A Modular K-Band Focal Plane Array for the Green Bank Telescope Matt Morgan National Radio Astronomy Observatory 9/28/2007

Baseline Instrument Specifications SpecificationRequirement Frequency Band GHz (complete K-Band coverage) T RX (each beam, not including sky)< 25 K (75% of band) * < 36 K (entire band) Number of beams7 Polarizationdual, circular (axial ratio <= 1 dB) SIdeband (image) rejection> 30 dB Instantaneous RF Bandwidth1.8 GHz Mass< 100 kg Headroom> 30 dB (to 1 dB compression point) * Should in fact be equivalent to EVLA receiver noise temperatures.

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

Key Subsystems 1.Feedhorn Array 2.Cryogenic Dewar 3.Cooled Electronics 4.Integrated Downconverter Modules (IDM) 5.LO Distributions and M&C 6.IF Transmission System

Bandwidth Limitations Sub-AssemblyTotal Potential Bandwidthcomments cold-electronics (feed, OMT, LNA...) >8.5 GHzperformance degrades gracefully outside of GHz warm analog electronics 1.7 GHz (up to 8 dual- polarized beams limited by existing IF transmission system, requires multiplexing digital electronics800 MHz (4 beams) 50 MHz (8 beams) limited by existing spectrometer

Potential Upgrade Paths for IF Transmission System Methods for increasing IF tranmission bandwidth and number of channels:  install additional analog fibers  modulate additional colors on existing fibers  digitize at the antenna, and use commercial digital fiber links  preferred solution with greatest long-term potential  may also employ digital filtering/decimation or compression at the antenna Note that all of these would provide enhanced capability to all focal plane arrays, regardless of the frequency band. However, only the last one is likely to be able to handle the extreme data volumes produced by large-format "cameras" such as a W-Band array with a hundred or more elements.

Pixel Design

Pixel Performance Calculation Worksheet G sys = dB T sys = K (T sky = 75K) P out = dBm min. headroom = 35.2 dB

Program Schedule

Milestones  1/15/2008System design complete with Conceptual Design Review acceptance.  5/13/2008M&C hardware module with support software complete.  5/8/2008Single pixel construction complete.  8/8/2008Single pixel testing complete with Critical Design Review acceptance.  1/6/2009Multi-Pixel dewar assembly complete.  2/13/2009Observing support software complete.  6/9/2009Multi-pixel testing and construction complete.  11/3/2009System integration and lab testing complete.  2/8/2010Data analysis software complete.  4/6/2010Telescope testing complete.  11/8/2010Commissioning complete.

Cost Summary ItemLM BudgetTotal Cost Total Funded Labor$ 824k Total GB Operations Labor$ 0k$ 468k Total Parts Cost$ 190k Contingency$ 202k Total$1216k$1684k (detailed cost breakdown available if needed)

Open Issues  Exact frequency coverage of the front end. Is this optimal for the science? What are the technical options?  What are the desired polarization characteristics of the array? Is the choice of circular polarization for all feeds the best?  Noise injection: is there a need for various intensity cals?  Feed rotator: is it necessary? What should its specs be? (This needs to be considered in the contect of the performance of the off-axis feeds, which may not be symmetric around the central pixel).  Feed pattern: any better options than close-packed hexagon?  Continuum mapping capabilities: should this be any consideration? If so, what does it imply?  Operational issues: telescope scanning to fill in the coverage; subreflector nodding?

BACKUP SLIDES FOLLOW

Labor Estimates: Year 1 ItemMachinist [FTEs] Technician [FTEs] Astronomer [FTEs] Engineer [FTEs] Eng&Tech GB ops [FTEs] Compact Feedhorn Noise Calibration Module (NCM) Integrated Downconverter Module (IDM) LO Distribution M&C, biasing, PCB design and layout Mechanical design (overall receiver, cryostat) Parallactic Angle Rotator Project management Systems engineering Project scientist Software Development Total FTEs: Funded Total = $368k Total GB Ops = $302k

Labor Estimates: Year 2 ItemMachinist [FTEs] Technician [FTEs] Astronomer [FTEs] Engineer [FTEs] Eng&Tech GB ops [FTEs] NCM housing and assembly IDM housing and assembly Project management Systems engineering Receiver assembly and cabling Project scientist Software Development Total FTEs: Funded Total = $295k Total GB Ops = $133k

Labor Estimates: Year 3 ItemMachinist [FTEs] Technician [FTEs] Astronomer [FTEs] Engineer [FTEs] Eng&Tech GB ops [FTEs] Receiver Engineer Project scientist Software Development Total FTEs: Funded Total = $160k Total GB Ops = $ 34k

Parts Cost PartQty.Unit costExtended cost Feedhorns7 $ 2.0k$ 14.0k Phase shifters and transitions7 $ 7.0k$ 49.0k OMTs7 $ 2.0k$ 14.0k Isolators14 $ 0.5k$ 7.0k NCM parts14 $ 0.8k$ 11.2k LNAs14 $ 3.0k$ 42.0k IDM parts7 $ 2.9k$ 20.3k LODM&C parts1 $ 5.0k Refrigerator1 $ 8.0k Parallactic Angle Rotator1 $19.5k Funded Total = $190k