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

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

4. Performance Limitations Surface (Ruze λ/16) – ξ = 50% – 300 µmeters → 63 Ghz Atmosphere e -t t = optical depth Spill Over T s Pointing Receiver Noise Temperature (Amplifier) T R

5. 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

6. Gregorian Subreflector

7. Prime Focus Feed Cross Dipole 290-395 MHz

8. 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

9. Optimizing G/T

10. Gregorian Feeds 140’ & 300’ Hybrid mode prime focus S, Ku (2x), L

11. 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

12. Prime Focus Receivers ReceiverFrequencyT rec T sys Feed PF1.1 0.290 - 0.395 1246 K X Dipole PF1.2 0.385 - 0.520 2243 K X Dipole PF1.3 0.510 - 0.690 1222 K X Dipole PF1.4 0.680 - 0.920 2129 K Linear Taper PF2 0.910 - 1.230 1017 K Linear Taper

13. Gregorian Receivers Frequency Band Wave Guide Band Temperature [GHz] [GHz] [º K] T rec T sys 1-2 L OMT (Septum) 620 2-3 S OMT (Septum) 8-1222 4-6 C OMT (Septum) 518 8-10 X OMT (Septum) 1327 12-15 Ku 12.4 -18.0 1430 18-25 K 18.0 - 26.5 2130-40 22-26 K 18.0 - 26.5 2130-40 26-40 Ka 26.5 - 40.0 2035-45 40-52 Q 33 - 50.0 40-7067-134 80-100 W 75 to 110 ~ 3 10^-16 W/√Hz

14. Receiver Room Turret

15. Receiver Room Inside

16. 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

17. Linear Polarization Orthomode Transducer

18. Circular Polarization

19. A Variety of OMTs

20. K band OMT

21. Equivalent Noise

22. Amplifier Equivalent Noise

23. Amplifier Cascade

24. Input Losses

25. HFET Noise Temperature

26. Radiometer

27. Correlation Radiometer (Ka/WMAP)

28. 1/f Amplifier Noise

29. MUSTANG 1/f Noise

30. HEMT 1/f Chop Rates Amplifier (band) ν o [GHz] Δ ν rf [GHz] f chop ( ε =.1 ) [Hz] Δ ν rf ( ε =.1, f = 5 Hz ) [GHz] L1.50.50.83 C4.0122 X10372 Ka3010800.6 Q45153750.2 W903015000.1 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.

31. A HFET LNA

32. K-band Map Amplifier

33. Typical Hetrodyne Receiver

34. Frequency Conversion

35. Linearity

36. Intermodulation

37. Some GBT Receivers K bandQ band

38. Ka Band

39. Receiver Testing Digitial Continuum Receiver Lband XX (2) and YY (4)

40. Ku Band Refrigerator Modulation

41. Ka Receiver (Correlation) Zpectrometer

42. Lab Spectrometer Waterfall Plot

44. MUSTANG Bolometer

45. 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

46. 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

47. K band Focal Plane Array Science Driver → Map NH 3 –Polarized without Rotation Seven Beams → Limited by IF system 1.8 GHz BW → Limited by IF system 800 MHz BW → Limited by Spectrometer

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

50. KBand Focal Plane Array

51. K Band Single Pixel Phase Shifter Thermal Transition OMT FeedNoise Module HEMT Isolators Sliding Transition

52. Seven Pixel

53. 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)

54. 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

55. Thank you for you attention! Questions ?