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Performance Analysis of K-Band Focal Plane Array Components

This presentation outlines the critical design review of a K-Band Focal Plane Array (KFPA) conducted on January 30-31, 2009. It covers the measured results of various components including feeds, array performance, efficiency comparisons, and phase shifters. Detailed discussions on the feed design (18-26.5 GHz), including compact/profile taper horn characteristics and measured patterns, are presented. The presentation also reports on aperture efficiency, beam patterns, and phase shifter performance, showcasing the validation of EM components and their effectiveness in applications related to cryogenically cooled receivers.

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Performance Analysis of K-Band Focal Plane Array Components

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  1. EM COMPONENTSUPDATE & PERFORMANCE RESULTS S. Srikanth Critical Design Review GBT K-Band Focal Plane Array January 30-31, 2009

  2. OUTLINE OF TALK • Feed – Measured Results • Array Performance • Efficiency Comparison • Phase Shifter – Measured Results • OMJ – Measured Results

  3. KFPA FEED Frequency 18-26.5 GHz Feed taper -13 dB Compact/Profile taper horn Ring-loaded corrugations Aperture ID = 2.93”* (5.5λ22) OD = 3.4” Length = 6.658” Pitch = 0.082” (λ18/8) Vane = 0.026” Depth = 0.13” (0.28λ26.5) 69 corrugations Θi = 8º ; Θmax = 17º *ID of linear taper horn=5.55”

  4. Measured Patterns & Taper

  5. 22 GHz; Theory & Measured E-plane H-plane

  6. Measured Cross-polarization in 45 deg. plane

  7. Measured Input Return Loss

  8. LAYOUT OF ELEMENTS (61 Feeds) Element spacing: Ring: 3.45” Az: 3.45” El: 5.98” No. of feeds in the rings 1+6+12+18+24

  9. 22 GHz; Telescope beams in Azimuth (asym.) planeHPBW = 34” * Theoretical feed patterns used Beam throw 27.4”/inch; 0.43HPBW/λ

  10. 22 GHz; Telescope beams in Elevation (symm.) planeHPBW = 34” * Theoretical feed patterns used Beam throw 27.4”/inch; 0.43HPBW/λ

  11. FEED OFFSET & APERTURE EFFICIENCY Ring #1 (3.4”rad): 62.9% Ring #2 (6.9”rad): 62.9% Ring #3 (10.4”rad): 61.7% min. Ring #4 (13.8”rad): 58.9% (az) -6.3%; 61.6% (el) -2% Circle 18.0” rad: 54.7% (az); 60.2% (el) -2%; measured -5% at 8.4”offset

  12. Initial Orientation of Elements Optimum Orientation of Elements Ring #1,2: 0%;#3: -2%;#4:-6.3% Ring #1,2: 0%;#3: <-2%;#4:-3.5%

  13. Beam width & Beam spacing Element spacing 3.45”; Beam spacing 94arcsec Beam throw 27.4 arcsec/”

  14. KFPA FEED Vs. 20 GHz FEED Measured patterns KFPA Feed – Profile Horn (-13.3,-13.5 dB) 20 GHz Feed – Linear Taper Horn (-12.8,-11.7 dB)

  15. KFPA FEED Vs. 20 GHz FEED Telescope beam patterns, Efficiency

  16. KFPA FEED Vs. 24 GHz FEED Measured patterns KFPA Feed – Profile Horn (-13.3,-13.7 dB) 24 GHz Feed – Linear Taper Horn (-13.1,-12.1 dB)

  17. KFPA FEED Vs. 24 GHz FEED Telescope beam patterns, Efficiency

  18. 18-26.5 GHz Phase Shifter 0.474 x 0.452; Length 4.84” S. Srikanth, “A Wide-Band Corrugated Rectangular Waveguide Phase Shifter for Cryogenically Cooled Receivers”, IEEE Microwave and Guided Wave Letters, Volume 7, pp. 150-152, June 1997.

  19. MEASURED RETURN LOSS

  20. MEASURED INSERTION LOSS

  21. MEASURED DIFFERENTIAL PHASE

  22. ORTHO MODE JUNCTION 353 Leaded brass; Weight 1 lb WR42 waveguide; 4.5” x 2.8” Septum 0.010” (Beryl. Cu) Pin 0.040” dia. (Beryl. Cu) E. Wollack, “A Full Waveguide Band Orthomode Junction”, EDIR No. 303, NRAO, May 16, 1996

  23. ORTHO MODE JUNCTION 6061-T6 Aluminum; Weight 0.33 lb

  24. 353 LEADED BRASS Vs.6061-T6 ALUMINUM

  25. Measured S-parameters- Brass OMJ Measured by R. Hayward, NRAO, Socorro, NM

  26. Measured S-parameters- Aluminum OMJ #1: 18 GHz; #2: 26.5 GHz;#3; 27.5 GHz Side arm Main arm Measured by R. Simon, NRAO, Green Bank, WV

  27. CONCLUSION All EM components have been validated. Feed: 3 nos. tested; 5 nearly finished Phase shifter: 2 good ones; 10 being electroformed OMJ: 1 no. of aluminum OMJ tested; 7 nos. Al. on order 2 nos. Brass- tested Circular-rectangular transition, 45 twist: 8 nos of each finished.

  28. Pc 3”-4.2” 22-26.5 Feed: ID=4.54 OD=4.85 L=8.14 pc=5.9

  29. Phase patterns & Phase centers PC at 22 GHz PC at 18 GHz PC at 26 GHz

  30. Aperture Efficiency & System Temperature Tspill

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