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

2 OUTLINE OF TALK 1.Feed – Measured Results 2.Array Performance 3.Efficiency Comparison 4.Phase Shifter – Measured Results 5.OMJ – Measured Results

3 KFPA FEED Frequency GHz Feed taper -13 dB Compact/Profile taper horn Ring-loaded corrugations Aperture ID = 2.93”* (5.5λ 22 ) OD = 3.4” Length = 6.658” Pitch = 0.082” (λ 18 /8) Vane = 0.026” Depth = 0.13” (0.28λ 26.5 ) 69 corrugations Θ i = 8º ; Θ max = 17º *ID of linear taper horn=5.55”

4 Measured Patterns & Taper Freq. (GHz) H-pln (dB) E-pln (dB) Avg

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

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

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

11 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) FEED OFFSET & APERTURE EFFICIENCY -2%; measured -5% at 8.4”offset

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

13 Beam width & Beam spacing Freq. (GHz) HPBWBeam Spacing (HPBW) 1840” ” ” ”3.2 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 Freq. (GHz) Linear taperProfile1515ή apl- ή app ή apl (%) Edgetaper (dB) ή apl Edge taper (dB) ή app 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 Freq. (GHz) Linear taperProfileή apl- ή app ή apl (%) Edgetaper (dB) ή apl Edge taper (dB) ή app KFPA FEED Vs. 24 GHz FEED Telescope beam patterns, Efficiency

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

19 MEASURED RETURN LOSS

20 MEASURED INSERTION LOSS

21 MEASURED DIFFERENTIAL PHASE

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

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

LEADED BRASS Vs T6 ALUMINUM Property353 Leaded Brass6061-T6 Aluminum Composition (%) Cu 62, Pb 1.8, Zn 36.2 Al 97.92, Si 0.6, Mn 0.28, Mg 1.0, Cr 0.2 Density (lb/in 3 ) Thermal conductivity (BTU/ft. h.°F) Coeff. of thermal expansion (ppm/°C) Electrical Resistivity (μΩ.cm)

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

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

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” Feed: ID=4.54 OD=4.85 L=8.14 pc=5.9

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

30 Aperture Efficiency & System Temperature 3.4 “ OD Feed2.8” OD Feed Freq (GHz) Ap.Eff.System Temp (K) G/T (K/Jy) Freq (GHz) Ap.EffSystem Temp (K) G/T (K/Jy) Tspill