環形耦合器之廣義合成及其電路微小化之應用

Abstract

本論文的第一部分闡述環形耦合器的廣義合成，根據環形耦合器必須滿足的條件，使用傳輸線理論及奇偶模分析可推論得到所有的電路參數，由數學分析可得知：我們可以設計出無限多組電路。為了驗證本論文提出的理論，我們設計一個周長為0.97個波長(傳統環形耦合器周長為1.5個波長)的電路，它的面積只占傳統環形耦合器的41.82%. 某些廣義環形耦合器的頻寬模擬值也被提出並探討，頻寬與電路尺寸之間的關係也在此做深入的討論。 第二部分研究步階式阻抗對於電路微小化的影響。將環形耦合器的四段傳輸線等效代換成步階式阻抗，不但仍保持環形耦合器的特性，而且可縮短電路的周長。論文第一部份設計出的電路若使用此方法可以有效地縮小電路，如果此電路的中心頻率設計在1 GHz, 縮小後的電路面積只會占傳統耦合器的13.12%, 我們相信，在目前的開放文獻中，這個電路的面積是所有微帶線環形耦合器中最小的一個。 論文中包含兩組實作電路，它們的量測結果證實與模擬值吻合。

Generalized synthesis of the rat race ring coupler is developed with its four arms being allowed to have different characteristic impedances and electrical lengths. The transmission line theory incorporated with the even-odd analysis is used to formulate the conditions for solving the circuit parameters. The solution shows that a rat race ring with a normalized area of 41.82% or 0.97wavelength-circumference can be achieved. Based on the solutions, simulated bandwidths of the new ring hybrids are reported. Two experimental circuits are measured for validation check. One uses stepped-impedance sections to realize the four arms for further size reduction. This circuit occupies only 13.12% of that of a conventional hybrid ring at 1 GHz. It is believed that this implementation has the best size reduction for a microstrip ring hybrid in open literature. Measured scattering parameters show good agreement with the simulated results.