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EVLA FEEDS DESIGN. S. Srikanth NRAO/Charlottesville. VLA Cassegrain Geometry Drawing. Current Receiver Bands. VLA Vertex Feed Cone. EVLA Receiver Bands. Selection of Bands. Minimize number of receivers Use existing technology - PowerPoint PPT Presentation
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S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
EVLA FEEDS DESIGN
S. SrikanthNRAO/Charlottesville
VLA Cassegrain Geometry Drawing
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Current Receiver Bands
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
VLA Vertex Feed Cone
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
EVLA Receiver Bands
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Selection of Bands
• Minimize number of receivers
• Use existing technology
• Performance at the band edges - feeds, polarizers, amplifiers etc.
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Selection of Feed Type and Parameters
• Nominal taper of -13 dB at 9.25 degrees
• Compact horns where space is limited
• Ring-loaded slots (except for Q-band)
• Number of corrugations/wavelength - 3.8
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Conventional Corrugations
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Ring-Loaded Corrugations
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
VSWR – Conventional and Ring-Loaded
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Linear Taper Horn 75" OD – 1.0 GHz
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Linear Taper Horn 75" OD – 1.4 GHz
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Comparison of 75" OD and 62" OD Feeds
Feed Taper at 9 Degrees (dB)75" OD 62" ODFreq.
(GHz) H E X H E X 0.85 -5.0 -3.4 -19.0 -3.7 -6.6 -14.1
1.0 -6.8 -7.3 -5.1 -4.81.1 -8.7 -8.1 -6.0 -5.81.2 -10.0 -10.0 -7.2 -7.01.4 -10.3 -11.3 -10.0 -9.91.6 -11.0 -10.5 -10.2 -11.41.8 -9.4 -11.0 -10.5 -9.92.0 -10.5 -11.6 -12.4 -12.12.3 -8.5 -9.0 -9.0 -9.7 -22.4
1-2 GHz Average taper -10.0 dB1-2 GHz Average taper - 9.3 dB1.2-2 GHz Average taper -10.2 dB
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Compact Horn – 75" OD 1.0 GHz
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Compact Horn – 62" OD 1.0 GHz
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Compact Horn – 75" OD 1.4 GHz
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Compact Horn – 62" OD 1.4 GHz
VLA Cassegrain Geometry Drawing
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
ANALYSIS METHODOLOGY
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
ANALYSIS METHODOLOGY
= /max = /sinmax
6. Grids on the reflector surface
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Comparison of Subreflector Patternsat 1.5 GHz ( = 0°)
JPL Software NRAO Software
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Comparison of Subreflector Patternsat 1.5 GHz ( = 90°)
JPL Software NRAO Software
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Comparison of Main Reflector Patterns
at 1.465 GHz
Measured
NRAO Software -4 -2 0 2 4
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Subreflector Scatter Pattern – 1.4 GHzCompact Horn - 75" OD
Symmetric Plane
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Subreflector Scatter Pattern – 1.4 GHzCompact Horn - 62" OD
Symmetric Plane
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Subreflector Scatter Pattern – 1.4 GHzCompact Horn - 75" OD
Asymmetric Plane
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Subreflector Scatter Pattern – 1.4 GHzCompact Horn - 62" OD
Asymmetric Plane
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Subreflector Scatter Pattern – 1.4 GHzCompact Horn - 62" OD
Symmetric Plane
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Subreflector Scatter Pattern – 1.4 GHzCompact Horn - 62" OD
Asymmetric Plane
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Main Reflector Pattern – 1.4 GHzCompact Horn - 75" OD
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Main Reflector Pattern – 1.4 GHzCompact Horn - 62" OD
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Comparison of 75" OD and 62" OD Feeds
Effc. 75" & 62" OD Feeds
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4
Frequency (GHz)
Eff
icie
nc
y
75" OD
62" OD
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Compact Horn –75" OD
Spillover Temp. 75" OD
0
10
20
30
40
50
0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4
Frequency (GHz)
Ts
pill
(K
) Elev.90
Elev.60
Elev.30
Elev.20
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Compact Horn – 62" OD
Spillover Temp. 62" OD
0
10
20
30
40
50
0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4
Frequency (GHz)
Tsp
ill
(K) Elev.90
Elev.60
Elev.30
Elev.20
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Comparison of 75" OD and 62" OD Feeds
Gain/Tsys. 90 deg.
0
0.1
0.2
0.3
0.4
0.5
0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4
Frequency (GHz)
G/T
(1/J
y*10
E-2
)
75: OD
62" OD
Trx=8
Tsk=4,6
Tsc=2,3
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Comparison of 75" OD and 62" OD Feeds
Gain/Tsys. 60 deg.
0
0.1
0.2
0.3
0.4
0.5
0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4
Frequency (GHz)
G/T
(1/J
y*10
E-2
)
75" OD
62" OD
Trx=8
Tsk=4,6
Tsc=2,3
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Comparison of 75" OD and 62" OD Feeds
Gain/Tsys. 30 deg.
0
0.1
0.2
0.3
0.4
0.5
0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4
Frequency (GHz)
G/T
(1/J
y*10
E-2
)
75" OD
62" OD
Trx=8
Tsk=4,6
Tsc=2,3
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
The hybrid lens feed
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Measured Pattern – Current Feed
E-1.53 GHz (raw)
-45-40-35-30-25-20-15-10-505
-100 -50 0 50 100
Angle (deg)
Lev
el (
dB
)
#20;-18.6
#2;-17.4
#4:-17.6
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Corrected Pattern – Current Feed
E,1.53 GHz;Avg.
-45
-35
-25
-15
-5
5
-100 -50 0 50 100
Angle (deg)
Lev
el (
dB
)
Raw;-17.9
Prcd;-12.5
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Measured Pattern – Current Feed
H-1.53 GHz (raw)
-45-40-35-30-25-20-15-10-505
-100 -50 0 50 100
Angle (deg)
Lev
el (
dB
)
#20;-18.7
#2;-18.7
#4;-20.7
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Corrected Pattern – Current Feed
H,1.53 GHz;Avg.
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
5
-100 -50 0 50 100
Angle (deg)
Le
ve
l (d
B)
Raw;-19.4
Prcd;-13.0
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Comparison: New Design & Current Feed
L-Band
Efficiency
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.5 1 1.5 2 2.5
Freq. (GHz)
Eff
icie
ncy
New
Current
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Comparison: New Design & Current Feed
L-Band
Current Feed
0102030405060708090
100
0.5 1 1.5 2 2.5
Freq. (GHz)
Tsy
s (K
)
Elev. 90
Elev. 60
Elev. 30
Elev. 20
Trx=8
Tsk=4,6
Tsc=2,3
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Comparison: New Design & Current Feed
L-Band
New Design
0102030405060708090
100
0.5 1 1.5 2 2.5
Freq. (GHz)
Tsy
s (K
)
Elev. 90
Elev. 60
Elev. 30
Elev. 20
Trx=8
Tsk=4,6
Tsc=2,3
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Comparison: New Design & Current Feed
L-Band
Elevation 90
00.05
0.10.15
0.20.25
0.30.35
0.40.45
0.5
0.5 1 1.5 2 2.5
Freq. (GHz)
G/T
(1/J
y*10
E-2
)
New
Current
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Comparison: New Design & Current Feed
L-Band
Elevation 60
0
0.1
0.2
0.3
0.4
0.5
0.5 1 1.5 2 2.5
Freq. (GHz)
G/T
(1/
Jy*1
0E-2
)
New
Current
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Comparison: New Design & Current Feed
L-Band
Elevation 30
0
0.1
0.2
0.3
0.4
0.5
0.5 1 1.5 2 2.5
Freq. (GHz)
G/T
(1/
Jy*1
0E-2
)
New
Current
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Comparison: New Design & Current Feed
L-Band
Elevation 20
0
0.1
0.2
0.3
0.4
0.5
0.5 1 1.5 2 2.5
Freq. (GHz)
G/T
(1/
Jy*1
0E-2
)
New
Current
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Subreflector Scatter Pattern – 3.0 GHz-11 dB Taper
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Subreflector Scatter Pattern – 3.0 GHz-18 dB Taper
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Gain/Tsys Analysis
Effic. at 3 GHz
0.5
0.55
0.6
0.65
0.7
0.75
0.8
-20-18-16-14-12-10
Taper (dB)
Eff
icie
nc
y
Efficiency
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Gain/Tsys Analysis
Tsys. ; 3 GHz
0
10
20
30
40
50
-20-18-16-14-12-10
Feed Taper (dB)
Ts
ys
. (K
)
Elev. 90
Elev.60
Elev.30
Elev.20
Tr=13
Tsk=4,6
Tsc=2,3
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Gain/Tsys Analysis
G/Tsys ; 3 GHz
0
0.1
0.2
0.3
0.4
0.5
-20-18-16-14-12-10
Feed Taper (dB)
G/T
(1
/Jy
*10
E-2
)
Elev. 90
Elev.60
Elev.30
Elev.20
Tr=13
Tsk=4,6
Tsc=2,3
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
EVLA – Predicted Performance
S. Srikanth EVLA Feed/FE PDRFebruary 12-13, 2002
Future Work
1. Gain/Tsys vs. feed taper analysis at 10
GHz and 30 GHz.
2. Effect of phase center travel on pointing.
3. Optimization of the feed pointing.
1. Gain/Tsys vs. feed taper analysis at 10
GHz and 30 GHz.