NRAO Receivers
Richard Prestage
(Marian W. Pospieszalski, Steve White, Steve Durand)
Atacama Large Millimeter/submillimeter Array
Karl G. Jansky Very Large Array
Robert C. Byrd Green Bank Telescope
Very Long Baseline Array
Noise Temperature Summary of Cryogenic HEMTs
ALMA Workshop, March 21-22, 2011
2
Mmin Prediction (1991) and State of the Art (2009)
25
Nosie Measure (K)
20
15
10
5
0
0
10
20
30
40
50
Frequency (GHz)
Noise measure at 12.5 K
Best Amps.
NRAO Cryogenic Amplifiers
3
VLA/EVLA
EVLA Project Book - TRx Requirements (Band Center)
TRx versus Frequency
Band
L
S
C
X
Ku
K
Ka
Q
TRx
14
15
16
20
25
34
40
48
50
Simple Noise Model
45
L-Band 1-2 GHz (Interim)
S-Band 2-4 GHz (N/A)
Receiver Temperature (K)
40
C-Band 4-8 GHz
X-Band 8-12 GHz (VLA)
35
Ku-Band 12-18 GHz (N/A)
K-Band 18-26.5 GHz
30
Ka-Band 26-40 GHz
25
Q#18
Q-Band 40-50 GHz
20
X#01(t)
15
L#32(i)
A#07
10
5
K#28
C#20
S#01
0
0
5
10
15
20
25
30
35
40
45
50
R. Hayward
NRAO, Socorro, NM
Frequency (GHz)
TRx = m·F + b ; m = 0.5ºK/ GHz ; b = 8ºK
NRAO Cryogenic Amplifiers
4
The RF Signal Path
• The Feedhorn:
– Compact
corrugated
horn.
The RF Signal Path
• A top view of the 15K cold
plate and RF signal path:
– The input to the cryostat.
– The charcoal trap, the
heaters and the
thermostat.
The RF Signal Path(cont.)
• The thermal gap and
OMT assemblies:
– Foam window.
– Gap set to 5mils.
– The full assembly
forms the circular-tosquare transition, the
square to quad-ridge
taper and the quadridge to coaxial
sections.
The RF Signal Path(cont.)
• The RF Tree:
– Thermal gap/RF choke.
– Ortho-mode transducer.
– 90°Quadrature hybrid
coupler.
– Cryo-isolator and calibration
coupler.
– Three stage NRAO Cryo-3
InP HFET low noise amplifier.
Receiver Characterization
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K Band Focal Plane Array
(Shanghai)
Steven D. White*, Matt Morgan, Felix J. Lockman,
Eric Bryerton, Glen Langston, Roger Norrod, Bob
Simon,Galen Watts, Sivasankaran Srikanth, Gary
Anderson
System Baseline Specifications
Specification
Requirement
Frequency Band
18-26.5 GHz (complete K-Band coverage)
Can tune up to 27.5 GHz
Instantaneous RF Bandwidth
1.8 GHz (front-end) as built
Number of Beams
7
TRX (each beam, not including sky)
<25K (75% of band)
<35K (entire band)
Aperture Efficiency
>55% (any pixel)
Polarization
dual, circular (axial ratio <= 1dB)
Polarization Isolation
>25 dB
Pixel-to-Pixel Isolation
>30 dB
Headroom
>30 dB (to 1 dB compression point)
12
Bandwidth Limitations
Sub-Assembly
Total Potential Bandwidth
Comments
cold-electronics
(feed, OMT, LNAs...)
>8.5 GHz
degrades outside of 1826.5 GHz
warm analog electronics
DC – 7.7 GHz (up to 8 dualpolarized beams)
Type II Integrated
Downconverter Module
13
GBT K-Band Array Amplifiers at 19 K
Noise Temperature (K)
25.00
20.00
15.00
10.00
5.00
0.00
18.00
20.00
22.00
24.00
26.00
Frequency (GHz)
043
117
118
131
132
133
125
126
127
128
129
130
Green Bank, West Virginia,
January 11, 2009
14
Feedhorn Arrangement
• GBT:
• 36” mounting ring on the receiver
turret would support about 60 KBand feedhorns.
• 3.45” spacing (~2.5 HPBW)
• Shanghai:
• Feed Design.
• Efficiency ?
• Spacing?
• Mechanical Impact.
15
Compact Corrugated Feedhorns
3.4” O.D. Feedhorns
22 GHz Telescope Beams
16
Thermal Gap
0.543" circular waveguide
0.010" gap with choke groove
upper half at 300 K, lower at 15 K
hollow, shaped G10 supports
optimized for weight, strength,
and thermal isolation
• Cuming Microwave PS-102 foam
for vacuum seal
• Cuming Eccobond 45 epoxy
• 3-mil Kapton vapor seal
•
•
•
•
•
17
Quadrature Phase Shifter and OMT
18
Noise Calibration Source Integrated
With Coupler
19
KFPA Uses Existing EVLA Low-Noise
Amplifier Design
20
Gapped WR42 Sliding Waveguide Output
Transition
•
•
•
•
•
0.360” maximum travel
∆ length on cool-down: ~0.144”
Stable at final temperature
Chomerics 1285 conductive
elastomer
Ecco-foam PS102 with 3 mil Kapton
21
Sliding Waveguide/Thermal Gap Assembly
Thermal Gap and 20 cm SS waveguide: 1.7 Watts 1 st Stage Load.
30 cm SS coax: 0.54 Watts 1st Stage Load.
Total: 1st Stage 18 W; 2nd Stage 3 W.
Contraction from 300K to 15K is ~ 4.1 mm of total 6.35 mm.
Downconverter Size Dominated by DC
Control Functions
PCB Side
MMIC Side
23
Snakes of Star Formation
KFPA NH3 (1,1) contours on Spitzer Glimpse Image
The Galaxy is rich in Snakes of star forming clouds:
Finn and Jackson, in preparation
.
26
Langston, Batistti, Jones 2011, in preparation
Also see posters by Batistti et al and Jones et al
The National Radio Astronomy Observatory is a facility of the National Science Foundation
operated under cooperative agreement by Associated Universities, Inc.
www.nrao.edu • science.nrao.edu
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