Ultra-wideband Micro-strip Filter Design Based On Multi-mode Resonator

With the development of indoor wireless data access technology, ultra-widebandshort-range wireless communication has become a hot issue for scholars. Ultra-widebandfilter which is an essential part of UWB systems has been widely appreciated. So far, usingthe way of multi-mode resonator (MMR) to design ultra-wideband can basically meet thevarious requirements. This article is based on the MMR structure to meet the actual ofultra-wideband filter and dual-pass band pass filter with adjustable notch.Firstly, the basic theory of designing UWB filter is outlined, such as the filter type, thetechnical parameters, frequency transform and so on. For the traditional broadband filterdesigned, three different couplings are introduced, at the same time, the odd-even modemethod is presented.Secondly, stepped impedance resonator (SIR) and multi-mode resonator are describedabout the basic structure and the resonance condition. Then, a two-mode resonator filter isshowed based on SIR. Due to its relatively narrow bandwidth, utilizing MMR which cangenerate parasitic resonance in the low-frequency region of the pass band is to improve theperformance. The quantity of the resonance frequency in the pass band is changed from twoto three. The purpose of broadening the pass band is realized. Then, a dual-pass band filter isdesigned by using the parasitic resonance.Thirdly, the four-mode resonator filter which bases on EBG structure is designed. It canhas effectively suppress the higher harmonic because of having a relatively wide stop band.There are four resonant points in the pass band by loading open stub in the high impedanceline. These four resonant points are reasonable assigned in pass band to achieve the design ofthe ultra-wideband.Finally, the four-mode resonator filter is modified. A micro-strip line of interdigitalcoupling is folded up, it can curb the current. It is possible to realize adjustable notch byadjusting the length of the folding arm. Then, by comparing the parallel coupling with theinterdigital coupling, it is summarized that two different ways of coupling influence on theperformance of the same ultra-wideband filter.