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Antenna, Feed, and LNA Integration S. Weinreb, May 7, 2009, LAX Antenna Working Group Meeting

Antenna, Feed, and LNA Integration S. Weinreb, May 7, 2009, LAX Antenna Working Group Meeting. Issues Feed Summary LNA Summary Differential LNA’s Feed LNA Interface Noise budget Summary and integration plan.

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Antenna, Feed, and LNA Integration S. Weinreb, May 7, 2009, LAX Antenna Working Group Meeting

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  1. Antenna, Feed, and LNA IntegrationS. Weinreb, May 7, 2009, LAXAntenna Working Group Meeting • Issues • Feed Summary • LNA Summary • Differential LNA’s • Feed LNA Interface • Noise budget • Summary and integration plan

  2. Losses – Increase in Tsys due to small losses in the interconnection. Difficult to keep these < 0.2 dB which adds 14K to Tsys. The addition can be as high at 30K when the considerations below are included. Differential LNA’s – Most wideband feeds have a differential (floating with respect to ground) output with impedance in the 100 to 270 ohm range. There is limited experience with the design, connections, and testing of these LNA’s. Input Reflections and Correlated Noise Out of Input – Especially important for phased-array feeds. Environmental – The LNA and feed must be protected against moisture, insects, rodents. lightning, temperature cycling and hail Mechanical – The feed connection points are small and difficult to mechanically support. A robust, easily manufactured design is needed. Feed/LNA Interconnect IssuesLow Frequencies (< 3 GHz) at 300K

  3. Losses – At higher frequencies the interconnections must be smaller (or they will radiate) and this increases the loss. However conductivity increases with cooling and a loss of 0.2 dB gives a tolerable ~4K noise at 70K physical temperature. Differential LNA’s – Same comments as for low frequency feeds.. Vacuum – Any cooling below dew point temperature requires sealing against condensation and vacuum insulation is usually required. This leads to a need for microwave windows and hermetic seals. Vacuum at 70K is more difficult than vacuum at 15K. Cooler – Compact, long life (>106 hours MTBF) coolers to 70K are available for ~$2,000 in quantity of Feed/LNA Interconnect IssuesHigh Frequencies (1.4 to 10 GHz) at < 70K

  4. Summary of Wideband Feeds From Bradley and Gawande, URSI Meeting, Boulder, Jan 2009

  5. Lindgren 3 to 12 GHz Quadridge Feed • Measured Tsys < 35K and efficiency > 40% on GAVRT 34m antenna. • Patterns improve with surrounding vacuum dewar • Have 50 ohm single-ended output so simple LNA’s can be used • Robust mechanical structure inexpensive to replicate/

  6. Noise vs Frequency of SiGe Transistor LNA at 3 Temperatures ST first stage, NXP 2nd stage, tested May, 2008 Typical gain 35 dB, typical bias 2V, 12mA

  7. Low-Cost SiGe 0.5 to 4 GHz Cryogenic LNA 7K noise at 17K with $.44 NXP transistor With STM transistor input stage noise is 2.5K at 17K, and 7K at 55K. SiGe transistors in 2mm plastic package on printed circuit board

  8. Noise Temperature vs Frequency at 300K, 195K, 105K, 77K, 60K, and 15K InP HEMT MMIC, WBA13, Tested at Caltech May, 2007

  9. Interface with Feed at 300K and LNA at 60K Output coax Input Twin-Lead Lines Active Balun (Differential) LNA for ATA

  10. Dual Differential LNA Module Can house either of 3 differential LNA chips on hand: ATA InP or 2 SiGe IBM Module and PCB’s in fabrication, April, 2009, expect test results by Aug, 2009 Transition from 270 ohm quadline to 135 ohm microstrips has been tested Dual 270 ohm resistors simulating feed impedance

  11. SKA Tsys Budget – Current and Expected 2011

  12. There are 5 candidates for wideband feeds currently under development. Pattern and noise measurements at a common facility are needed Cooled LNA’s for 0.5 to 3 GHz (< 7K noise at 60K) and 2 to 10 GHz (< 18K noise at 60K) are available. Room temperature LNA’s to meet the SKA Tsys < 35K requirement are difficult for 0.5 to 3 GHz and not feasible for > 3 GHz. Integration of feeds with LNA’s is in an initial phase with much progress expected in the next year. A US prototype antenna that can index to 3 different feed/LNA packages is recommended. Summary of Current Feed/LNA Status

  13. Integration Plan – May 2009 Feed pattern tests and optics optimization (by others) Test 3 differential LNA’s first in coaxial and then quadline fixture at 300K and 60K Dewar Construction and Cryogenic Test Test feed integrated with dewar at USC 2010 Noise and pattern test of integrated dewar, feed, and LNA 2011 System test on antenna, efficiency and Tsys

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