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

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

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

22 GHz; Telescope beams in Azimuth (asym.) plane HPBW = 34” X” Throw (arcsec) (HPBW) 3.45 94 2.7 6.9 189 5.5 10.4 284 8.2 13.8 378 11.0 17.3 473 13.7 Beam throw 27.4”/inch; 0.43HPBW/λ

22 GHz; Telescope beams in Elevation (symm.) plane HPBW = 34” Throw (arcsec) (HPBW) 6 164 4.8 12 331 9.6 18 498 14.5 Beam throw 27.4”/inch; 0.43HPBW/λ

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)

Optimum orientation of Elements

Beam width & Beam spacing Freq. (GHz) HPBW Beam Spacing (HPBW) 18 40” 2.3 22 34” 2.7 24 31” 3.0 26.5 29” 3.2 Element spacing 3.45”; Beam spacing 94arcsec Beam throw 27.4 arcsec/”

Measured Patterns & Taper Freq. (GHz) H-pln (dB) E-pln 18 -11.7 -11.2 19 -12.6 -12.3 20 -13.2 -13.6 21 -13.7 -14.2 22 23 -13.5 -14.0 24 25 -13.0 -13.4 26 -14.3 26.5 -13.9 -14.7 Avg.

Measured Cross-polarization in 45 deg. plane

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

KFPA (Profile Horn) Feed Vs. 20 GHz (Linear Taper) Feed Telescope beam patterns, Efficiency Freq. (GHz) Linear taper Profile ήapl- ήapp ------------------ ήapl (%) Edgetaper (dB) Edge taper (dB) ήapp 18 -12.64 0.6995 -11.45 0.6965 0.43 20 -12.23 0.7284 -13.41 0.6560 9.94 22 -14.07 0.6888 -13.95 0.6189 10.15

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

KFPA (Profile Horn) Feed Vs. 24 GHz (Linear Taper) Feed Telescope beam patterns, Efficiency Freq. (GHz) Linear taper Profile ήapl- ήapp ------------------ ήapl (%) Edgetaper (dB) Edge taper (dB) ήapp 22 -12.10 0.6770 -13.95 0.6189 8.58 24 -12.58 0.6669 -13.48 0.6050 9.28 26.5 -12.46 0.6456 -14.32 0.5864 9.17

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.

MEASURED RETURN LOSS

MEASURED INSERTION LOSS

Measured Phase Difference

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

6061T6 ALUMINUM Vs. 353 LEADED BRASS

Measured of S-parameters- Brass OMJ

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