毫米波單平面梳形及交錯柵形濾波器之設計

Abstract

微波及毫米波濾波器中, 體積最小的就是梳形及交錯柵形濾波器. 以 往這類濾波器多用帶線(strip line)或微帶線(microstrip line)製作, 但是當頻率提升至毫米波頻段, 這類濾波器使用上述各種線製作變得十分 困難, 甚至根本不可行. 主要是因為寄生效應太過於強大, 例如包裹接地 線(wraparound)的電感, 傳輸線開路端的雜散電容等. 如果改用單平面線 則這些應會大大的降低, 使得這類濾波器工作到毫米波頻段變成可能. 但 是這類濾波器須使用多根耦合線, 這在同平面線時很難計算而且很容易激 發一些無法控制的模態, 所以直接套用從前的方法是不可行的。此論文擬 發展一種新的電路結構, 至多只使用到兩根同平面耦合線, 其結構十分類 似傳統的梳形及交錯柵形濾波器. 此方法避免了多根耦合線的問題, 但是 如何建立準確的等效線路模型則為主要目的. 希望能完成一套完整有效線 路分析及合成方法, 有足夠的準確性足堪使用到毫米波頻段; 同時也要製 作一些雛型線路以印證理論的正確性。 The combline and interdigital filter are two of the smallest size in those of microwave and millimeter wave filters. Usually, most of these filters are realized in strip line or microstrip line circuit type. However, when the frequency goes up to millimeter wave frequency range, these filter using above mentioned lines becomes very difficult or even impossible to realize. This is mainly due to the strong parasitic effects such as wraparound inductance, open end fringing capacitance, etc. All these parasitics were greatly reduced if uniplanar circuit was chosen. Without these parasitics to build a combline or interdigital filter in millimeter wave frequency range will be possible. These type of filters conventionally consist of multi- coupled lines will have big problem when using uniplanar line structure. Lack of accurate circuit model, and easy excite of unwanted modes make this uniplanar multi-compled line structure unusable. In this thesis, we plan to develop a novel circuit structure which uses at most two coupled uniplanar lines. The configuration is still similar to that of combline and interdigital filter. This method eliminates the multi-coupled lines problem. How to build an accurate equivalent circuit model is the main purpose of this thesis. It is believed that after finishing the thesis, an effective method to analyze and synthesize the circuit will be developed. Some prototype circuits will be built to verify the effectiveness of this method.