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The KAT-7 feed package

The KAT-7 feed package. 1. EMSS ?. A group of companies, operating from Stellenbosch, SA Employee-owned, 100 bodies, T/O ~ $M6 CEM code FEKO: www.feko.info EMSS Antennas (8 bodies) Contracted into MeerKAT project, cost-plus-material basis, shared risk

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The KAT-7 feed package

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  1. The KAT-7 feed package 1

  2. EMSS ? • A group of companies, operating from Stellenbosch, SA • Employee-owned, 100 bodies, T/O ~ $M6 • CEM code FEKO: www.feko.info • EMSS Antennas (8 bodies) • Contracted into MeerKAT project, cost-plus-material basis, shared risk • Self-representative on subsystem level • Develop and implement feed technology, act as custodians of EM issues 2

  3. The KAT-7 reflector: Revisited • Design freeze late 2007 • D = 12m (project decision, based onSKA trends) • F/D = 0.38 (Calculated to suit typicalWBFs, also allowing a classicalhorn feed as fall-back) • Prime focus: Four struts, (+),~2/3 out, cross-section shaped tominimise spillover • Surface to be flame-sprayedAluminium or mesh, 1.5mm RMS • Drives: Elevation over azimuth 3

  4. The KAT-7 SPF 4

  5. The KAT-7 horn: Design freeze early 2008 • Design briefs • 1200 – 1950MHz (48%) • Orthogonal linear polarisations • Optimise Ae / (Tspillover + X) • Results • Choked wide-angle horn, Ø = 1m (oversized) • Irises (for impedance matching af flower) • Theoretical TE11 mismatch: ≤ –33dB • Theoretical Tspillover: 5  2K • Theoretical illumination efficiency: 70  65% 5

  6. The KAT-7 horn: Theoretical results 6

  7. Theoretical Ae / Tsys (no blockage) 7

  8. The KAT-7 prototype horn 8

  9. The KAT-7 OMT • Design briefs (early 2008) • Smaller than typical bladed OMTs (to facilitatte small cryostat) • High-fidelity, no hybrid devices • Chosen candidate • Two crossed dipoles in shorted waveguide • Impedance-transforming feeder lines • Two Marchand baluns • Design method: Aggressive space mapping 9

  10. The KAT-7 OMT size • Size does matter… • Final device quite small • 0.2λ3 • Thus small cryostat areal possibility • Theoretical performancevery promising • (Typical quadridgestructures = 3 – 6 λ3) 10

  11. The KAT-7 OMT 11

  12. The Kat-7 horn: Pattern measurements • Pattern verification • 500m Ground-reflection far-field range • Principal planes and diagonal cuts made • Fed by prototype single-mode transducer • Found excllent agreement with CEM predictions 12

  13. The Kat-7 horn: Pattern measurements 13

  14. The KAT-7 horn + OMT: Port properties 14

  15. The KAT-7 horn + OMT: Port properties • Loss? • Crude method: Short waveguide, divide insertion loss by two • Looks like 0.1+ dB • I.e., ~8K at ambient,and ~2K at 77Kphysical • Since verified by twoOMTs back to back,transmission –0.2dB,confirming 0.1dB loss 15

  16. The KAT-7 cryostat • Design briefs • Small vessel, robust • Stirling-cycle cryo-cooler • Sunpower GT unit: 15W at 77K (neck at 30°C) • Cold fluid up from pedestal, for cooling the cooler • No mechanical vacuum maintenance • Ion pump, carbon traps, limited cryo-pumping at 77K • Host to LNAs and noise injection circuitry • Life support from pedestal below 16

  17. The KAT-7 cryostat 17

  18. Conclusions • Good horn performance from prime focus • Very good performance from small OMT • Getting there with a small robust cryostat • Full development will be captured in a project memo, towards end of 2009 • Thank you. 18

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