1. NRAO Receivers Richard Prestage
(Marian W. Pospieszalski, Steve White, Steve Durand)

2. Noise Temperature Summary of Cryogenic HEMTs
ALMA Workshop, March 21-22, 2011

3. Mmin Prediction (1991) and State of the Art (2009)
NRAO Cryogenic Amplifiers

4. VLA/EVLA TRx versus Frequency
EVLA Project Book - TRx Requirements (Band Center)
Band L S C X Ku K Ka Q
TRx 14 15 16 20 25 34 40 48
TRx = m·F + b ; m = 0.5ºK/ GHz ; b = 8ºK
NRAO Cryogenic Amplifiers

5. C-band Receiver System Specifications: Receiver noise temperature: 16K
4/16/2017
C-band Receiver
System Specifications:
Receiver noise temperature: 16K
Receiver gain, output power and headroom: 60dB, -31dBm, 33dB
Input Return Loss: <15dB
The calibration noise temperature: 1.3K and 13.0K
InP HFET bias data: supplied from CDL
Cold station temperatures two stage: 50K and 15K

6. 4/16/2017
The RF Signal Path
The Feedhorn:
Compact corrugated horn.

7. 4/16/2017
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.

8. The RF Signal Path(cont.)
4/16/2017
The RF Signal Path(cont.)
The thermal gap and OMT assemblies:
Foam window.
Gap set to 5mils.
The full assembly forms the circular-to- square transition, the square to quad-ridge taper and the quad- ridge to coaxial sections.

9. The RF Signal Path(cont.)
4/16/2017
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.

10. Receiver Characterization

11. 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

12. System Baseline Specifications
Requirement
Frequency Band
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)

13. Bandwidth Limitations
Sub-Assembly
Total Potential Bandwidth
Comments
cold-electronics
(feed, OMT, LNAs...)
>8.5 GHz
degrades outside of GHz
warm analog electronics
DC – 7.7 GHz (up to 8 dual-polarized beams)
Type II Integrated
Downconverter Module

14. GBT K-Band Array Amplifiers at 19 K
Green Bank, West Virginia, January 11, 2009

15. Feedhorn Arrangement GBT:
36” mounting ring on the receiver turret would support about 60 K-Band feedhorns.
3.45” spacing (~2.5 HPBW)
Shanghai:
Feed Design.
Efficiency ?
Spacing?
Mechanical Impact.

16. Compact Corrugated Feedhorns
3.4” O.D. Feedhorns
22 GHz Telescope Beams

17. 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

18. Quadrature Phase Shifter and OMT

19. Noise Calibration Source Integrated With Coupler

20. KFPA Uses Existing EVLA Low-Noise Amplifier Design

21. 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

22. Sliding Waveguide/Thermal Gap Assembly
This receiver incorporates two thermal transitions to reduce loading of the cryogenic refrigerators. A unique feature of this receiver is a sliding transition. As all components must conform to the shadow of the feed, each pixel is long and slender (~42”) with considerable the contraction of metal occurs during cooling. A sliding waveguide assembly provides the relief.
Estimated thermal coefficient of expansion considering aluminum components with TCE of 22 x 10^-6 m/m K and length L = 0.66 m, delta T = 285 gives 4.1 mm. With order centimeter wavelengths this change is significant. Compensation for this compression during cooling must be accomplished by either short rigid stainless steel waveguide, SS coaxial cable bent to flex, a waveguide gap similar to the thermal transition, or a flexible waveguide. Paramount to the method chosen is baseline stability considerations. Flexible waveguide is known to have stability problems while SS coaxial cable presents stability problems to a lesser extent. For improved stability, development and testing thermal transition techniques, or other unknown options is required.
Thermal Gap and 20 cm SS waveguide: 1.7 Watts 1st Stage Load.
30 cm SS coax: 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.

23. Downconverter Size Dominated by DC Control Functions
PCB Side
MMIC Side

26. 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.

27. Langston, Batistti, Jones 2011, in preparation
Also see posters by Batistti et al and Jones et al

28. www.nrao.edu • science.nrao.edu
The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
• science.nrao.edu