77-118 GHz寬頻墊片極化器

A 77-118 GHz Resonance-Free Septum Polarizer

陳彥麟

極化器 ； 毫米波 ； 電波天文觀測 ； 圓波導管 ； Polarizer ； Millimeter wave ； Radio astronomy Observation ； Circular Waveguid

國家奈米元件實驗室奈米通訊

24卷4期（2017 / 12 / 01）

16 - 21

繁體中文

現今毫米波/次毫米波(Millimeter/Sub-millimeter)的天文望遠鏡經常使用墊片極化器(Septum Polarizer)或是正交極化轉換器(Ortho-mode Transducer, OMT)來進行天文極化觀測。在此研究裡，W頻段墊片極化器的寬頻被提升到了42% (77-118 GHz)，不在有窄頻的缺點，高頻共振也不再出現。因墊片極化器適合觀測線型極化，所以配備墊片極化器的望遠鏡將會比配備OMT的望遠鏡更具優勢經。此極化器的Stokes I/Q Leakage在2%以內，Stokes Q/U Leakage在1%以內。我們也製作出G頻段(140-220 GHz)的墊片極化器則，說明其往高頻應用的潛力。

Polarization-capable, millimeter/sub-millimeter telescopes are normally equipped with either septum polarizers or ortho-mode transducers (OMT) to detect polarized radiation. Though the septum polarizer is limited to a significantly narrower bandwidth than the OMT, it possesses advantageous features unparalleled by the OMT when it comes to determining astronomical polarization measurements. Challenging the conventional bandwidth limit, we design an extremely wide-band circular waveguide septum polarizer, covering 42% bandwidth, from 77 GHz to 118 GHz, without any high-order resonance. The performance of this polarizer has been verified in between 75 GHz and 115 GHz. The Stokes parameters constructed from the measured data show that the leakages from I to Q are below ±2% and the Q/U mutual leakage below ±1%. This result removes the major weakness of the septum polarizer and opens up a new domain of astronomical instrumentation for polarization measurement. Despite this polarizer is designed to cover 77-118 GHz, it can be straightforwardly downsized to cover higher frequencies with minor change. The measurement result of a G-band (140-220 GHz) polarizer is also presented.