EM COMPONENTS UPDATE & PERFORMANCE RESULTS

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 3.45” 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 Circle #1 (3.4”rad): 62.9% min. Circle#2 (6.9”rad): 62.9% min. Circle#3 (10.4”rad): 61.7% min. Circle#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. Optimum orientation of Elements

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 (-13.5,-13.3 dB) 20 GHz Feed – Linear Taper Horn (-11.7,-12.8 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 (-13.7,-13.3 dB) 24 GHz Feed – Linear Taper Horn (-12.1,-13.1 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. 6061-T6 ALUMINUM Vs. 353 LEADED BRASS

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. Phase shifter: 2 good ones; 6 being electroformed OMJ: 3 nos. of aluminum OMJ Circular-rectangular transition, 45 twist: 10 nos of each being processed.

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