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EM COMPONENTS UPDATE & PERFORMANCE RESULTS

This critical design review details the K-Band Focal Plane Array (KFPA) developed for the Green Bank Telescope (GBT), focusing on its performance across 18-26.5 GHz. Key metrics such as feed frequency, horn taper, and element configurations are explored, with results presented on aperture efficiency, beam patterns, and cross-polarization measurements. The findings also include optimal element orientation and spacing, alongside insertion and return loss data for the orthomode junction. This review serves as a foundational document for further developments in radio astronomy technology.

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EM COMPONENTS UPDATE & PERFORMANCE RESULTS

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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. 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

  3. Layout of Elements (61 feeds) Element spacing 3.45” 1+6+12+18+24

  4. 22 GHz; Telescope beams in Azimuth (asym.) planeHPBW = 34” Beam throw 27.4”/inch; 0.43HPBW/λ

  5. 22 GHz; Telescope beams in Elevation (symm.) planeHPBW = 34” Beam throw 27.4”/inch; 0.43HPBW/λ

  6. Feed Offset & Aperture Efficiency Circle #1 (3.4”rad): 7 feeds 62.9% min. Circle#2 (6.9”rad): 19 feeds 62.9% min. Circle#3 (10.4”rad): 37 feeds, 61.7% min. Circle#4 (13.8”rad): 61 feeds, 58.9% (az); 61.6% (el) Circle 18.0” : 91 feeds, 54.7% (az); 60.2% (el)

  7. Optimum orientation of Elements

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

  9. Measured Patterns & Taper

  10. Measured Cross-polarization in 45 deg. plane

  11. KFPA (Profile Horn) Feed Vs. 20 GHz (Linear Taper) Feed Measured feed patterns

  12. KFPA (Profile Horn) Feed Vs. 20 GHz (Linear Taper) Feed Telescope beam patterns, Efficiency

  13. KFPA (Profile Horn) Feed Vs. 24 GHz (Linear Taper) Feed Measured feed patterns

  14. KFPA (Profile Horn) Feed Vs. 24 GHz (Linear Taper) Feed Telescope beam patterns, Efficiency

  15. 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.

  16. MEASURED RETURN LOSS

  17. MEASURED INSERTION LOSS

  18. Measured Phase Difference

  19. ORTHO MODE JUNCTION 6061T6 Aluminum 353 Leaded brass 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

  20. 6061T6 ALUMINUM Vs. 353 LEADED BRASS

  21. Measured of S-parameters- Brass OMJ

  22. Measured of S-parameters- Al. OMJ Side arm Main arm

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