Download Receiver System Centimeter Regime

Centimeter Receiver Design
Considerations
with a look to the future
Steven White
National Radio Astronomy Observatory
Green Bank, WV
Todd. Hunter, Fred. Schwab. GBT High-Frequency Efficiency Improvements,
NRAO May 2009 Newsletter
Performance Limitations
• Surface (Ruze λ/16)
–
–
ξ = 50%
300 µmeters → 63 Ghz
• Atmosphere e-t t = optical depth
• Spill Over Ts
• Pointing
• Receiver Noise Temperature (Amplifier)
TR
Frequency Coverage
• 300 Mhz to 90 Ghz
• l: 1 meter to 3 millimeters
• l < 1/3 meter - Gregorian Focus
• l > 1/3 meter - Prime Focus
Gregorian Subreflector
Reflector Feeds
Profile: L (size), S (size), Ka (spacing), KFPA (spacing), Q (spacing)
Linear Taper: C, X, Ku, K
Design Parameters: Length (Bandwidth), Aperture (Taper, Efficiency)
GBT
α= 15º , Focal Length = 15.1 meters, Dimensions = 7.55 x 7.95 meters
Optimizing G/T
Prime Focus Feed
Cross Dipole 290-395 MHz
Gregorian Feeds
S, Ku (2x), L
W band feed
KFPA Feed
140’ Prime Focus and Cassegrain Feed
140’ & 300’ Hybrid mode
prime focus
Radio Source Properties
•
Total Power (continuum: cmb, dust)
– Correlation Radiometer Receivers (Ka Band)
– Bolometers Receivers (MUSTANG)
•
Frequency Spectrum (spectral line, redshifts, emission, absorption)
– Hetrodyne
– Prime 1 & 2, L, S, C, X, Ku, K, Ka, Q
•
Polarization (magnetic fields)
– Requires OMT
– Limits Bandwidth
•
Pulse Profiles (Pulsars)
•
Very Long Baseline Interferometry (VLBI)
– Phase Calibration
Prime Focus Receivers
Receiver
• PF1.1
• PF1.2
• PF1.3
• PF1.4
• PF2
Frequency
0.290 - 0.395
0.385 - 0.520
0.510 - 0.690
0.680 - 0.920
0.910 - 1.230
Trec
12
22
12
21
10
Tsys
46 K
43 K
22 K
29 K
17 K
Feed
X Dipole
X Dipole
X Dipole
Linear Taper
Linear Taper
Gregorian Receivers
Frequency Band
[GHz]
•
•
•
•
•
•
•
•
•
•
1-2
L
2-3
S
4-6
C
8-10 X
12-15 Ku
18-25 K
22-26 K
26-40 Ka
40-52 Q
80-100 W
Wave Guide Band
[GHz]
OMT (Septum)
OMT (Septum)
OMT (Septum)
OMT (Septum)
12.4 -18.0
18.0 - 26.5
18.0 - 26.5
26.5 - 40.0
33 - 50.0
75 to 110
Temperature
[º K]
Trec
Tsys
6
8-12
5
13
14
21
21
20
40-70
20
22
18
27
30
30-40
30-40
35-45
67-134
~ 3 10^-16
W/√Hz
Receiver Room Turret
Receiver Room Inside
Polarization Measurements
• Linear
– Ortho Mode Transducer
– Separates Vertical and Horizontal
• Circular
– OMT + Phase Shifter (limits bandwidth)
– 45 Twist
– Or 90  Hybrid to generate circular from linear
Linear Polarization
Orthomode Transducer
Circular Polarization
A Variety of OMTs
K band OMT
Equivalent Noise
Amplifier Equivalent Noise
Amplifier Cascade
Input Losses
HFET Noise Temperature
Radiometer
Correlation Radiometer
(Ka/WMAP)
1/f Amplifier Noise
MUSTANG 1/f Noise
HEMT 1/f Chop Rates
Amplifier νo
[GHz]
(band)
Δνrf
[GHz]
fchop(ε =.1)
[Hz]
Δνrf (ε = .1,
f = 5 Hz)
[GHz]
L
1.5
0.5
0.8
3
C
4.0
1
2
2
X
10
3
7
2
Ka
30
10
80
0.6
Q
45
15
375
0.2
W
90
30
1500
0.1
E.J. Wollack. “High-electron-mobility-transistor gain stability and its design
implications for wide band millimeter wave receivers”. Review of Sci. Instrum.
66 (8), August 1995.
A HFET LNA
K-band Map Amplifier
Typical Hetrodyne Receiver
Frequency Conversion
Linearity
Intermodulation
Some GBT Receivers
K band
Q band
Ka Band
Receiver Testing
Digitial Continuum Receiver
Lband XX (2) and YY (4)
Ku Band
Refrigerator Modulation
Ka Receiver (Correlation)
Zpectrometer
Lab Spectrometer Waterfall Plot
MUSTANG Bolometer
Focal Plane Array Challenges
•
•
•
•
Data Transmission ( State of the Art)
Spectrum Analysis ( State of the Art)
Software Pipeline
Mechanical and Thermal Design.
– Packaging
– Weight
– Maintenance
– Cryogenics
Focal Plane Array Algorithm
•
•
•
•
Construct Science Case/Aims
System Analysis, Cost and Realizability
Revaluate Science Requirements → Compromise
Instrument Specifications.
– Polarization
– Number of Pixels
– Bandwidth
– Resolution
K band Focal Plane Array
• Science Driver → Map NH3
– Polarized without Rotation
• Seven Beams → Limited by IF system
• 1.8 GHz BW → Limited by IF system
• 800 MHz BW → Limited by Spectrometer
Focal Plane Coverage
1. Initial 7 elements above 68%
beam efficiency (illumination
and spillover)
2. Expandable to as many as
61 elements
3. beam efficiency of outermost
elements would drop to ~60%.
4. beam spacing = 3 HPBWs
simulated beam efficiency
vs. offset from center
3 HPBW
28"
= 13.36 mm
K Band f = 22 GHz
88.9 mm
.177 HPBW/mm
KBand Focal Plane Array
K Band Single Pixel
Feed
Thermal Transition
Phase Shifter
Isolators
OMT
Noise
Module
HEMT
Sliding
Transition
Seven Pixel
What’s next for the GBT?
•
•
•
•
A W band focal plane array
Science Case is strong and under development.
Surface is improving
Precision Telescope Control System program is
improving the servo system.
• Needs.
– Digital IF system
– Backend (CICADA)
– Funding (Collaborators)
References
• Jarosik, et al. “Design, Implementation and Testing of the MAP
Radiometers”, N. The Astrophysical Journal Supplement, 2003, 145
• E.J. Wollack. “High-electron-mobility-transistor gain stability and its
design implications for wide band millimeter wave receivers”.
Review of Sci. Instrum. 66 (8), August 1995.
• M. W. Pospieszalski, “Modeling of Noise Parameters of MESFET’s
and MODFET’s and Their Frequency and Temperature
Dependence.” IEEE Trans. MW Theory and Tech., Vol 37. No. 9
• Norrod and Srikanth, “A Summary of GBT Optics Design”. GBT
Memo 155.
• Wollack. “A Full Waveguide Band Orthomode Junction.” NRAO
EDIR 303.
•
•
https://safe.nrao.edu/wiki/bin/view/GB/Knowledge/GBTMemos
https://safe.nrao.edu/wiki/bin/view/Kbandfpa/WebHome
Thank you for you attention!
• Questions?