1. REU-Summer Student Seminars 14-June-2011 Signal Processing Instrumentation (RF / Analog) Ganesan Rajagopalan Electronics Department Arecibo Observatory

2. REU-Summer Student Seminars 14-June-2011 Talk outline Concept of Polarization & the need for dual polarization receivers Concept of Noise Figure / Noise temperature Basic Receiver architecture Dynamic range considerations Concept of System Temperature Super heterodyne down converter Techniques of receiver calibration (hot/cold loads, cal injection) Cryogenic Receiver Front-end design & construction Array receivers & telescopes in the near future FOV study using BYU Phased Array Feed

3. REU-Summer Student Seminars 14-June-2011 Nature of Radio emission Radio Sources –Thermal emission –Non-thermal synchrotron emission –Spectral line emission including Masers (partially polarized) –Pulsars Extremely weak, noise like signals Power collected=S Ae B S =Source flex density (watts/m^2/Hz) Ae=Telescope effective area (m^2) B=Bandwidth (Hz)

4. REU-Summer Student Seminars 14-June-2011 Arecibo’s Receivers & Transmitters enable really unique Science Aeronomy –Incoherent RADAR scatter studies of the ionosphere using 2 MW Pulsed RADAR & receivers at 430 MHz & 48 MHz. Planetary Astronomy – Imaging of Planets, Moons, Asteroids, Comets etc. using 1 MW CW Radar & receiver at 2380 MHz. Radio Astronomy –Galactic, Extra-galactic astronomy using ultra-sensitive receivers from ~ 300 MHz - 10 GHz for & Surveys using the multi-beam ALFA receiver. Plans for a ~100 element Phased Array Feed.

5. REU-Summer Student Seminars 14-June-2011 Radio Astronomical requirements High sensitivity, wide frequency coverage, data acquisition with very high spectral, spatial and time resolution. Remember, our receivers have to detect signals that are several orders of magnitude weaker than typical signals from: –cell phone towers –local FM station –nearby TV station –DirecTV geo-stationary satellite –NASA Spacecraft in the solar system RFI –Radio Freq Interference from nearby radars, cell towers cause serious issues

6. REU-Summer Student Seminars 14-June-2011 RADIO ASTRONOMY RECEIVER SYSTEM DanaPhil / Luis

7. REU-Summer Student Seminars 14-June-2011 Front-end of the Receiver Antenna Feed horn / dipole Polarizer & Low Noise Amplifier

8. REU-Summer Student Seminars 14-June-2011 DUAL-POLARIZATION ANTENNA (EQUIVALENT TO TWO ANTENNAS)

9. REU-Summer Student Seminars 14-June-2011 DUAL POLARIZATION RECEIVER

10. REU-Summer Student Seminars 14-June-2011 SINGLE AND DUAL-MODE TRANSMISSION LINES

11. REU-Summer Student Seminars 14-June-2011 CSIRO POLARIZATION SEPARATORS

12. REU-Summer Student Seminars 14-June-2011 Low Noise Amplifier Equivalent Noise Temperature Thermal and shot noise in transistors Dependance on physical temperature Cryogenic cooling improves sensitivity

13. REU-Summer Student Seminars 14-June-2011 Receiver is only as good as the very first amplifier in the chain Treceiver is mostly determined by the noise added by the first amplifier in the chain Noise added consists of thermal noise (coupled from the resistances in the device) & shot noise (from the quantized and random nature of current flow) –additionally inter-valley scattering, 1/f noise Both thermal & shot-noise contributions go down with temperature. So, we cool the front-end of our receivers to ~ 15 K Cooling the front-end to ~15K is achieved by a form of adiabatic expansion using 99.999% pure Helium in a closed cycle compressor system.

14. REU-Summer Student Seminars 14-June-2011 WHITE NOISE PRODUCED BY RESISTORS k=1.38 E-23 Watts/deg/Hz

15. REU-Summer Student Seminars 14-June-2011

16. REU-Summer Student Seminars 14-June-2011 NOISE ANALYSIS FOR CASCADED AMPLIFIERS

17. REU-Summer Student Seminars 14-June-2011 Berkshire Technologies, Inc.

18. REU-Summer Student Seminars 14-June-2011 Sky Contribution (includes the cosmic microwave background)

19. REU-Summer Student Seminars 14-June-2011 Receiver Characterization Receiver, Sky, Antenna & System temperatures T receiver, mainly from the first stage amplifier –measured by hot / cold “Y” factor method –room temp /liquid nitrogen /sky as reference absorbers T sky = T atmosphere + T background + ( T source ) T antenna = T sky + T spillover T system = T antenna + T receiver

20. REU-Summer Student Seminars 14-June-2011 Minimum detectable signal From statistics, we know the error on a measurement goes down as the square root of the number of independent samples. In a radio receiver with bandwidth “B” Hz, we get (B *  ) independent samples in an integration time of “  ” sec.

21. REU-Summer Student Seminars 14-June-2011 Minimum detectable signal

22. REU-Summer Student Seminars 14-June-2011 A simple receiver diagram Power received at the antenna P =k T a B K=Boltzman constant (joules/Hz/kelvin) T a =Antenna Temp. (kelvin) B=Bandwidth (Hz) Dual Polarization Rx. S Ae = k T Increase in T due to the source is usually a fraction of the total system noise, for most sources. So, several integrations over time is needed.

23. REU-Summer Student Seminars 14-June-2011 Typical Arecibo Receiver signal path Feed-horn at the focal plane Polarizer (linear or circular pol splitters) Noise injection Coupler Low Noise Amplifier Filter (bandpass) Post-Amplifier Down-converter / Frequency Translator Fiber-optic transmitter - receiver More Down-converter / Frequency Translator Sampler Spectrometers / Total power recorders Front-end/ RF IF/LO Digital Back-ends

24. REU-Summer Student Seminars 14-June-2011 Aerial view of the telescope 900 ton suspended platform held to within mm accuracy by laser ranging

25. REU-Summer Student Seminars 14-June-2011 Telescope Optics

26. REU-Summer Student Seminars 14-June-2011 Shaped reflectors correct the spherical aberration & bring the focus to a point inside the dome

27. REU-Summer Student Seminars 14-June-2011 Receiver Front-end Design, Construction, Characterization & Operation Feed horn designed to illuminate the tertiary optimally, without picking up a lot of spill-over radiation Polarizer designed to isolate the two linear or left/right circular polarizations Low Noise Amplifier (LNA) designed to add the least possible amount of additional noise Dewar designed to cool the Polarizer, noise injection coupler & amplifiers Cryo compressors & Cryo pumps use 99.999% He in closed cycle refrigeration system

28. REU-Summer Student Seminars 14-June-2011 Feed horns on a rotating turret on the focal plane

29. REU-Summer Student Seminars 14-June-2011 Spill-over contribution adds to Tsys Feed horn design is usually optimized to get the best possible (G / T) Depending on Feed horn design, the added noise can be as high as 12 K for the dome receivers Treceiver contribution is < 10K for most of the cooled receivers ~ 8K from Sky+Atm, <12 K from spillover, < 10K from receiver adds up to system temp < 30 K

30. REU-Summer Student Seminars 14-June-2011 The front-end receivers and RF/IF signal processing

31. REU-Summer Student Seminars 14-June-2011 DUAL BEAM DUAL POL. 6-8 GHz RECEIVER FRONT-END Block Diagram of a single beam section

32. REU-Summer Student Seminars 14-June-2011 C-band high ( 6- 8 GHz) construction Caltech/JPL InP LNA ~ 4 K Trx ~ 10 K Tsys ~ 25-30 K Polarizer, dewar designed by Cornell graduate student J. Pandian Dual beam, in future for continuum observations MMIC LNA 4-12 GHz

33. REU-Summer Student Seminars 14-June-2011 World record 2K Amplifiers uses Indium Phosphide transistors Now, inside our 4-6 GHz Rx : ~ 7 K Rx temperature.

34. REU-Summer Student Seminars 14-June-2011 Improved Tsys

35. REU-Summer Student Seminars 14-June-2011 Strong RFI from military radars, communication services, satellites and local sources Linearity is the most important requirement RFI causes receiver saturation and recovery problems & intermods. Switch-in Filters to cut down, if possible RFI mitigation RADAR blanking Flag off bad data in S/W Ref antenna & cross-correlation techniques RFI in 1.8 - 3.0 GHz band

36. REU-Summer Student Seminars 14-June-2011 Single Pixel vs. Array receivers Increase in mapping efficiency, ideal for large scale surveys. Gregorian optics limits the number of pixels Scanning losses increase as feed moves away from center. –ALFA outer beams’ gain is less by ~ 10 %

37. REU-Summer Student Seminars 14-June-2011 Arecibo L-band Feed Array Inside view of ALFA On it’s way up ! In place on the turret

38. REU-Summer Student Seminars 14-June-2011 The ALFA system The gain of the central beam is 11 K/Jy, the system temperature is about 25 K at 1400 MHz The gain of the outer beams is about 8 K/Jy The average beam size is 204 x 232 arc seconds. The six outer beams sit on an ellipse of 329 x 384 arc seconds.

39. REU-Summer Student Seminars 14-June-2011 ALFA SYSTEM LEVEL DIAGRAM

40. REU-Summer Student Seminars 14-June-2011 Wideband Single Pixel & Array Receivers German Cortes in Ithaca is working on octave bandwidth single pixel receivers several possible array receiver configurations

41. REU-Summer Student Seminars 14-June-2011 Arecibo’s FPA FOV Study -1.56 -1.84 -0.87 -0.86 -1.16 -10.04 -5.50 -6.01 -3.35 -4.25 -2.93 -4.31 -3.17 -5.51 -3.92 -7.72 -6.96 2. Non Uniform Plate Scale 3. Non Uniform Beam Power levels ~1700’’ ~1200’’ 5. Optimum Ne? 4. How much Incident Power a PAF could recover? 1. Caustics

42. REU-Summer Student Seminars 14-June-2011 The future is so exciting !

43. REU-Summer Student Seminars 14-June-2011 Thanx

44. REU-Summer Student Seminars 14-June-2011 Radio Receivers Advancing Technology leads to miniaturization & adds to functionality