基于隐性多模耦合元件及电路互嵌法的微波多通带滤波器研究

As mobile communication and other wireless applications are developing, multi-band RF-frontends are becoming an important trend while multi-band filters are key conponents to costruct these systems. In the literature two kinds of solutions are presented. The first type combines several filters to realize multiple passbands while the second cascades several multi-mode resonators to achieve several passbands.The former has shortcoming of low circuit efficiency, thus resulting in big dimension, while the latter has difficulty in assigning bandwidths due to lacking of perfect multi-mode coupling schemes. This project firstly presents recessive multi-mode coupling element which is a cascading of connecting transmission line and two multi-mode capacitors.The multi-mode capacitors are incorporated into the circuit of multi-mode resonators, incuring the updation of resonating parameters.By adopting stepped-impedance stubs as multi-mode resonators we present synthesis methods for multi-passband filters and multi-stopband filters with up to 4 bands for each. Then a circuit-embedding technique is adopted that the passbands of a multi-passband filter are split by the stopbands of a multi-stopband filter, resulting in 5 to 8 passbands. The presented recessive multi-coupling scheme has no limit for the number of modes and the bandwidths can be freely assigned by synthesizing multi-mode resonators with required resonating parameters. The coupling networks are simplified, enabling the cascading of several resonators to construct multi-passband filters with higher order. The circuit-embedding technique gives compact dimension when doubling the number of passbands, and methods are given for controlling the bandwiths of the resulted passbands. High isolations between the resulted passbands are achieved because of the existance of transmission zeros. This project has practical importance for constructing multi-mode wireless systems.

随着无线通信和应用的发展，能够多频复用的射频前端成为重要发展趋势，而多通带滤波器是其中的关键器件。以往使用多滤波器组合或多模谐振器级联方案实现多通带，前者电路效率低,后者受限于耦合网络，难于控制各带宽。本项目针对多模谐振器方案提出隐性多模耦合元件，由连接传输线和多模电容级联而成，后者隐入多模谐振器电路，导致谐振参量的修正；基于阶梯阻抗短截线（直接加载和电容加载）分别综合出四频以下带宽可控的多通带和多阻带滤波器；通过带通/带阻滤波器电路互嵌将多个通带分割，获得五到八频多通带滤波器。隐性多模耦合元件不限模数，通过多模谐振器的谐振参量可自由调控各带宽，突破了以往耦合网络对通带数量的限制；也因为电路简单，方便了多个谐振器的级联，突破了滤波器的阶数限制；电路互嵌法以集约化方式实现了通带数量倍增，并可进一步调控各带宽。通带间因存在多个传输零点而产生高隔离。本项目对多制式无线系统的研制具有重要应用意义。

随着无线通信和应用的发展，能够多频复用的射频前端成为重要发展趋势。为构建多频多模射频前端，需要发展多种多频微波器件，其中多频滤波器是一种关键器件，而多频阻抗匹配网络是设计各种器件重要的基础元件。..本项目的主要工作是对微波多频滤波器的综合与设计作了研究，主要内容为：.1，研究了隐形多模耦合元件（多模J变换器）的基本电路和理论方法。其中包括了基于传输线的PI型网络和基于电容的PI型网络。.2，发展了多谐振器串联式的多模谐振器，结合电容PI型多模耦合元件，给出了中心频率和带宽完全可控的集总参数双频带通滤波器的综合方法。.3，发展了多短截线并联式的多模谐振器，结合传输线PI型多模耦合元件，给出了频率和带宽可控的分布参数带通滤波器的综合方法。并给出三频带通滤波器的设计。.4，基于双频带通和双频带阻滤波器互嵌和通带分裂的方法，实现两种四频带通滤波器，且频率和带宽可控。..与此同时，本项目拓展了多模J变换器的应用范围，在多频阻抗匹配网络和多频功率分配器方面作了研究，主要工作如下：.1，基于传输线Pi型多模J变换器和多频电纳元件，构建了针对任意复数负载的多频匹配网络的电路和综合方法。.2，基于集总参数Pi型多模J变换器和集总参数多频电纳元件，构建了针对任意复数负载的集总参数双频匹配网络的电路和综合方法，该方法可以进一步拓展用于三频以上阻抗匹配网络的设计。.3，基于经典的宽带匹配理论，使用低通-双频带通的频率变换方法，发展了针对RC、RL型负载的双频宽带的阻抗匹配网络。..本项目的重要结果和科学意义如下：.1，基于隐性多模J变换器的电路和概念，结合多模谐振器的参数提取方法，作多频滤波器的综合，可以简化滤波器的耦合电路，理论上可突破滤波器频带数量的限制。.2，隐性多模J变换器可以用于多频阻抗匹配网络的设计，该网络没有频段数量的限制，且使用了较少电路元件（传输线或集总元件）。这将会直接应用于多频功率放大器、多频天线的设计，具有重要的应用价值。.3，使用多频带通和多频带阻滤波器互嵌的电路结构，在不增加电路面积和体积的情况下，实现了通带数量的倍增。.4，结合宽带匹配理论和频率变换方法可拓展双频阻抗匹配网络的匹配带宽。