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Centimeter Receiver Design Considerations with a look to the future

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)

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Centimeter Receiver Design Considerations with a look to the future

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  1. Centimeter Receiver Design Considerationswith a look to the future Steven White National Radio Astronomy Observatory Green Bank, WV

  2. Todd. Hunter, Fred. Schwab. GBT High-Frequency Efficiency Improvements, NRAO May 2009 Newsletter

  3. 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

  4. 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

  5. Gregorian Subreflector

  6. 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

  7. Optimizing G/T

  8. Prime Focus Feed Cross Dipole 290-395 MHz

  9. Gregorian Feeds S, Ku (2x), L W band feed KFPA Feed 140’ Prime Focus and Cassegrain Feed 140’ & 300’ Hybrid mode prime focus

  10. 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

  11. Prime Focus Receivers ReceiverFrequency 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

  12. Gregorian Receivers Frequency BandWave Guide BandTemperature [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

  13. Receiver Room Turret

  14. Receiver Room Inside

  15. 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

  16. Linear Polarization Orthomode Transducer

  17. Circular Polarization

  18. A Variety of OMTs

  19. K band OMT

  20. Equivalent Noise

  21. Amplifier Equivalent Noise

  22. Amplifier Cascade

  23. Input Losses

  24. HFET Noise Temperature

  25. Radiometer

  26. Correlation Radiometer (Ka/WMAP)

  27. 1/f Amplifier Noise

  28. MUSTANG 1/f Noise

  29. HEMT 1/f Chop Rates 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.

  30. A HFET LNA

  31. K-band Map Amplifier

  32. Typical Hetrodyne Receiver

  33. Frequency Conversion

  34. Linearity

  35. Intermodulation

  36. Some GBT Receivers K band Q band

  37. KaBand

  38. Receiver TestingDigitial Continuum ReceiverLband XX (2) and YY (4)

  39. Ku Band Refrigerator Modulation

  40. Ka Receiver (Correlation)Zpectrometer

  41. Lab Spectrometer Waterfall Plot

  42. Focal Plane Arrays

  43. MUSTANG Bolometer

  44. 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

  45. 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

  46. 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

  47. 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 Focal Plane Coverage simulated beam efficiency vs. offset from center

  48. KBand Focal Plane Array

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