1. © EMSS Antennas, TDP AWG, LAX, 6-7/5/2009 The KAT-7 feed package 1

2. © EMSS Antennas, TDP AWG, LAX, 6-7/5/2009 EMSS ? 2 A group of companies, operating from Stellenbosch, SA Employee-owned, 100 bodies, T/O ~ $M6 CEM code FEKO: www.feko.infowww.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

3. © EMSS Antennas, TDP AWG, LAX, 6-7/5/2009 The KAT-7 reflector: Revisited 3 Design freeze late 2007 –D = 12m (project decision, based on SKA trends) –F/D = 0.38 (Calculated to suit typical WBFs, also allowing a classical horn feed as fall-back) –Prime focus: Four struts, (+), ~2/3 out, cross-section shaped to minimise spillover –Surface to be flame-sprayed Aluminium or mesh, 1.5mm RMS –Drives: Elevation over azimuth

4. © EMSS Antennas, TDP AWG, LAX, 6-7/5/2009 The KAT-7 SPF 4

5. © EMSS Antennas, TDP AWG, LAX, 6-7/5/2009 The KAT-7 horn: Design freeze early 2008 5 Design briefs –1200 – 1950MHz (48%) –Orthogonal linear polarisations –Optimise A e / (T spillover + X) Results –Choked wide-angle horn, Ø = 1m (oversized) –Irises (for impedance matching af f lower ) –Theoretical TE 11 mismatch: ≤ –33dB –Theoretical T spillover : 5  2K –Theoretical illumination efficiency: 70  65%

6. © EMSS Antennas, TDP AWG, LAX, 6-7/5/2009 The KAT-7 horn: Theoretical results 6

7. © EMSS Antennas, TDP AWG, LAX, 6-7/5/2009 Theoretical A e / T sys (no blockage) 7

8. © EMSS Antennas, TDP AWG, LAX, 6-7/5/2009 The KAT-7 prototype horn 8

9. © EMSS Antennas, TDP AWG, LAX, 6-7/5/2009 The KAT-7 OMT 9 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

10. © EMSS Antennas, TDP AWG, LAX, 6-7/5/2009 The KAT-7 OMT size 10 Size does matter… –Final device quite small –0.2λ 3 –Thus small cryostat a real possibility –Theoretical performance very promising –(Typical quadridge structures = 3 – 6 λ 3 )

11. © EMSS Antennas, TDP AWG, LAX, 6-7/5/2009 The KAT-7 OMT 11

12. © EMSS Antennas, TDP AWG, LAX, 6-7/5/2009 The Kat-7 horn: Pattern measurements 12 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

13. © EMSS Antennas, TDP AWG, LAX, 6-7/5/2009 The Kat-7 horn: Pattern measurements 13

14. © EMSS Antennas, TDP AWG, LAX, 6-7/5/2009 The KAT-7 horn + OMT: Port properties 14

15. © EMSS Antennas, TDP AWG, LAX, 6-7/5/2009 The KAT-7 horn + OMT: Port properties 15 Loss? –Crude method: Short waveguide, divide insertion loss by two –Looks like 0.1+  dB –I.e., ~8K at ambient, and ~2K at 77K physical –Since verified by two OMTs back to back, transmission –0.2dB, confirming 0.1dB loss

16. © EMSS Antennas, TDP AWG, LAX, 6-7/5/2009 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. © EMSS Antennas, TDP AWG, LAX, 6-7/5/2009 The KAT-7 cryostat 17

18. © EMSS Antennas, TDP AWG, LAX, 6-7/5/2009 Conclusions 18 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.