Design Of Planar Multi-band/Multi-mode Microstrip Filter

In recent years, the filter, which is vital selected frequency component, plays an important role inwireless transceiver system. And the research will be focused on the performance of filter, such asminiaturization, low insertion loss, wide stop-band and out-band suppression. Stub-loaded and slit aregood methods to design filter, and filters which use these methods are simple structure and easymanufacture, so these two methods are widely used. In this thesis, several types of multi-band ormulti-mode planar microstrip filters are designed with these two methods.The first part introduces two tri-band passband filters which use Stub-loaded. Filters, which useasymmetric stub loaded, have three passband. Every passband has two transmission zeros that arelocated in two sides of passband, passband’s insertion loss is small, and attenuation between twopassbands is good. The length of stub and the location of stub loaded can change the performance ofthe passband, and two tri-band passband filters are fabricated to verify the theory. The high light ofthis part is that to design multi-band filter with asymmetric stub-loaded.The second part introduces several multi-mode passband filters that use symmetric stub loaded.Firstly, two different stubs loaded constitute a tri-mode bandpass filter, and the odd-even-modemethod is used to analyze. The even-mode frequency feven1can be adjusted by changing the radius ofcircular stub, the even-mode frequency feven2can be flexibly controlled by changing the length ofmicrostrip line, while the odd-mode frequency foddhardly changes. Secondly, in order to improvedifferent filter’s performance, two modified tri-mode bandpass filters are designed. Finally, byintroduced stubs to the original tri-mode bandpass filter, a new multi-mode bandpass filter was cameout. This filter has not only the improved passband performance but also a good upper stopband. It isthe improvements of this part that to design multi-mode passband filters with broad upper stop-bandthat use symmetric stub loaded.A multi-mode bandpass filter, which is composed of a square slit patch and a orthogonal feedstructure, is proposed in the last part. The study is focused on the relationship between the size of slitsand the resonance mode of passband, then detailed explanation of the multi-mode bandpass filter weregiven out. And this filter has good upper stopband and selection frequency performance. The highlight of this part is that to design multi-mode filter with several slits.