W頻段下低振幅不平衡與大於52%頻寬之相位正交耦合器設計

Abstract

波導管相位正交耦合器(waveguide quadrature hybrid)是天文接收機中常用的元件，在接收機中的作用為分離側帶(sideband separation)，將觀測頻率從單一側帶提升到雙側帶。執行側帶分離需要一對 RF 和 IF 相位正交耦合器，RF 耦合器的操作頻寬將會直接影響天文接收機的接收頻寬。在更大的頻寬下，可以讓單一接收機觀測更廣泛的天文頻譜，支持更多的科學觀測的進行。評估正交耦合器性能的另一個重點是其振幅不平衡(amplitude imbalance)和相位不平衡(phase imbalance)，這兩個參數的優劣會影響雙側帶接收機的鏡像拒絕比(image rejection ratio)表現。 在這篇論文中，將會介紹 W 頻段中三種不同的波導正交耦合器在設計、製造和測量上的紀錄。在第一和第二設計中，設計主軸為利用降低高度的波導管，能夠分別在兩個偶合器設計上達到操作頻率 74-116GHz 和 68-116GHz，超出了標準波導管的 75-110GHz 頻寬，其中兩個偶合器的振幅不平衡均<1.5 dB，偏離 90 度的相位誤差在 2 度以內。第三種設計引入了從主波導管(main-arm waveguide)的不連續性到耦合臂波導管(couple-arm waveguide)的寬度和高度的各種尺寸變數進行設計，以實現更低的振幅不平衡。在各種參數的最佳化調整後，第三種設計在 68-116GHz的頻寬底下能夠實現振幅不平衡<0.6 dB 以及 6 度以下的相位誤差。 論文正文將從背景需求和論文回顧開始，彙整三種耦合器的設計目標與流程、參數調整方法，最終介紹製造方式和測量結果。

Quadrature hybrid is a component commonly used in astronomical receiver for sideband separation, which double the observation frequency from single sideband to double sideband. A pair of RF and IF hybrids are required to perform sideband separation, and the operating bandwidth of the RF hybrid directly affect the receiving bandwidth of an astronomical receiver. Under larger bandwidth, more astronomical spectrum can be observed and the receiver can support more projects. Another concern of the quadrature hybrid is its amplitude imbalance and phase imbalance. Both parameters contribute to the image rejection ratio of double sideband receiver. In the article, three different waveguide quadrature hybrid couplers in W-band are investigated, design, fabricated and measured. In the first and second design, by utilizing the reduce height waveguide, the operation frequency is 74-116GHz and 68-116GHz, which is beyond the standard 75-110GHz pass band with < 1.5 dB amplitude imbalance and < 2 degrees phase error from 90 degree. The third design adapt various dimension variables from discontinuity of main-arm waveguide to the widths and heights of couplearms to achieve even lower amplitude imbalance. the amplitude imbalance of the third design is < 0.6dB with a trade in in phase error of <6 degrees for bandwidth 68-116GHz. The design flow and tuning method will conclude in the article, along with the manufacture and measure method.