MGL-6A(A).

-80-

Page 94: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

5.5 Frequency Response Data Analysis

The normalization of the data in Section 5.4 eliminated the

effects of many of the cable mismatches, but also removed the true

variation with frequency. We now seek this information for the MGL-2,

MGL-4 and ACD-4 sensors.

With the sensor oriented for maximum signal the response was

recorded for each of the above three sensors as well as for the two

calibration sensors. To minimize any errors resulting from changes in

the equipment and/or chamber, the measurements were carried out in as

short an interval of time as possible. We include here four curves

of more than 60 measurements that were performed for the frequency

response analyses, most of them unacceptable due to the bad oscillations

in data caused by cable mismatches. Once these problems were isolated

and partly circumvented (c.f. Section 5.2) data were recorded and

where appropriate we have averaged (or combined) two sets of data to

produce the curves presented.

Figure 59 shows the response of the ACD-2 sensor normalized with

respect to the MGL-9 response. Both are miniature sensors with 3-dB

roll-off frequencies of approximately 7.5 And 10 GHz, respectively, and

the ratio of their responses should therefore be constant over the

measured range of frequencies. It is not. At low frequenices the ratio

oscillates around the constant value of approximately 1.25 (compared

with the theoretical value of 1.33), but for frequencies exceeding

about 1600 MHz the oscillation is about a linearly increasing function

of frequency. We have no explanation for this increase, and since the

effect of cable losses was eliminated by referencing the responses to the

output terminals at the sensors, the increase cannot be attributed to this.

'" -81-

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For the other (ACD-4, MGL-2 and MGL-4) sensors, the voltages

were referenced to the twinaxial connectors and the phase data

adjusted by adding a constant multiple of the frequency (equivalent

to a delay) to produce the required constant phase at low frequencies.INFigure 60 shows the ratio of the ACD-4 response to that of the

ACD-2. If the latter is presumed linear out to 2000 MHz, the curves

serve to define the frequency response of the ACD-4. At low

. frequencies the measured ratio averages 120 compared with the theoretical

value 100, but decreases starting at about 800 MHz. The 3-dB roll-off

frequency is 1096 MHz, which is consistent with the manufacturer's

specification of >750 MHz. The response of the MGL-2 sensor

normalized to that of the MGL-9 is shown in Fig. 61. The low frequency

ratio is estimated to be 400 and the 3-dB roll-off frequency is 482

MHz. The corresponding values listed by the manufacturer are 500 and

>300 MHz.

Finally, Fig. 62 shows the ratio of the MGL-6 and MGL-9 responses,

and illustrates the type of difficulty encountered throughout this study.

.- The fact is that a twinaxial system (cables, connectors, baluns,

etc.) is not adequate above 100 MHz. The oscillations that are seen

are attributable [6-9] to the MGL-6 geometry, including the handle, and

the other model (serial No. 2) of this sensor showed the same

behavior. The low frequency ratio is estimated to be 40 compared with

the theoretical value 50, and the measured 3-dB roll-off frequency is

1940 (c.f. >1800 MHz).p-2

i, -82-

Page 96: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

,..- A..~.. N,-_.:~~A D- 2 P 1 "FI'L-1- j; ,, .. "

r--i

CL

3 dB2425 MHz

Iia PiR7 r. LJMI

0 10 1,0D 1 000 2EIC .E OI' 0 00 4 OCCt 4s

FRI E J_-'r' (JlC.

.~ - it-i :-s% ,4 , ***.-..V ~.. . ....1

-45

"r 10 PIRR 92 UPI

a S~ C .u; Q C'.J 2O3O 31 2000) :-: 00400

I Figure 59. Response ratio of ACD-2/MGL-9.

-83-

,U

Page 97: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

RCn-4R P "ACD--i -

180 t.4"r'lA"

3 dB1096 MHz

-1 3- 1 P R P

F-;t.'EJEC 'r' , lk z ,

90RCfl-4F I F' R "CD-2t 'F N_-i '

I.- I

jI ,1

-. 0sy~ p ' '. t, ,. ' \1I'',Qf

. , ,,}\ ,, ' ,'

-45

i'' - ,I -- _ _ _ _ _ _:. _' _ •., _ _.',

I. 00 1000 1500 20C1 0

FRECLCIF:V ' Hz

Figure 60. Response ratio of ACD-4/ACD-2.

-84-

il -

Page 98: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

.U L . .......

M L-2 Rj -'lr;L- J t- -

IO0 3 dB482 MHz -

, _ ___- . - - . )

1001

P' E,;uC'1C ' 1 , 1.Hz.

~C

-85

M iL-2DiAi -'_ - - ,-; r1,- .:-!

L.. -

, 10..

L.J

." "1

: Figure 61. Response ratio of MGL-2/MGL-9.

°

',.;:-85-

Page 99: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

RD-Ai27 8i7 MEASURED CHRACTERISTICS OF MULTI-GRP LOOP AND 2/2ASYMPTOTIC CONICAL DIPOLE..(U) MICHIGAN UNIV ANN ARBOR7.i78 V V LIEPA ET AL. MAR 83 Wi?86-i-F RFWL-TR-82-82

UNCLASSIFIED F2968i-8-C-802 F/G 9/i N

Page 100: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

b.9

Ii

11111gig 1L3 28

NATIONAL BUREAU Of STANDARDS-1963-A

- _-_

III:

i

P .. ; : ' .---..' -- . -, 2 " ' , -.-i ' , ... .- .-.-. . -

. ..- _'.

.' -. - . .

.-

. .-

.-.. . . .- - . -. ' ." . ---.' ".- -' --. ' . . " . -

Page 101: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

.r l... .. ........... ...R. A I P

".'

3

194050 M,~

" 45

lm

;L

I-.I...N

u-' ,J ,\) o

S0 Q I ON I : 3 dB l 'I . l lO 1940 tIlz '.

'I 7'

,-.:II)I~i I

k*" " 1~* lti 'E P

,'-" Figure 62. Response ratio of MGL-6/MGL-9.-86

La -86',,I

Page 102: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

6. SUMMARY

U Table 5 summarizes the main conclusions of the study. The first

two columns identify the sensors, and the third lists the minimum 3-dB

roll-off frequencies as estimated by the manufacturer. The remaining

columns contain the information obtained from our measurements. The

fourth column shows the measured 3-dB roll-off frequencies, and in each

instance the value exceeds that given by EG&G [2]. The next three

columns (Columns 5,6 and 7) relate to the angular behavior of the sensors

and list the frequencies at which the patterns deviate from the ideal

(cos e) dipole pattern fitted to angular data in the least squares sense.

The eighth column gives the frequencies at which the azimuthal (rotational)

symmetry breaks down and is applicable only for the MGL free space

sensors. The last column gives the deduced figures of merit as defined

by Baum et al,

'.:": e -"Z] I 2 - -- and 2 f h !0 ZA° I/

0.707 = eq 0.707 Z Aeq ]for electric and magnetic sensors respectively. The 0.707 subscript

indicates that the value is based on the cut-off frequency f of the

sensor (Column 4). In the formulae Zc is the sensor load impedance

(100 ohms) for both the free space and ground plane sensors, Zo is the

free space characteristic impedance, A is the equivalent area as giveneqin the EG&G catalog but doubled for the ground plane sensors, and c

is the velocity of light.

In essence Table 5 shows the frequencies up to which each sensor

. could be used. As already noted, the measured 3-dB roll-off frequency

exceeds the manufacturer's (minimum) specification in each case, but

-87-

Page 103: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

CC

1mJ.

c N f- N 0M

IL N

- 0 *

LL

I. m 6n -- v; 0-,r v

LU i U% .

Lii ~ ~ ~ 0 0U' %L -

MJ. N NmC- NNLnN~

Ef, -5 -.

-c mA LAO

N . sU N ~ U -

14' N NNN N A

ca 0 ~~u 00 S. % A0

IL. .0 . v ?

M,. 'au. f"i -z N

ea'

vi w IvE -j4L1

(J0-88-

Page 104: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

it is also substantially less than the frequencies derived from the

measured angular responses. This suggests that a sensor could, in fact,

be used with confidence at frequencies up to two or three times the

manufacturer's specification, provided the responses were corrected for

the frequency roll-off. In practice, the maximum frequency will depend

on the particular sensor used, and to see this, consider the data for

the MGL-2D(A). The measured 3-dB roll-off frequency is 482 MHz, but

the angular response frequencies are considerably larger. Suppose one

wishes to receive a signal over ±60 degrees range of angle. The maximum

frequency is then 932 MHz, and since this is less than the value in the

last column, the rotational symmetry would still exist. Nevertheless,

to use the sensor at frequencies up to 932 MHz it would be necessary to

correct for the frequency roll-off either with a specially designed

(analog) compensating network or by correcting the measured values when

processing the data.

The study was a classic example of one which is theoretically and

conceptually straightforward, but difficult to accomplish in practice.

The most severe difficulties were encountered with the free-space

sensors that use twinaxial cable systems. Such systems are not effective

above about 100 MHz, and generated oscillation that degraded the accuracy

of our measured data. The high (> 100 MHz) frequency performance of

the free-space sensors merits further study, and we remark that the

performance could be improved if the sensors were designed with twin

coaxial rather than twinaxial output lines.

We understand [10] that the latest versions of the MGL-2 and

MGL-6 ACD sensors have improved impedance matching and extended

frequency range, respectively.

-89-

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7. REFERENCES

[1] Baum, C. E., E. L. Breen, J. G. Giles, J. O'Neill, and G. Sower,

"Sensors for electromagnetic pulse measurement both inside and

away from nuclear source regions," IEEE Trans. Antennas Propagat.,

•I .AP-26, 22-35, 1978.

[2) EG&G, Inc. Catalog, "Standard EMP Instrumentation," Albuquerque,

NM, 87106, 1979.

[3] Stratton, J. A., "Electromagnetic Theory," McGraw-Hill Book Co.,

Inc., New York, 1941.

[4] Baum, C. E. and E. Breen, personal communication, AFWL,

Albuquerque, NM, 87117, 1980.

[5] Senior, T.B.A. and J. Pond, "Pole extraction in the frequency

domain," Radiation Laboratory Final Report No. 017815-1-F,

AFWL Interaction Note 408, December 1981.

[6] Edge], W. R., "MGL-6 B-dot sensor development," EG&G Report No.

AL-1lOl, Albuquerque, NM, 87106, 1974.

[7) Edgel, W. R., "MGL-S7A B-dot sensor development," EG&G Report

No. Al-1104, Albuquerque, NM, 87106, 1974.

[8) Mory, R., P. Anderson, J. Kraemer, and C. Murphy, "Development

and production of multi-gap loop (MGL) Series EMP B-dot

sensors," AFWL-TR-70-153, February 1971.

[9] Olson, S. L. "MGL-S8(R) B-dot sensor development," EG&G Report

No. AL-1187, AFWL-TR-75-252, September 1975.

[10) Prather, W. D., Private communication, AFWL/NTAAT, January 1983.

-90-

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APPENDIX A: ACD-4A(R) DIPOLE RESPONSE DATA (RAW)

Measured data are presented for the ACD-4 sensor as functions

of the frequency for the rotation angles e = -90(15)90 degrees

(see Fig. 1). The data are normalized to the measured values for

e = 0, producing unity plots for e = 0 (see Plot A8). Data for

e = ±85 degrees are also included, but were not used in the analyses

described in Section 5.4.

TABLE Al. LIST OF ACD-4 DIPOLE DATA PLOTS

e (degrees) Plot No. File No.

-90 Al AS 6501

-US A2 AS 6301

*. -75 A3 AS 6309

-60 A4 AS 6317

-45 AS AS 6325

-30 A6 AS 6333

-15 A7 AS 6341

0 A8 AS 6349

15 A9 AS 6357

30 A1O AS 6365

45 All AS 637360 A12 AS 6441

-A12

75 A13 AS 6449mA13

85 A14 AS 6457

90 A15 AS 6473

-91-

Page 107: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

A1.... "A p C~;

1 II-

I I iZ

C U LI O~

Plot Al

-92-

Page 108: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

ZLL

-93

Page 109: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

.,,-_,_.., - t .. . . +.. . -. -. . -. .-._- . -. .- , . ,+.... ,- -,.- ...- . ,-.,./ ++ i+ + : .- ..

. L.--+r

'7m

Aii

4-I94

S- . .-' . - ..

..... ::I..+

!-94

-. . . . . . . .,

Page 110: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

3

2

12 rr2aiu2

Im-

-200

Plot A4

-95-

Page 111: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

PC D4-A-P 4--EC.-------rAC3

LLT-..4

a!u

FP %)',j .=M z)

U

fll

1J 2 1 m J.11

1 OW 2000 303l 4130

F EOUENCY ( MHz)

1:::' I"

Plot -5-96-

'°: Plot A5

• ' -96-

=..

Page 112: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

r . * .r.* -

744-.

"- RCD-4R (R) , -32Cr., VR-VP; R 333

3

2

10 M'i 12 UM

0 I I

0 1000 2000 3000 4000 5000FREQUENCY (MHz)

10ACD-48 ( W, -30fEG, VR-V 1 iRSGI3

50

|U

-50

10 MRY 02 UM

0 1800 2080 2000 4000 500oFREQUENCY (MHz)

Plot A6

-97-

S *o..

Page 113: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

-A :D4( .(P i SDEC.. VAi-VE/; AGG 4 1

-Jt

-PvEC 4 W

12 rPl 91 um~

FFR.uENC Y (Mi-z)

-- 98

Page 114: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

- ~~ ~ P D.~;, OD G. VR--'-S RS6 4----7 '-.-..

0 1000 2000i 2000 4 0 05CEFPEQUENCt' (MHz)

RCD4A (P, , GDEC.,VR'.8 \ FIS-V 49

I:j

0 -LaJ

LT

12 rrcs a1 UPI

0 low0 203000 400 s--

FRE0UE(i*r (M~z)

Plot A8

-99-

Page 115: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

13 FEB ni Uti

FREGiLIEN'CY IkMI-z)

PIC 04 (P I .V A-"VP;ASSS 57

-25

-5

8 00 2 000 3000 4000 5 3

Plot A9

-100-

Page 116: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

4

24

FRE(U~t Ul(Mz)

RC04R), 30DG, VR-VR; RSc -5]

-50

13 rca 81 up

0 1000 2000 3000 4000

FREQL$Ef4Cr tMI-z

Plot A10

6

,:-101-

Page 117: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

* V ,

Plot All

-102-

Page 118: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

7.1

rr.

-103-

Page 119: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

*~~~~~~~7 -r ,. r ij T- 7. --

"...."

-- ..°.. 1 LY ka

,- I-

.., F,,-

. , *-"

Plot A1 3

-104-

Page 120: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

C.O

,% - , -t -

Plt A14 ,

- 1 05 "-*.4 j'"p ip4 VIV . ' i :'p

- ICC

- 1-105-

- * . - ... r- . - ... . " " " Y " " "* " ' ...........................- ,........-.-.............*...

Page 121: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

Il E.: -.

4.j

-5'2 43IC

Plot A15

-106-

Page 122: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

APPENDIX B: MGL-2D(A) AND MGL-6A(A) DIPOLE RESPONSE DATA (RAW)

Measured data are presented for the MGL-2 and MGL-6 sensors as

functions of frequency for the rotation angles a = 0(15)90 degrees

in the dipole response plane. For each sensor, data are shown for

gap No. 1 at = 45 and 90 degrees (see Fig. 25), and all data are

normalized to the measured values for e = 0.

TABLE BI. LIST OF MGL-2 DIPOLE DATA PLOTS

Sap No. 1 at :45' Gap No. 1 at o =9V°

e (denrees) Plot ;!o. File No. Plot N!o. File "o.

0 a1 MG 9165 "C 9357

15 B2 MG 9173 B9 A!G 965

30 B3 MG 9201 B10 MG 9373

45 B4 MG 9209 BI1 MG 9401

60 B5 MG 9217 B12 MG 9409

75 B6 MG 9225 B13 MG 9417

90 B7 MG 9233 B14 MG 9425

TABLE B2. LIST OF MGL-6 DIPOLE DATA PLOTS

Gap io. 1 at = 45" Gap No. 1 at = 90°

e (degrees) Plot No. File No. Plot No. File No.

0 B15 MG 9033 B22 MG 9109

15 B16 MG 9041 B23 MG 9117

30 B17 MG 9049 B24 MG 9125

45 B18 MG 9057 B25 MG 9133

60 B19 MG 9065 B26 MG 9141

75 B20 MG 9073 B27 MG 9149

90 B21 MG 9101 B28 MG 9157

-107-

U

Page 123: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

NMGL- 2DtR J .D E'2LJR;NG9 165

- 0 a

"%,.

10

p4 -

14 CaIC 12 UPI

%'ZO

a 500 18800 158I00

FR OEC -,'z

I,.-

:'.:..Plo Blo t 2 ,,

-1008

14 O! LI

FREUE'v'-:z

.I! -Plot'81L 'G - ,O E',J7 rG .

!1""108-

Page 124: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

h77

MGL-20 1 *I.DE&.34 i'

1.5

2 I-. aI P

se 500 ~ Un

-1109

Page 125: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

- .

+ ''

M GI L** -2 0 .R D E, E I R 1;**2

2 JUN 9 1 UKi

0 .----

5 01000 1500

.r0o

o 8

~.5

-10

rFEI+"rJ:

Plot B

.ii+.110-

Page 126: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

- . . ~ - .- -. - - - - - - - -

-JC'L1rJ:'' M z

u-i

3'UN 0 1 UPI

Ir 200

100 00

F*P.4UE 1-: -

Plot -B4*-

Page 127: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

1.5

LL 1

2 J~JsUN Q; P

F, .,

tIH

-100

2JUN I Ut

Plot B5

-112-

Page 128: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

I .

. ~ ~~~ML-20'(,A ,.-E5DE,;., JRi ,- 2..

a A].

-JJ

I ...J.'

.5.-

(*1* ....

*4 . -i

.].Jut! al uti

S o -0•00 .. 12

' Pl ot B6

100 .- -I13-

....

IE ..-

Page 129: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

-rw "":" ' -" "-:.-" :." .."*~ ** ,7 -. .. W , C, '. r:°" - -" r r"."r-' " 'A i - U" -. • . .

M i;L - 2 D 4C i .I 9 o " E & .2 F, h;,;ll . "- _-

1. 5

s- DO

5* . *---. 3-.-JN g a

-0 iSQ

. ~F 0 0, 100 0 1 10.:,J _

FP E,'J IC r : r IHz200 ' ' ' G 3 R jv ; 1

PI o B7

.100 . . . . .i , .; ",\ '

4i " I'

- 0 I0 0 0!5 0:" ."."5*il;

lI~,-t 'fll

'"; -114-

Page 130: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

HiL- E, -' R. j. ODEC..- w 7P -

1. JUEEl 1~

5 JUN*E 19 1Uj?-o -- s--

13 100 0 1 Sa Q

FPE0ULj'C r MHZ

-10115-

Page 131: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

MiLJ0 A IIDI.J;

-4 JUNT G 1Liti

FPELI;.J A' E EM1.7V, .

101

-I Oxi

4 3JUN 21 Ut'

Plot B9

-116-

'4

Page 132: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

**-2 ' A . . ~ l. .

5 OI I

ML-20(,A20D~i.TAr!,Li?

1 AiN91UP

-20

0- 1 e ) O

F.~ '~R* -AI- 1 r I

Plo B1

Page 133: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

M4L-2OCi A''.45DLI2L. Y;; f;:MZ402I

LJ

00 11ac

Ica

-101

5 2JN I LI ?I

O s CO 1000 15S00CI0F7RQEN~r: r C Ill-

Plot __ -11

L-10

Page 134: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

MGL-2 [If A 7, F4;HL4C9

Cl a

-100

-119-

Page 135: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

D A -LF-L.! , lEI4

I DO

-100

~~CiQ~~ LCIOI) I~)E

r -1-120i

Page 136: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

.'-

~~M,.;L-2 [I , 1 . 0 DE,. .7A, H.I L9-4 2 - c

l I IO.

JN

EL U"

-7

-AJ

C

H

x"ii f, iTI 0

., , y

" JUILNC'1 ui q

Fg[.,>lJ ('. -'2 0 f--t--

Plot B14

-121-

Page 137: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

15

-o -1

".<.9

1 <-J

iCj

U)

1 JLJ. a, Uri ,

"- 0 lOL :000200 300,] 4000 "- -.'

a ac

Plot B15

-122-

Page 138: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

IT,! 1 -

C-1

U..--.

I 3UN 01 1,,

20

-:- . .=

0i 1000 - 000 ~ 00 Q 40 -

Plot B16

-123-

I.°

Page 139: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

- I

* ° ,

, • -

P-11 i D E 1 I JUN t 1,710

1.5

o

L...-.

C .L

CIL L2 A 1 C0

'3 E E O0 +r -LC'C~F'RKE--: PlHz

I

S-. .L/ ,

%'" -1

-- T~~~el ~ JU . I - - . . . L

" i F , : . ........ 2CA C0 7 J4 ¢' -.. _

• -'E .b~t's'- r lPI z

~PlotB17

-124

Page 140: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

R- I *SE YA.r~c

1 .5

*l ri C- 1 0 ... 0Cl

I-

IUL in-

rRL..j1H. t .IH

Plot B18

-125-

Page 141: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

TCA

Ut

-AJ

00

I ILurA Q6 ut.

Vp,,,~~' r%4z

PlotILn- B19E. 1

1006

Page 142: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

I U 9 1021G 'J-. DC ri92

L. -G I 7SD :,. -. ;

-)Jr

CtL

W.4

- 1 JN GJ U1 j0 0002 lc 082 lcl( SOO 400C:

-1271

Page 143: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

IG- -I

I I, N 1) t

1001

-~ IU 2Ut 1 Utlj

~~00 -

I II 0 *c ,.3c I0i"

IdI

~1 00 128-

Page 144: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

PIGL-C.l A -1I. D LEC ]. I. ;

L.5

_____ _____ _ _-I DD ti. Ilip

100

L.J

-100j

0 11 2 000 2000 400 0

Plot B22

-129-

Page 145: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

7J i

SF;RE0uEr-j: e *i uP'

2r3iI-46zut2 1) el 0

-p C L Er K M

Plo 823

-130

Page 146: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

i I C

w'.".

100

LJJ

F;: E ,

-1130

22PR.9 LPIOC OI34OFi: n~: ~

*1L a iJ-I J.DE.,.rA "".;. ."

4 Plot B2

-131

Page 147: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

rI1GL-Rt Ai -I. 45flEG.;;rZil

1.5I. . 1

-100

22 FIR. 6: LI

I C1007 2 CI00 S1000 4t000

FF-E.LIjEIfl:Y OlI M

Plo0B2

10032-

Page 148: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

r1.L',LH-I.60EDE. J. rH;M.4I

I-a

FREO2LIEr'r MIHz

-1130

Page 149: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

I.T7

F-~EU~i: ~ MHz 4JC l~

...................

39 Pig. 91 um

* ~~~- ZOO--- --

C. 000 ~ 2 0 0t320FRE.'IJE+-r Hz

Plot B27

-134-

Page 150: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

-- ~ 7. 7. -G -J -.

I- It

,_.5

I l;--h i- r

1000

I5

-,

Plot B28

-135-

"°a"

'

Page 151: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

APPENDIX C: MGL-2D(A) AND MGL-6A(A) ROTATIONAL RESPONSE DATA (RAW)

The data presented here were obtained for 7 different angles of

rotation of the sensors about their axes, viz € = 0(15)90 degrees.

The angle p is measured from gap No. 2, implying that for o = 0 the

exciting signal is incident on this gap. The data are normalized to

the measured values for 0 = 45 degrees, corresponding to incidence

midway between the two gaps. Because of the symmetry of the sensor

designs, data were recorded over a single quadrant only. Ideally,

the responses should be independent of €, implying unity plots, but

* the results show that this is not the case at high frequencies.

TABLE CL. LIST OF MGL-2 AND MGL-6 ROTATIONAL DATA PLOTS

MGL-2 MIGL-6

(degrees) Plot No. File No. Plot No. File No.

0 Cl MG 9509 C8 MG 9601

15 C2 MG 9517 C9 MG 9609

30 C3 MG 9525 ClO MG 9617

45 C4 MG 9541 Cll MG 9625

60 C5 MG 9557 C12 MG 9633

75 C6 MG 9565 C13 MG 9641

90 C7 MG 9573 C14 MG 9649

-136-

: --;" '' . . . - , ,m ' , - ".

Page 152: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

I I1L-2D if Fi. OIDE?.. JR t,9 ,--

S E Zu-4C10

IO

-:-OctH I - -

I~ ~ ~ -K 3 :

Plot C1

-10137-

Page 153: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

- --- - - - -

1.5

-J~

2 FES a U

Fr. C.,1 I ,:' Hz

plo C

H 138- ~ rL};

IAim

Page 154: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

3 FE -- UI

00 CD~ 15i 00 2 .21

3 FEE I UHif

1200

1 10001C 3ii2 O

Plot C3

-139-

Page 155: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

'2L-:[ ). SD ,; R l;'

2Ji C P - 1

F~RKIJ'Utl-C Y 'Hzl

-1140

Page 156: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

1

" i

FREO".E-CY MHz

lMt 1;L- .. IA p

L.5

-. E - -I:Y ,.H~

• 2~-00 '1i~

rtl

So 1C SOOU. rPLcUErF?! rIH

Plot C5

%':, -141-

,,4

,4

Page 157: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

NMGL-2D1Fi .75DEC. F NR.q- 95

14 OCT 82W1

IMGL-2 0 A 5 DEi. IPIILS 5

3r

-100-

14 Oc r2 fe

Plot C6

'7-142-

Page 158: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

p 1.5

M 1. L 1.'. C.0 D i i;.TR 0!

I OL'

LiA

C100

3 I 9, up

-~0-------- -- 1C

ilHz

Plot C7

-143-

Page 159: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

- ~ ~ ~ ~ ~ G -~ A) -I. DDC. Jn; ..- 7-.- -

DD,; 1 j~qc.96D

I n-I

14 CCT 02 Ufl

a3 1000' 2 Oct 0 l0c00CFREQUENCY fflHz -

~~~t~~~~~cP -_ _ _ _ __ _ _ _ __ _ _ _ _ __ _ _ __8_ _ _ _

-144- ~ - D~.J, L6

Page 160: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

1.71

4

101

1030L0

FREi;-UENC> (MHzI

Plot C9

-145-

Page 161: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

-.7

.5

1I SiU a ] LJm

Z, 00

20M.;L-GAL P i- I ?DE,;. 7P: .~417

100

011)030 2000.100

Plot ClO

-146-

Page 162: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

V7W'E' -F4 F11; -25-

IL!

.5

t, MHz

U 2003

100

'°i

LAJ

-100

IA IUU SX UM

, FR UEN':Y ,AiI44z,~ a 4~c

Plot Cl I

-147-

. . .. - . .. , , . . - . , ,

Page 163: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

MC.L-GI At A I 6 :!DE,. 3I ;

IIc

2100 -

1 clO aI- '

Plot C12

-148-

....................................

Page 164: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

iGL-G4 1 L-i, R "5 DEC TA NGGS-. 4 1

Z/I-I

1 °1

14 OCT 92 UI

00- 1000 21300 C 0 4000

I PI~~GL-G A Aj -i, 75DE,; R;NGSS@41

-A

14 OCT 12 UPI

0 1000 200 a0O0 4000FPCOUEN," Yr M Hz,

Plot C13

-149-

Page 165: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

ILI

4i-

0 10i00 2000 aQ 4000i

-1150

Page 166: CHARACTERISTICS OF MULTI-GAP LOOP MAR smhhhhlohll … · afwl-tr-82-82 afwl-tr-*82-82 measured characteristics of multi-gap * loop and asymptotic conical dipole electromagnetic field

'41'4. e-'4 y

Il

"Aw,

' 4V4

k4 'k

IRV

qy- V4$


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