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Multi-Pixel Optics of SMA

Multi-Pixel Optics of SMA. Yun- Chih Chou, Chao- Te Li, Ming-Tang Chen Institute of Astronomy and Astrophysics, Academia Sinica. Outline. Current Status of SMA SMA Optics and Multi-Pixel Schemes Solution 1 Solution 2 Solution 3 Conclusion and Future Task. Current Status of SMA.

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Multi-Pixel Optics of SMA

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  1. Multi-Pixel Optics of SMA Yun-Chih Chou, Chao-Te Li, Ming-Tang Chen Institute of Astronomy and Astrophysics, Academia Sinica The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  2. Outline Current Status of SMA SMA Optics and Multi-Pixel Schemes Solution 1 Solution 2 Solution 3 Conclusion and Future Task The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  3. Current Status of SMA The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  4. SMA: Submillimeter Array • Antenna number: 8 • Antenna diameter: 6m • Full operation since 2005. • Location: Mauna Kea, Hawaii (4,045m) • Current operation frequencies: 176-256GHz, 250-350GHz, 330-430GHz. • Dual polarization observation: 345GHz • Field Of View: 14-70 arcsec Introduction of SMA The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  5. Receiver: Wide IF upgrade of 200GHz from 4-8GHz to 4-12GHz. • All 8 antennas have wide IF 200GHz receivers now. • Wide IF upgrade of 300GHz from 4-8GHz to 4-12GHz followed up, and two receivers have been installed. Receiver Update The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  6. SMA Optics and Multi-Pixel Schemes The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  7. Design purpose: Simple frequency-independent optics. • Design techniques: Fresnel imaging techniques, multi-mode Gaussian beam methods. • Frequency-independent illumination on secondary reflector: All bands have common “virtual feed” behind receiver lens. Original SMA Optics The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  8. Beam waveguide: M3 to M6 after Cassegrain reflectors. Ellipsoidal mirrors are M4 and M5. • Incidence angle of M4 and M5 is eliminated to reduce coupling loss on M5 (25 deg). • Advantage: Small coupling loss(M5 0.15% at 400GHz) and cross-polarization(-38dB at 3dB beam). Fresnel Imaging technique SMA Relay Optics The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  9. Wire grid: Added to split RF signals into high and low bands for dual observation (345GHz dual-polarization observation). • LO: Injection before receiver. • Receiver : Scalar horn and lens. • Feed Max gain: Max gain is reached when Bessel field of corrugated feedhorn is 10dB on aperture edge. Optics after RO The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  10. Advantage: Increase FOV and mapping speed. • Max FOV w/o cryostat window limit: • Observation frequency: 345 GHz, key frequency. Purpose of Adopting Multi-feed Arrays The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  11. Array element: 7 (hexagonal). Design goal: • Feature frequency: 345 GHz • Least modification in current optics. • Aperture Plane Array or Focal Plane Array. • Good performance: High beam efficiency, small spillover etc. Multi-pixel Arrays Scheme The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  12. Simple optics of SMA 300 band receiver was built in GRASP10. • Simulation method: Gaussian beam propagation and Physical Optics (PO) calculation. SMA Optics in GRASP10 The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  13. Beam efficiency: 81%, integrated to 10dB below peak. • Cross-polarization efficiency: 0.006% Fig. Copolar and Cross-polar El-Az Grid. Original Optics Result The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  14. Solution 1 The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  15. Optics: RO unchanged. • Smaller lens due to aperture limit: Diameter reduced from 70mm to 25mm, so all beams are less truncated at cryostat window (diameter 76mm). • Lens radius 12.5mm corresponds to 0.9ω (Gaussian beam radius). • Feed spacing: 25mm. Optics of Solution 1 The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  16. Lens truncation reduced beam efficiency greatly. Fig. Far-field cut of off-axis beam Fig. Solution 1 far-field beam grid of 3dB and 6dB. Simulation result The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  17. Solution 2 The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  18. Purpose: Reduce beam radius at lens position to eliminate lens truncation. • New RO, Feed and lens: Ellipsoidal mirror M5 is changed to produce more concentrated Gaussian beams. • Lens radius: 12.5mm, 1.25ω. • Feed spacing: 25mm. Optics of Solution 2 The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  19. Design method: Fresnel imaging techniques. • New parameter design goal: Similar value to original parameters. Table1. M5 parameters Table2. Feed and lens parameters Parameters of Sol. 2 The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  20. Sensitive Feed offset. • Severe spillover at secondary mirror. • In need of new RO design. Fig. Off-axis feed 25mm away from propagation axis. Simulation Result The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  21. Solution 3 The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  22. - Optics: RemoveRO. Original 300GHz lens and feed configuration. - Min. feed spacing : 2.44 * f# * λ = 29.7 mm. Optics of Solution 3 The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  23. Off-axis results have similar beam efficiency as on-axis. • This is the best solution of all solutions. Fig. On and off axis Copolar El –Az grid. Simulation Result The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  24. Conclusion and Future Task The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  25. Three solutions of 7-pixel feed arrays of SMA have been designed. Solutions Summary The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

  26. A new FPA solution with simple RO and largest FOV will be proposed. • Possible LO scheme: Change LO injection to waveguide coupling after feedhorn. Fig. All off-axis Gaussian beams distribution on main dish. Future Task The 13th Workshop on Submillimeter-Wave Receiver Technologies in Eastern Asia, Nanjing

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