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EVLA Front-End CDR

EVLA Front-End CDR. Octave Bandwidth OMT Development in the 1-8 GHz Range. Frequency Ranges. L: 1- 2 GHz 2:1 (“Octave”) S: 2 – 4 GHz 2:1 (“Octave”) C: 4 – 8 GHz 2:1 (“Octave”) X: 8 – 12 GHz 1.5:1 Ku: 12 – 18 GHz 1.5:1 K: 18 – 26 GHz 1.44:1 Ka: 26 – 40 GHz 1.54:1

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EVLA Front-End CDR

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  1. EVLA Front-End CDR Octave Bandwidth OMT Development in the 1-8 GHz Range EVLA Front-End CDR – OMT Development April 24, 2006

  2. Frequency Ranges • L: 1- 2 GHz 2:1 (“Octave”) • S: 2 – 4 GHz 2:1 (“Octave”) • C: 4 – 8 GHz 2:1 (“Octave”) • X: 8 – 12 GHz 1.5:1 • Ku: 12 – 18 GHz 1.5:1 • K: 18 – 26 GHz 1.44:1 • Ka: 26 – 40 GHz 1.54:1 • Q: 40 – 50 GHz 1.25:1 EVLA Front-End CDR – OMT Development April 24, 2006

  3. Why Quad-Ridge? • Septum, Boifot types ~ 1.5:1 maximum • cf. Q-R horns 2-18 GHz • Low impedance structure EVLA Front-End CDR – OMT Development April 24, 2006

  4. “Good” Mode fco = 0.68 “Z” ~ 50 W fco = .91 “Z” ~ 500W fco = .74 EVLA Front-End CDR – OMT Development April 24, 2006

  5. “Bad Mode” fco = .69 fco = .88 fco = 1.28 EVLA Front-End CDR – OMT Development April 24, 2006

  6. fco vs. distance EVLA Front-End CDR – OMT Development April 24, 2006

  7. Quad-Ridge EVLA Front-End CDR – OMT Development April 24, 2006

  8. OMT Components thermal gap mode suppression Window Circular-to-Square Square-to-QR QR-to-coax EVLA Front-End CDR – OMT Development April 24, 2006

  9. Sliding Load EVLA Front-End CDR – OMT Development April 24, 2006

  10. EVLA Front-End CDR – OMT Development April 24, 2006

  11. Return Loss EVLA Front-End CDR – OMT Development April 24, 2006

  12. vs. ERA OMT EVLA Front-End CDR – OMT Development April 24, 2006

  13. Isolation EVLA Front-End CDR – OMT Development April 24, 2006

  14. 90-degree hybrid Hybrid In Coup. RCP Iso. Thru Nothing EVLA Front-End CDR – OMT Development April 24, 2006

  15. Mis-matched90-degree hybrid Hybrid In Coup. Less RCP Gr Gx Gy Gl Iso. Thru Some RCP EVLA Front-End CDR – OMT Development April 24, 2006

  16. Math EVLA Front-End CDR – OMT Development April 24, 2006

  17. Axial Ratio (Amplitudes;Voltages) EVLA Front-End CDR – OMT Development April 24, 2006

  18. For a< 1 dB • (With some assumptions) we can specify that the return losses of a pair of ports must sum to better than ~34 dB • This sort of tradeoff applies to any polarizer. • With perfect amplitude & phase, the sum would be ~25 dB. EVLA Front-End CDR – OMT Development April 24, 2006

  19. Next to do • Reduce mass of OMT. • Improve Cooling. • Better window material. • Investigate manufacturability. EVLA Front-End CDR – OMT Development April 24, 2006

  20. Conclusions • Prototypes have been built • Return loss is acceptable across band • Isolation is good across band • “Suck-out” suppression is effective EVLA Front-End CDR – OMT Development April 24, 2006

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