NRAO Receivers
description
Transcript of NRAO Receivers
Atacama Large Millimeter/submillimeter Array
Karl G. Jansky Very Large ArrayRobert C. Byrd Green Bank Telescope
Very Long Baseline Array
NRAO Receivers
Richard Prestage(Marian W. Pospieszalski, Steve White, Steve Durand)
ALMA Workshop, March 21-22, 2011 2
Noise Temperature Summary of Cryogenic HEMTs
NRAO Cryogenic Amplifiers 3
Mmin Prediction (1991) and State of the Art (2009)
0
5
10
15
20
25
0 10 20 30 40 50
Frequency (GHz)
Nosi
e M
easu
re (K
)
Noise measure at 12.5 K Best Amps.
NRAO Cryogenic Amplifiers 4
VLA/EVLATRx versus Frequency
TRx = m·F + b ; m = 0.5ºK/ GHz ; b = 8ºK
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
0 5 10 15 20 25 30 35 40 45 500
5
10
15
20
25
30
35
40
45
50Simple Noise Model
L-Band 1-2 GHz (Interim)
S-Band 2-4 GHz (N/A)
C-Band 4-8 GHz
X-Band 8-12 GHz (VLA)
Ku-Band 12-18 GHz (N/A)
K-Band 18-26.5 GHz
Ka-Band 26-40 GHz
Q-Band 40-50 GHz
Frequency (GHz)
Rec
eive
r Tem
pera
ture
(K)
L#32(i)
C#20
X#01(t)
K#28
A#07
Q#18
S#01
R. HaywardNRAO, Socorro, NM
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-to-square transition, the square to quad-ridge taper and the quad-ridge 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.
10
Receiver Characterization
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 18-26.5 GHz
warm analog electronics DC – 7.7 GHz (up to 8 dual-polarized beams)
Type II IntegratedDownconverter Module
13
Green Bank, West Virginia, January 11, 2009 14
0.00
5.00
10.00
15.00
20.00
25.00
18.00 20.00 22.00 24.00 26.00
Frequency (GHz)
Nois
e Te
mpe
ratu
re (K
)
043 117 118 125 126 127 128 129 130
131 132 133
GBT K-Band Array Amplifiers at 19 K
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.
15
Compact Corrugated Feedhorns
3.4” O.D. Feedhorns22 GHz Telescope Beams
16
Thermal Gap
17
• 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
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 1st 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 FunctionsPCB Side MMIC Side
23
Snakes of Star Formation
26
The Galaxy is rich in Snakes of star forming clouds:
Finn and Jackson, in preparation.
KFPA NH3 (1,1) contours on Spitzer Glimpse Image
Langston, Batistti, Jones 2011, in preparationAlso see posters by Batistti et al and Jones et al
28
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