Research On Microstrip Filters Based On Multimode Resonator And Their Application In Antenna Designs

Modern wireless communication systems,especially the mobile portable systems,have strict requirements on the compact circuit size and high-quality communication signal.Therefore,there is imperative demand on miniaturization and high performance for all types of microwave devices.Filters and antennas,whose size and performance directly determine the function of the whole communication system,are two essential parts of the communication system.This dissertation focuses on RF front-end devices with the properties of "miniaturization","high performance","integration" and "multiple functions".Research on microstrip filters based on multimode resonator and their application in antenna designs is carried out in this thesis.In details,a series of original work,including a bandpass filter,a dual-band bandpass filter,a UWB filter and the integration of filter and antenna,is achieved.The main contents of this dissertation are listed as follows:Firstly,according to the mechanism of "multi-mode",the multimode filters are divided into two categories: one is the multimode filters using the same-order modes and the other is the multimode filters based on multi-order modes.Correspondingly,the research background and the development process of the multimode filter are introduced according to the two categories,respectively.Besides,three common and useful technologies,including cavity mode method,transmission line theory and odd-even mode analysis,are briefly introduced,respectively.Then,several widely used coupling feed methods between the resonator and source are introduced.Secondly,a miniaturized microstrip triple-mode bandpass filter with Y-type central-loaded stub is presented.Compared with the commonly used perturbation and open-circuit loaded structures of ring resonators,the Y-type central-loaded stub can make good use of the internal spatial structure of the ring resonator to achieve the degenerate modes split and new mode excitation.Besides,a meander line structure is adopted to reduce filter physical size effectively.Finally,the proposed filter,which owns three transmission poles the passband and three transmission zeros(TZs)in the stopband,qualifies itself a good candidate for 2.4 GHz-2.4825 GHz of WLAN applications.Thirdly,as the further research of the operation mechanism of Y-type central-loaded stub structure,two dual-band bandpass filters are realized.Especially,the improved triple-mode dual-band bandpass filter could provide wide operating bandwidth,low insertion loss and excellent stop-band rejection.In detail,for each passband,the relative bandwidth is more than 10% and the minimum insertion loss is less than 1 dB.For the stopband,the out-of-band suppression is greater than 15 dB with seven TZs.The improved filter could cover the PCS(1.85GHz-1.99GHz)and WiMAX(3.3GHz-3.6GHz)frequency ranges well.Fourthly,an ultra-wideband(UWB)multimode filter,an UWB planar printed monopole antenna and their integration are investigated.Without increasing any original size of the UWB antenna,a novel integration technology of the multimode filter and UWB antenna are proposed.The filtering antenna owns the frequency selectivity characteristic and stable radiation pattern in the whole UWB band.It is worth pointing out that,the reported filtering antenna,as one of the important front-end equipment,has excellent properties,which includes "miniaturization","high performance","integration" and "multiple functions".