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EM COMPONENTSUPDATE & PERFORMANCE RESULTS
S. Srikanth
Critical Design Review
GBT K-Band Focal Plane Array
January 30-31, 2009
OUTLINE OF TALK
1. Feed – Measured Results
2. Array Performance
3. Efficiency Comparison
4. Phase Shifter – Measured Results
5. OMJ – Measured Results
KFPA FEED
Frequency 18-26.5 GHzFeed taper -13 dBCompact/Profile taper hornRing-loaded corrugations
Aperture ID = 2.93”* (5.5λ22)OD = 3.4”Length = 6.658”Pitch = 0.082” (λ18/8)Vane = 0.026”Depth = 0.13” (0.28λ26.5)69 corrugationsΘi = 8º ; Θmax = 17º*ID of linear taper horn=5.55”
Measured Patterns & Taper
H-plane; z=-2.975
-60
-50
-40
-30
-20
-10
0
-60 -45 -30 -15 0 15 30 45 60
Azimuth (deg.)
Am
pli
tud
e (d
B) 18
20
22
24
26
28
Freq.
(GHz)
H-pln
(dB)
E-pln
(dB)
18 -11.7 -11.2
19 -12.6 -12.3
20 -13.2 -13.6
21 -13.7 -14.2
22 -13.7 -14.2
23 -13.5 -14.0
24 -13.2 -13.6
25 -13.0 -13.4
26 -13.0 -14.3
26.5 -13.9 -14.7
Avg. -13.2 -13.5
E-plane; z=-2.975
-60
-50
-40
-30
-20
-10
0
-60 -45 -30 -15 0 15 30 45 60
Azimuth (deg.)
Am
pli
tud
e (d
B) 18
20
22
24
26
28
22 GHz; Theory & Measured
22 GHz; H-Plane
-60
-50
-40
-30
-20
-10
0
-90 -60 -30 0 30 60 90
Angle (degrees)
Ampl
itude
(dB) Theory
Measured
22 GHz; E-Plane
-60
-50
-40
-30
-20
-10
0
-90 -60 -30 0 30 60 90
Angle (degrees)Am
plitu
de (d
B) Theory
Measured
H-plane E-plane
Measured Cross-polarization in 45 deg. plane
45 deg. plane; Cross-pol.
-80
-70
-60
-50
-40
-30
-20
-10
0
-90 -60 -30 0 30 60 90
Azimuth (deg.)
Am
plit
ud
e (d
B) 17
17.4
18
19
20
45 deg. plane; Cross-pol.
-80
-70
-60
-50
-40
-30
-20
-10
0
-90 -60 -30 0 30 60 90
Azimuth (deg.)
Am
plit
ud
e (d
B)
21
22
24
25
45 deg. plane; Cross-pol.
-80
-70
-60
-50
-40
-30
-20
-10
0
-90 -60 -30 0 30 60 90
Azimuth (deg.)
Am
plit
ud
e (d
B)
26
27
28
29
Measured Input Return Loss
GBT K-band array receiver feeds
-50
-40
-30
-20
-10
0
17 19 21 23 25 27
Frequency
Ret
urn
Lo
ss (
dB
)
# 01
# 02
# 03
Ø36.00"
Azimuth/Asym.plane
Elev./Symm. plane
LAYOUT OF ELEMENTS (61 Feeds)
Element spacing 3.45”1+6+12+18+24
22 GHz; Telescope beams in Azimuth (asym.) planeHPBW = 34”
X” Throw
(arcsec)
Throw
(HPBW)
0 0 0
3.45 94 2.7
6.9 189 5.5
10.4 284 8.2
13.8 378 11.0
17.3 473 13.7
Azimuth beams; 0,1,2-0.63; 3-0.62; 4-0.59; 5-0.55
20
30
40
50
60
70
80
90
-0.1000 -0.0500 0.0000 0.0500 0.1000 0.1500 0.2000
Azimuth (deg)
Am
plit
ud
e (d
B)
0
3.4
6.92
10.4
13.9
17.3
Beam throw 27.4”/inch; 0.43HPBW/λ
* Theoretical feed patterns used
22 GHz; Telescope beams in Elevation (symm.) planeHPBW = 34”
y” Throw
(arcsec)
Throw
(HPBW)
0 0 0
6 164 4.8
12 331 9.6
18 498 14.5
Elevation beams; 0,1-0.63; 2-0.62; 3-0.60,
20
30
40
50
60
70
80
90
-0.1000 -0.0500 0.0000 0.0500 0.1000 0.1500 0.2000
Elevation (deg)
Am
plit
ud
e (d
B) 0
6
12
18
Beam throw 27.4”/inch; 0.43HPBW/λ
* Theoretical feed patterns used
Circle #1 (3.4”rad): 62.9% min.
Circle#2 (6.9”rad): 62.9% min.
Circle#3 (10.4”rad): 61.7% min.Circle#4 (13.8”rad): 58.9% (az) -6.3%; 61.6% (el) -2%
Circle 18.0” rad: 54.7% (az); 60.2% (el)
FEED OFFSET & APERTURE EFFICIENCY
Aperture Eff. Vs Feed offset; 22 GHz; OD=3.4"
0 3 69
12 15
18
0.5
0.52
0.54
0.56
0.58
0.6
0.62
0.64
0 5 10 15 20
Offset (inch)
Eff
icie
ncy Asym
Sym
Ø36.00"
Azimuth/Asym.plane
Elev./Symm. plane
-2%; measured -5% at 8.4”offset
Ø36.00"
Elev./Symm. plane
62.9%
61.7%
58.9%54.7%
58.9%
61.5%
Optimum orientation of Elements
62.9%
61.7%
54.7%
60.7%
60.7%
61.4%
62.9%
61.7%
54.7%
60.7%
60.7%
61.4%
Beam width & Beam spacing
Freq.
(GHz)
HPBW Beam Spacing
(HPBW)
18 40” 2.3
22 34” 2.7
24 31” 3.0
26.5 29” 3.2
Element spacing 3.45”; Beam spacing 94arcsec Beam throw 27.4 arcsec/”
Measured 20 GHz; E-plane
-70
-60
-50
-40
-30
-20
-10
0
-90 -60 -30 0 30 60 90
Angle (degrees)
Po
wer
(d
B)
Prof
LinL
Measured 20 GHz; H-plane
-70
-60
-50
-40
-30
-20
-10
0
-90 -60 -30 0 30 60 90
Angle (degrees)
Po
wer
(d
B)
Prof
LinL
KFPA FEED Vs. 20 GHz FEED
Measured patternsKFPA Feed – Profile Horn (-13.5,-13.3 dB)20 GHz Feed – Linear Taper Horn (-11.7,-12.8 dB)
GBT Beam; Sym. plane; 20 GHz
20
30
40
50
60
70
80
90
-0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08
Angle (degrees)
Po
we
r (d
B)
Lin
Prof
GBT Beam; Sym. plane; 18 GHz
20
30
40
50
60
70
80
90
-0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08
Angle (degrees)
Po
we
r (d
B)
Lin
Prof
GBT Beam; Sym. plane; 22 GHz
20
30
40
50
60
70
80
90
-0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08
Angle (degrees)
Po
we
r (d
B)
Lin
Prof
Freq.
(GHz)
Linear taper Profile ήapl- ήapp
------------------
ήapl
(%)
Edgetaper (dB)
ήapl Edge taper (dB)
ήapp
18 -12.64 0.6995 -11.45 0.6965 0.43
20 -12.23 0.7284 -13.41 0.6560 9.94
22 -14.07 0.6888 -13.95 0.6189 10.15
KFPA FEED Vs. 20 GHz FEEDTelescope beam patterns, Efficiency
Measured 24 GHz; E-plane
-70
-60
-50
-40
-30
-20
-10
0
-90 -60 -30 0 30 60 90
Angle (degrees)
Po
wer
(d
B)
Prof
LinH
Measured 24 GHz; H-plane
-70
-60
-50
-40
-30
-20
-10
0
-90 -60 -30 0 30 60 90
Angle (degrees)
Po
wer
(d
B)
Prof
LinH
KFPA FEED Vs. 24 GHz FEED
Measured patternsKFPA Feed – Profile Horn (-13.7,-13.3 dB)24 GHz Feed – Linear Taper Horn (-12.1,-13.1 dB)
GBT Beam; Sym. plane; 22 GHz
20
30
40
50
60
70
80
90
-0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08
Angle (degrees)
Po
we
r (d
B)
Lin
Prof
GBT Beam; Sym. plane; 24 GHz
20
30
40
50
60
70
80
90
-0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08
Angle (degrees)
Po
we
r (d
B)
Lin
Prof
GBT Beam; Sym. plane; 26.5 GHz
20
30
40
50
60
70
80
90
-0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08
Angle (degrees)
Po
we
r (d
B)
Lin
Prof
Freq.
(GHz)
Linear taper Profile ήapl- ήapp
------------------
ήapl
(%)
Edgetaper (dB)
ήapl Edge taper (dB)
ήapp
22 -12.10 0.6770 -13.95 0.6189 8.58
24 -12.58 0.6669 -13.48 0.6050 9.28
26.5 -12.46 0.6456 -14.32 0.5864 9.17
KFPA FEED Vs. 24 GHz FEEDTelescope beam patterns, Efficiency
S. Srikanth, “A Wide-Band Corrugated Rectangular Waveguide Phase Shifter for Cryogenically CooledReceivers”, IEEE Microwave and Guided Wave Letters, Volume 7, pp. 150-152, June 1997.
18-26.5 GHz Phase Shifter
0.474 x 0.452; Length 4.84”
Serial #01; Return Loss; Perp. 0.474
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
17 18 19 20 21 22 23 24 25 26 27
Frequency (GHz)
Ret
urn
Lo
ss (
dB
)
S11
Serial #01; Return Loss; Perp. 0.452
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
17 18 19 20 21 22 23 24 25 26 27
Frequency (GHz)R
etu
rn L
oss
(d
B)
S11
MEASURED RETURN LOSS
Serial #01; Insertion Loss; Perp. 0.474
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
17 18 19 20 21 22 23 24 25 26 27
Frequency (GHz)
Ret
urn
Lo
ss (
dB
)
S11
Serial #01; Insertion Loss; Perp. 0.452
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
17 18 19 20 21 22 23 24 25 26 27
Frequency (GHz)
Ret
urn
Lo
ss (
dB
)
S11
MEASURED INSERTION LOSS
Serial # 01; Differential phase
65
70
75
80
85
90
95
100
105
110
115
17 18 19 20 21 22 23 24 25 26 27
Frequency (GHz)
Dif
fere
nti
al p
has
e (d
egre
es)
Delta
Serial # 03; Differential phase
65
70
75
80
85
90
95
100
105
110
115
17 18 19 20 21 22 23 24 25 26 27
Frequency (GHz)D
iffe
ren
tial
ph
ase
(deg
rees
)
Series1
MEASURED DIFFERENTIAL PHASE
ORTHO MODE JUNCTION
E. Wollack, “A Full Waveguide Band Orthomode Junction”, EDIR No. 303, NRAO, May 16, 1996
WR42 waveguide; 4.5” x 2.8”Septum 0.010” (Beryl. Cu)Pin 0.040” dia. (Beryl. Cu)
353 Leaded brass; Weight 1 lb
ORTHO MODE JUNCTION
6061-T6 Aluminum; Weight 0.33 lb
6061-T6 ALUMINUM Vs. 353 LEADED BRASS
Property 353 Leaded Brass 6061-T6 Aluminum
Composition
(%)
Cu 62, Pb 1.8, Zn 36.2
Al 97.92, Si 0.6, Mn 0.28, Mg 1.0, Cr 0.2
Density
(lb/in3)
0.307 0.098
Thermal conductivity
(BTU/ft. h.°F)
104 96
Coeff. of thermal expansion
(ppm/°C)
18.4 23.6
Electrical Resistivity
(μΩ.cm)
6.6-3.5 5.0-4.0
K-Band OMT S/N 35 - Insertion & Input Return Loss(RHH : 20 Feb 2008)
-1.0
-0.9
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
18 19 20 21 22 23 24 25 26 27 28
Frequency (GHz)
Ins
ert
ion
Lo
ss
(d
B)
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Re
turn
Lo
ss
(dB
)
IL - Main Arm
IL - Side Arm
RL - Main Arm
RL - Side Arm
Measured S-parameters- Brass OMJ
Measured by R. Hayward, NRAO, Socorro, NM
Main arm Side arm
Measured S-parameters- Aluminum OMJ
Measured by R. Simon, NRAO, Green Bank, WV
#1: 18 GHz; #2: 26.5 GHz; #3; 27.5 GHz
CONCLUSION
All EM components have been validated.
Feed: 3 nos.
Phase shifter: 2 good ones; 6 being electroformed
OMJ: 3 nos. of aluminum OMJ
Circular-rectangular transition, 45 twist: 10 nos of each being processed.
Pc 3”-4.2”
22-26.5 Feed: ID=4.54 OD=4.85 L=8.14 pc=5.9
Phase patterns & Phase centers
H-plane; z=-2.975
-80
-60
-40
-20
0
20
40
60
80
-30 -20 -10 0 10 20 30
Azimuth (deg.)
Pha
se (d
eg.)
17
17.4
18
19
20
21
H-plane; z=-3.627
-80
-60
-40
-20
0
20
40
60
80
-30 -20 -10 0 10 20 30
Azimuth (deg.)
Ph
ase
(deg
.)
20
21
22
23
24
H-plane; z=-4.126
-80
-60
-40
-20
0
20
40
60
80
-30 -20 -10 0 10 20 30
Azimuth (deg.)
Ph
ase
(deg
.)
24
25
26
26.6
27
28
PC at 18 GHz
PC at 22 GHz
PC at 26 GHz
Aperture Efficiency & System Temperature
3.4 “ OD Feed 2.8” OD Feed
Freq
(GHz)
Ap.Eff. System Temp
(K)
90 30
G/T (K/Jy)
90 30
Freq
(GHz)
Ap.Eff System Temp
(K)
90 30
G/T (K/Jy)
90 30
18 0.6911 54.9
6.7
62.1
7.1
0.0358 0.0317 18 0.7006 58.5 66.0 0.0341 0.0302
22 0.6287 45.6
4.9
63.3
5.3
0.0392 0.0283 22 0.6500 47.2 65.0 0.0392 0.0284
26.5 0.5900 42.2
4.1
55.5
4.3
0.0398 0.0302 26.5 0.6131 41.1 54.3 0.0424 0.0321
Tspill