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Transcript of Centimeter Receiver Design Considerations with a look to the future Steven White National Radio...
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, KDesign Parameters: Length (Bandwidth), Aperture (Taper, Efficiency)
GBTα= 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
140’ & 300’ Hybrid mode prime focus
KFPA Feed
W band feed
140’ Prime Focus and Cassegrain Feed
S, Ku (2x), L
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 Frequency Trec Tsys Feed
• PF1.1 0.290 - 0.395 12 46 K X Dipole
• PF1.2 0.385 - 0.520 22 43 K X Dipole
• PF1.3 0.510 - 0.690 12 22 K X Dipole• PF1.4 0.680 - 0.920 21 29 K Linear Taper
• PF2 0.910 - 1.230 10 17 K Linear Taper
Gregorian ReceiversFrequency Band Wave Guide Band Temperature [GHz] [GHz] [º K]
Trec Tsys
• 1-2 L OMT (Septum) 6 20 • 2-3 S OMT (Septum) 8-12 22 • 4-6 C OMT (Septum) 5 18 • 8-10 X OMT (Septum) 13 27 • 12-15 Ku 12.4 -18.0 14 30 • 18-25 K 18.0 - 26.5 21 30-40 • 22-26 K 18.0 - 26.5 21 30-40 • 26-40 Ka 26.5 - 40.0 20 35-45 • 40-52 Q 33 - 50.0 40-70 67-134 • 80-100 W 75 to 110 ~ 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 RatesAmplifier
(band)
νo
[GHz]
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 TestingDigitial 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
simulated beam efficiencyvs. offset from center
1. Initial 7 elements above 68%beam efficiency (illuminationand spillover)
2. Expandable to as many as61 elements
3. beam efficiency of outermostelements would drop to ~60%.
4. beam spacing = 3 HPBWs
3 HPBW
K Band f = 22 GHz
28"
.177 HPBW/mm
= 13.36 mm
88.9 mm
KBand Focal Plane Array
K Band Single Pixel
Phase Shifter
Thermal Transition
OMT
Feed
Noise Module
HEMT
Isolators
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?