微波積體電路多模型濾波器設計及共平面波導之共振現象研究

Abstract

本文分為兩大部分. 第一部分提出在多模存在下如何設計出微小化濾 器. 利用平面製造技術及採用多重耦合懸浮式架構設計出的濾波器及雙工 器, 工作在K-頻段, 勿需微調即可表現出很好的濾波特性. 由於這種多重 耦合懸浮式架構具有多數模及非相鄰線間耦合的特性, 於是發展出一種新 的計算機輔助設計, 採用空間頻域法及微波多埠電路理論, 可同時考慮多 數模, 非相鄰線間耦合及蓋子的高度對濾波器的影響. 經由實際製作來做 一一的驗證. 實驗更證明因降低蓋子的高度, 減小了非相鄰線間的耦合 量, 使得濾波器有更好的阻帶特性. 所有量測結果與理論計算都非常吻 合.本文第二部分完整及系統化地探討背面有金屬之共平面波導的共振現 象. 一種全波分析法首先建立標準結果, 接著由一連串的實驗來確認理論 的正確, 所有的實驗電路在量測頻段內都發生共振現象. 在本文發展出的 全波分析法, 可以分析具有不連續介質的波導結構, 並可計算在多數模傳 播下的S-參數. 本文同時提出簡單的模型來實際了解與解釋電路的共振現 象. 由這種簡單的模型可以很準確的估算振盪頻率. 最後, 藉著全波分析 算出的金屬電流分佈, 可以很清楚地看出電路在共振或傳輸下的工作狀 態.結果發現電路在共振時, 絕大部分的能量集中在兩旁的金屬下, 而很 少能量能由中間的金屬來傳播. This thesis consists of two parts. The first part of the thesis proposes the design of miniaturized combline filter and diplexer in the situation of overmoded-wave propagation. The quasi-planar realizations of combline bandpass filter and diplexer using multiple coupled suspended substrate striplines (MCSSSs) have demonstrated good performance at K-band without any tuning. The N MCSSSs excite N zero-cutoff-frequency quasi- TEM modes. A new computer-aided filter design approach employing rigorous SDA (spectral-domain-approach) and 2N-port microwave circuit theory accounts for the effects of the N quasi-TEM modes, the couplings through non-adjacent MCSSSs, and cover height. Two 19.5-to-20.5 GHz MCSSSs combline filters with different cover heights are built and tested to compare their filter characteristics. The reduction in cover height decreases the amount of non-adjacent couplings through MCSSSs and results in better filter stopband performance. All the measured results for the combline filters and diplexer agree well with the theoretic calculations. The second part of the thesis presents a thorough and systematic investigation of resonant phenomena in conductor-backed coplanar waveguides (CBCPWs). A full-wave analysis is employed first to establish benchmark results and a series of measurements have been conducted to confirm the theoretical results. Two simple models are developed for physical understanding and interpretation of the resonant phenomena. Finally, by displaying the current distributions on the conductor strips in the through or resonant states of the test circuits, the MSL modes of resonances or the patch-type resonances can be clearly seen. When resonance occurs, the electromagnetic energy is confined or carried underneath the side planes and the signal energy can hardly propagate through the central signal line of the test circuit.