1960 IRE TRANSACTIONS ON MILITARY ELECTRONICS 527

Electronically Tunable Circuit Elements*SAMUEL STIBERt

Summary-During the past sixty years, attempts have been made which the selective circuit is moved past the signals.to develop electronically-controllable circuit elements to be applied By countermeasures receivers is meant a receivinigto filter networks in tunable receivers and transmitters. Both thepolarization of the dielectric material used in the construction of system to be used against noncooperative signals. Al-

capacitors and the permeability of the ferrite core material used in though countermeasures receivers have much in com-inductor design, lend themselves to electronic variation; in fact, the mon with conventional receivers, the signals which theychange in the incremental permeability of a magnetizable material are intended to intercept, being of an unknown char-in the presence of a superimposed varying magnetic field was pat- acter, call for wide RF bandwidths, the utmost in sensi-ented as early as 1901. Usable circuit elements, however, were notrealizable for application in the frequency ranges above 100 kc, nor y ldid the available materials provide the desired characteristics for types for equipment economy and high probability ofmodern filter design of receivers and transmitters. intercept. RF sweep ranges are generally as wide as the

USASRDL initiated a program in 1948 to investigate the prob- state of the art will permit. Rapid scan is often desirablelems associated with electronically variable inductances. New ferrite and sometimes it is required that the RF band bematerials were developed and a better understanding of the -over-all scanned within the time duration of a single pulse. Inproblem obtained. This program grew in magnitude, calling upon theefforts of both universities and commercial organizations, in addition addition to rapidly sweeping wide RE bandwidths, it iSto the internal effort within this laboratory. The outcome is a family often also necessary to scan inarrower RE bands, and toof controllable inductances, electronically tunable in the frequency positioll these narrow bands anywhere within the RFrange dc to 500 Mc with reasonable Q's, power requirements, and banid. In addition, particularly for counitermeasuressmall in size and weight. Large frequency variations are obtainableand they are usable under environmental conditions of temperature, applications, electronic tuning permits the sweep of RFhumidity and vibration encountered in field conditions. With these frequency to be stopped quickly oni receipt of a signial.electronically tunable inductors the military now have available re- Thus, the advantages of an auxiliary high speed, mlulti-receivers which can be remotely tuned, rapidly scanned over fre- functioni (pulse-width and PRF) signial analyzer can bequently ranges of better than two-to-one and stopped quickly on fully realized by stopping the receiver on the signal ofreceipt of a signal. They can sweep large frequency ranges and pre- interest without mechanical overshoot. Thesent a full panoramic display of the signal environment present inm pnorameach range, together with a simultaneous expanded sector display receiver is also capable of sweeping the entire signalof the signals of interest. range, thus presenting a full panoramic display of the

This paper discusses fundamental considerations and definitions signal environment present in that range, together withof ferromagnetic, ferroelectric and back-biased devices. It describes a simultaneous expanded sector display. A review of thethe problems involved in the development of the electronically con- Itrollable inductance, provides a discussion of requirements this de- abv . q

vice must meet, and gives operating characteristics of inductors de- menits utilizing tmechanical slidinig or contacting struc-veloped. Applications of the device in military equipment are dis- tures are not acceptable. Rapid rotation of conventiolnalcussed, some examples of their use in receivers described and some capacitors, butterfly structures, split cylinder filters anldtypical circuits provided. A comparative evaluation of ferromagnetic, capacitive loaded coaxial cavities have all beeni tried andferroelectric and back-biased diode tuning devices completes this rejectedpaper.reetdi

In additionl to the above requiremenits, the idealI. INTRODUCTION tuning element should be capable of operation to 1000

T HIS IAPER grew out of studies of conitrollable Mc with a usable Q for use in amplifier or oscillatorcircuit elemenits for use in couintermeasures pail- circuits. It should have a low temperature coefficient oforamic receivers. By panoramic reception is meant frequency from -40'C to +850C. It should be small,

I ~~~~~~~compact and capable of large-scale mianiufacture withthe reception of signals within a band of frequencies p gand the display on a visual indicator of the presence and onlY a small fraction of rejects. It should be capable ofcharacter of these signals. There are, in general, three frequenicy scan over a ratio of four to one or better, withmethods of panoramic reception: 1) that in which the relatively small control power anid with low voltage.signal frequencies are swept in succession past a rela- To meet these requiremetnts, the countermeasureslnar a seti cci s a l egineers within USASRDL sposored a study adtlvely~~ ~ ~ ~ ~ ~ ~ ~ ~ inet atiow-nn ofecvmethods ofostuin aiedattheaov

output is used to actuate a visual indicator, 2) that in inetgato ofmtoso ulg, amda h bvwhich the signal frequencies are applied simultaneously requirements, anld a task2 was placed with the Engineer-to a number of selective circuits of adjacent frequencies inlg Research Institute, at the University of Michigan,and the outputs applied either simultaneously or inl Annl Arbor. Some of the iiiformuation contained in thisrapid succession to a visual indicator, and 3) that in

I S. Stiber, "Survey of tuning systems in the frequency rangeabove 300 mcs," presented at Symp. on Countermeasures Intercept,

* Received by the PGMIL, July 11, 1960. LCS 56/1 RDB, pp. 233-262; July 15, 1948.t USASRDL, Fort Monmouth, N. J. 2 Task #24. Contract DA-36-039 sc 63203.

528 IRE TRANSACTIONS ON MILITARY ELECTRONICS October

paper resulted from this task. In addition, contracts of dc control power are required. Over the useful rangewere placed with various commercial organizations for of up to 16 volts, the capacity varies inversely with thethe development of materials, tuning elements and pro- square root of the bias voltage. A variationi of capacitytotype receivers. These firms are listed in Section IV. from 160 to 25 .m,uf was obtained.

Silicon diodes: In the case of a silicon junction diode,II. DEFINITIONS AND FUNDAMENTAI the density of charge carriers at the p-n junction (elec-

CONSIDERATIONS trons in the n-region and holes in the p-region) is re-

Ferromagnetic Devices duced to almiost zero as the voltage is applied in thereverse direction across the diode. This regioni of zero

In the simplestform, the tuning elementconcharge densltv, known as the depletioni region, is riotferrite core containing two toroidal windings. The wind- mmerelxl- swept clear of charge carriers but actuallying to be controlled is called the signial winding and the I

widens as the reverse bias iS increased. In effect, theother is the control winding. By varying the currenit in two conducting areas appear to act as two metal platesthe control winding, we change the magnetic field acting which tend to move further apart with increase inon the core material and, in turn, the inductance of the voltage. The plate area and the dielectric constant re-signal winding. The core material in general exhibits a main the same. It is important in application that 11owide variation of permeability with applied field. Aclass of magnetic ferrospinels or ferrites have enjoyedethepromiiience in this field because of their high to the junction to become positive. This occurrenice is

usuallv avoided by the placing of two back-biased(103 to l0O ohms/cm) and freedom from eddv current diodes in series oppositionl across the tanik coil.loss. The ferroelectric mode of operationi is extremely dif-Ferroelectric Dev-ices ferenit. Barlium titanate (BaTiO3) is mixed with a non-

ferroelectric buffer material such as stronitium titanateThe ferroelectric tuning element is a capacitor whose

value can be changed bv an applied voltage. In general,n eoe utbeiitra.Tebru iait

valueIcan be changed by an applied voltage. Jn general, is made up of a multitude of tiny particles whose spon-the voltage applied to the capacitor plates results in .s.ta change in the dielectric constant of the material be- t do a raverage of the orientationis is zero. When a dc bias is

applied to the material, some of the dipoles will alignsidered as representative of materials suitable for elec- themselves in the field, resulting in a decrease in thetronic tuning. For miaximum tuninig range, materials dielectric constanit of the material. As the biasing fieldshowing the largest change in E with applied electric is further increased, more and more dipoles are reori-field E, are desired. When a large electric field is applied e.ted until saturation is reached. Minimum capacitanceto a ferroelectric material, it is driven into saturation occurs when the device has maximum bias applied. Un-or maximum polarization. In a practical situation, the like the back-biased diode, the ferroelectric capacitorlimit of E is generally determined by the electric break- ca be biased either negative or positive. The perform-downi field of the specimeni. Unique to ferroelectric ance of the diode capacitor shows only a slight depend-tuning is the problem of producing thin sheets of titanate ence upon temperature, whereas that of the ferro-dielectric having apparent honmogeneous properties. electric is quite sensitive to temperature.Local impurities in thin specimens are very noticeable, Fig. 1 shows a typical capacity vs voltage curve ateven tending to produce electric breakdown. The chiefdifficulty with ferroelectric tuninig is that of obtaining capacitor andvalso,yfor Mpan arHug back-large tuning ratios together with low temperature sensi- biased diode.tivity.

Back-Biased Diodes Ill. THE DEVELOPMENT OF THE CONTROLLABLEINDUCTANCE (FERROMAGNETIC TUNING)

Variable capacitance germanium diode: A semiconduc-I

tor when biased in the reverse direction (nonconduction) Requirementsis a capacitance which can be varied by the bias voltage. In summary, the ideal controllable inductance should:Giacoletto and O'Connielli have described such a diode. 1) Have low loss, high resistivity (103 to 109 ohmsThe diode consists of a 0.02-inch dot of indium, alloyed cm)on a 0.002-inch-thick wafer of n-type germanium and 2) Have zero temperature coefficient of frequency vsmounted with low inductance connections. temperature from -50°C to +100°C.

Typically, the performanlce with 6-volt bias is as 3) Be small, compact, light-weight.follows: a capacitance of 38 ,u,f, a capacitive change of 4) Be capable of large-scale manufacture at low cost.3 ,tyif per volt, a Q of 17 at 500 Mlc. Only microwatts 5) Have controllable inductance ratio of 100 to I at

10 kc to 4 to 1 at 1000 Mc.

3L. J. Giacoletto and J. O'Connell, RCA Rev)., vol. 18, pp. 66- 6) Require small control power.85;'March, 1956. 7) Provide a linear sweep with voltage variation.

1960 Stiber: Electronically Tunable Circuit Elements 529

ACTUAL VALUES100 100% CAP. I100% BIAS I TEMP. E

DIODE 25 PF 130 VOLTS 270C r -90 FERROELECTRIC 125 PF 170 VOLTS 27°C I I

80

70- M V)60- UNIVERSITY OF MICHIGAN FERROELECTRIC CAPACITOR

' 50 \

30 -\ HUGH HC 7001 Fig. 2-1938 controllable inductance.Q ACK BlIASED DIODE

20- +B

10 AW | AB

20 60 100 140 180 220 260BIAS (5)

Fig. 1-Typical capacity vs voltage curves at 100 Mc (normalized). -H J H3 +H

Ferromagnetic Tuning Prior to 1948 /

de Kramolin' described a new tuning device which he /aH H3-Hsaid was especially suitable for remote control. Briefly, 2/.Yit consisted of varying the inductance of a tuning coil ___-B $AA ABAHby changing the permeability of its powdered-iron core.This was accomplished with the aid of an electromag- Fig. 3-Definitions of magnetic parameters.

net, varying the current through its field coil. Fig. 2 actually concerned in magnetic tuning is the incremen-illustrates this early tuner. The high-frequency pow- tal permeability .AA.This is the per.eability observeddered-irotn core m of low permeabilltv lies between the when the specimen is subjected to a combined ac andpoles of the outer magniet E. The path of the biasing dc field, both applied in the same direction. This isflux is inidicated by the arrow w. The RF coils are illustrated in Fig. 3, which gives definitionis of magneticwound in opposite directioins on the pressed-powder cupcore. Thus, the signial current produced n1o charge in parameters. M changes with both bias field Ho and ac

iniductance by its biasing effect. The iniductance varia- field H.Figs. 4 and 5 will further illustrate the definlitionstion is thus totally a functioni of the field control win-d- wich. follow.which follow.ing. It is initeresting to niote that, at the same time, I t

' .. . . ' ~Iinitially the flux deiisity rises rapidlvl as the coiitrolSiemers and Hulse were experimietitntig in Berlin with c isimilar configurations for remote electronic tuning. In suration of.thecferrite iseachieved.iInrthe iall stagethe period 1941-1945, work in this field was continuedin various laboratories in Germany. Approximately five there exists a flux density B, which corresponids to a

control currenit i, and at this poinlt the slope of thewatts was required to produce an inductance variation B-H curve is given by the tangent Ti. Now we applyof niie to one. de Kramolin suggested using a permanent an ac to the signal winding (whose amipere tunes aremagnet bias to reduce the power requirement. He small compared to the control winding). The apparentdescribed ai application in which the electronicall permeability of the ferrite core (that is the signal core)tuned coil was made the filter elenment of a TRF re- i

5~~~ ~ ~ ~ ~ ~ ~~~~i1S B//,AH Fqor snmall values of AH, this perimeabilityceiver.5is very nearly the slope of the tanigent Ti previously

Fundamental Definition and Considerations definied. The iniductance of the signial winiding is directlyFor maximiiumi inductance charge, a large charge in proportionial to the incremental permeability AB/AH.

core permeabily is d . RIf we now apply ani inicrease in control current i2core permeability iS desired. Regardless of the initial II 1 1 II1.. .. . . ...................we will produce in the ferrite core a seconld larger fluxpermeability, it iS theoretically possible for us to obtainl..' . . .. . ~~~~~B2.Looking at the B-li curve in1 Fig. 4, it should bea permeability approaching unilty by driving the speci-men nto aturtio. Threfoe, oe souldlookfornoted that the slope T2 is smaller thanl Ti. The inlduct-

materials wit inta hihereailt. Th.uatt ance of the signal winding willl have decreased by the2 # ~~~ratio of T2/T1. As we further inlcrease the control current

the slope continues to decrease to T3, at which pointL. de IKramolin, Wi/reless World, vol. 42, pp. 160-162; February saturation of the ferrite core has been reached and we

24, 1938.wilhvacivdamnmmidcaceiourdo5L. de Kramolin, Wireless World, vol. 42, pp. 186-188; March 3,wl aeahee iiunutneiu ai

1938. frequency or signal winding.

530 IRE TRANSACTIONS ON MILITARY ELECTRONICS October

ul 2 : 7r/lL 0 UN

B5~~~~~~~~~~~~~~~~T

T [ C / CIRCUIT CAP. 30 uuf

O ni ~~~~~nij iec ec e

CONTROL AMP. T/UN IT LENGTH I3ec =LENGTH OF MAGNETIC CONTROL PATH 3L

F;ig. 4-Incremental permeability tuning showing ideal |B-H curve for ferrite core. 2

2~ ~ ~~~~~~~~~~~~2

Bs

/T | AB 2 x , , ,175 AMP.TRTURNSBI 0-7 ]fo.51.0 1.5 2.0 2.5 AMP

5 / / t l lCONTROL CURRENT

/ 0 I ~~~~~~~~~~~~Fig.6-General Ceramics material G.

0 1 72 IcTMAX

Fig. 5 Effect of hysteresis. RR.F. WIINDINGFERRITE CORE

l'he above simplified presentation lacks inclusion of (a) ( BIAS WINDINGthe hysteresis effect. Because of the hysteresis phenom- 9ena in the ferrite material, the flux density is not a singlefunction of the control current. The typical behaviorof a ferrite is shown in Figs. 5 and 6. Although the hys- COTTROL WINDINGteresis effect to be described in negligible compared toeddy current losses in the signal region, it plays a very R.F.WININGsignificant part in receiver circuit design FERRITE COREAs the control current is varied, as shown in Fig. 5,

from zero to maximum and back to zero, the flux of (b) TRANSFORMER COREthe ferrite will vary but on the return half-cycle willalways be higher than that which corresponded to the JJJsame control current on the previous half-cycle. Actu-lally, when the control currenlt is returned to zero, the CONTROL WINDINGcontrol flux does not vanish but a residual control flux gR.F. WINDINIGB remains. Fdr either manual or rapid sweep, it is then _XFRIECRnecessary to blank out one half of the magnetization (c) llTRANSFORMER IRON COREcycle (Fig. 7). A TUl

Material ConsiderationsThe most important component of the controllable CONTROL WINDING

inductor is themanetcateiausdnteFig. 7-Typical forms of tuning elements.

-llUCO1S ih ant ae1lue ntecorMAX

ing. Ferrites have been used exclusively. Some of theproblems in using ferrites are described below:

1960 Stiber: Electronically Tunable Circuit Elements 531

1) Magnetostriction. At the mechanically resonant TABLE Ifrequency, the inductor will experience a severe loss in PERFORMANCE OF FERRITES; CONTROLLABLE REACTORSQ. This condition is present in many low-frequency Frequency Ratio Q Controlmaterials such as Philippe 4E and in Stackpole 1819. Material Range, Mc Ratio Q Current

2) Instability. When control current is applied it is Ceramag 0.4-6.3 15.7 20 0-50 mafound that several minutes may be required for the 27signal winding inductance to stabilize. Examples are Ceramag 0.75-5.1 6.7 50-100 0-60 maStackpole's Ceramag 7A, Ferricore's C, and in General 9Ceramics, Q body material. Ceramag 9-39-0 4.35 50-80 0-50 ma

3) Lack of uniformity in core mnaterial. Considerable 5451variability exists amonig cores of anly batch of ferrites. Phillips 20-45 2.25 70 0-150 maGenerally, tracking of such cores is obtained bv means 2285of a bias winding in addition to the cenitral winding. Gen Ceramics 5-26 5. 16 22-46 0-50 maSince the core materials vary in initial permeability, Ferramic Qthe bias currents are adjusted to reduce the initial MF 2728 35-76 2 35-60 0-30 mapermeability of the higher permeability cores down tothe lowest permeability core in the batch of control-lable inductors to be tracked. In order to track at thehigh end, adjustmenit mllust be made of the control wind-ing at or approaching core saturation. pounds, and required approximately five watts controlA most (lesirable procedure is to test each core, de- power to produce an inductance variation of nine to

magnetize it, anld tlhen mileasure its permeability and one in the frequency range up to several hundred kc.select cores close in initial permeability. Beyond this frequency, its losses became excessive. The

4) Shielding problems. It is niecessary that capacitive C.G.S. No. 81 AMI inductor can be tuned electronicallycoupling betweeni the signal and control windings be over a 64 to one iniductanice range, from 50 to 400 Mc.minimized. Capacitive couplinig reduces the effective Q It requires only mils of control current, weighs a fewof the inductor. A useful solution, particularly at low ounces, and is lost behind your thumb. Such devicesfrequency, is the use of a good electrostatic shield be- are in use in missiles, telemetry and in general VHFtween signal and control windinigs. and UHF low-power applications. Signal windings can

5) Manufacturing problems. In addition to obtaining hanidle up to eight watts; however, additional increduc-a ferrite core of the desired electrical characteristics, tor units capable of handling several hundred watts atthere is the problem of obtainiing uniform atnd conisist- frequenicies betweeni 50 and 100 Mc have been con-ent properties. Core materials supposedly of the same structed.make-up vary from batch to batch and from month to Successes with ferroelectrics have been somewhatmonith. The ferrite manufacturer has a difficult problem marginal, particularly because presently availablein control of raw materials a small difference in the materials appear to dissipate too much energy forpurity of raw oxides has a profound effect on the varia- application to microwave frequencies. A more thoroughtion of product impurities. Even the dust from previous understanding of the loss mechanism for these sub-operations which lines the floor influences the make-up stances is required. Stanford University has an effortof new batches of materials. Matching of cores may underway in their Electronics Laboratory at Palo Alto,require large waste or shrinkage because of elimination Calif. onl a new capacitor which has a significantlyof nonusable cores. After proper selection of the core greater range of capacitance variation. It is called thethere is the cost of machining, core testing and match- M-O-S, or metal-oxide-silicon, capacitor. The M\-O-Sing. To this must be added the cost of winding, assem- capacitor gets its extended range by going to higherbling and final testing. capacitance per unit area at low voltage. This results

from the fact that in the M-O-S capacitor the zero biascapacitance is determined by the thickness of the oxide,which in practice can be made of the magniitude of a

IV. A LOOK AT THE FUTURE hundred angstroms, while the zero-bias capacitance ofThe story of the development of the controllable in- the p-n junction is determined by the inherent width

ductance, the ferroelectric capacitor and the reverse- of the depletion layer, which mnay be of the order ofbias diode is part of the story of the "fabulous fifties." several thousand angstroms.Contrast de Kranliolin's inductor of 1938 with that ex- The 1960-1970 period should see a considerable in-hibited at the 1960 IRE International Convention, in crease in system utilizationl of all of these devices toNew York, byTRAK Electronics Co. (formerly C.G.S.), provide remote conltrol, electronlic tunling, rapid fre-WVilton, Conn. de Kramolin's device weighed several quenlcy scanl, etc.

532 IRE TRANSACTIONS ON MILITARY ELECTRONICS October

Commercial organizations in the 1950-1960 period High Permittivity Ferroelectrics," WVillow Run Labs., Univer-sity of Michigan, Ann Arbor; January, 1960.

received support in these fields, mainly from govern- 17] "Study Development and Production of Ferrospinels Applicablement agencies. The Signal Corps at Fort Monmouth, to Tuning of Search Receivers," Electronic Defense Group,

University of Michigan, Ann Arbor, Progress Rept. No. 12;N. J., has been particularly active in the support of June, 1956.the controllable inductance for use in electronic warfare [81 Samuel Stiber, "Use of ferromagnetic materials in electronic

tuning of radio frequency components," Proc. Natl. Electronicsequipments. Commercial organizations most active have Conf., Chicago, Ill., September 29-October 1, 1952, vol. 8,been TRAK Electronics Company (formerly C.G.S. pp. 462-469; January, 1953.

F. Wagenknech, "Electric and magnetic properties of ferromag-Laboratories); A.R.F. Products, Inc., River Forest, Ill. netic and iron (lI)-oxide in high frequiency alt. field," Kolloid-Vari-L Company, Inc., Stamford, Conn.; anid Genieral Z., vol. 112, No. 1; 1949.

[10] A. L. Mikailyan and A. A. Pistol'kors, "Electromagnetic wavesCeramics Corporationi, Keasbey, N. J. in magnetized ferrite in the presence of conducting planes,"

Radiotekhnika, vol. 10, pp. 14-25; 1955.REFERENCES [111 C. G. Sontheimer, "Applications of high frequency saturable

reactors," Proc. Natl. Electronics Conf. Chicago, Ill., September,[11 L. J. Giacoletto, "Junction capacitance and related character- 1953, vol. 9, pp. 299-310; February, 1954.

istics using graded impurity semiconductors," IRE TRANS. ON [12] F. C. Gabriel, "Controllable inductor characteristics," Electro-ELECTRON DEVICES, vol. ED-4, pp. 207-216; July, 1957. mechanical Design, pp. 10-14; M4arch, 1956.

[2] T. Butler, Jr. and G. A. Roberts, "A Tabulation of Voltage- [131 F. C. Gabriel, "Ferrite inductors tuLne panoramic receiver,'Variable Capacitors," Electronic Defense Group, University of Electronics, vol. 29, pp. 169-172; August, 1956.Michigaii, Ann Arbor, Tech. Memo No. 70; April, 1959. [14] H. WV. Katz, "Small signal application," in "Solid State Magnetic

[31 E. GelBard, "Magnetic Properties of Ferrite Materials," Tele- and Dielectric Devices," John Wiley & Sons, Inc., New York,Tech. & Electronic Inds., pp. 50-52; May, 1952. N. Y., ch. 5; 1959.

141 E. Albers-Schoenberg, "Ferrite Compounds with More Than [151 "An Introduction to Increductor Controllable Inductors,"Three Oxide Components," Cream. Age; May, 1952. C.G.S. Labs., Wilton, Conn.

[51 D. M. Grimes, "Study of Circuit Applications of Solid State [161 A. Kaufmann, "Circuit design with controllable inductors,"Devices to ECM Equipment," Electronic Defense Group, Uni- Electronic Design, pt. I, April, 1954; pt. II, vol. 26, pp. 186-versity of Michigan, Ann Arbor, Progress Rept. No. 16; Febru- 188; May, 1954.ary, 1960. [171 S. Stiber, "Remote tuning receiver has no moving parts,"

[61 H. Diamond, "Polarization, Microwave Dispersion and Loss in Electronics, July, 1953.

The Signal Corps' Contribution to the Microwave Antenna Art*LEONARD HATKINt, MEMBER, IRE

Summary-This paper contains a brief summary of the Signal tions industry were constructing bigger and betterCorps' contribution to the antenna art. Emphasis is on the post towers and rhombics in order to improve the quantityWorld War II period and on microwave antennas. Only develop- .

q

ments which have had reasonably wide application are discussed. ad q ity ofemessagesothatdcould betrasitteradio. W7ith the advent of radar and the increasing useTpHE popular image conjured up by the term "ani- of higher frequencies, the trend and tempo of antenna

tenna" has undergone a rather dramatic revi- developments changed markedly. Radar required rela-sion since the days of the founding of the Signal tively narrow beams at VHF and UHF frequencies,

Corps. At that time an antenna meant an appendage to thus leading to the development of fairly complex broad-an insect's head and, indeed, the wagging of the signal side arrays of radiating elements.flags which was among the more reliable means of The standard search radar set of pre-World War IIcommunication in those days was somewhat reminis- and early war years was the SCR-2 70, whose anteninacent of the vibrations of the insect's antennas which, of 32 dipoles became a landmark familiar to manyour entomologist friends tell us, are used for a variety a G.I. Broadside array construction of that periodof purposes from food-finding to courtship in the insect reached a culmination in the "Diana" Radar located atworld. the Evans Signal Laboratory which, in early 1946,

During the early days of radio communication, while electrified the world with the news of radar contactthe elders among us were wreaking havoc with interior with the moon. The antenna to launch the wave thatdecorating schemes by stringing long wires through the first made contact with an extra-terrestrial object con-house, or attaching wires to bedsprings in order to im- sisted of 64 dipoles and provided for that time, a phe-prove the reception on our crystal detector sets, Signal nomenal gain of 21 db in the mid-VHF region. Fig. 1Corps personnel and their colleagues in the communica- is a photograph of this antenna.

\Vith the opening up of the microwave region, theentire field of microwave optics was available for exploi-* Received by the EGMIL, July 11, 1960. tto.A hs ihfeunis ovninlatna

t USASRDL, Fort Monmouth, N. J. ail.Athshihfeune,cov toa nens