Design Of Multi-Band/Multi-Mode Microstrip Filter Based On Sir

In recent years, with the rapid development of wireless communication, the requirement ofcommunication system’ performance is rising higher and higher. The filter plays an important role inthe part of RF front-end. Small sizes and high performance of filtering characteristic cause more andmore attention. Stepped impedance resonator (SIR) as new structure composing filters which cansatisfy the demand of small size, good out-band suppression are widely used in designing filter.Several types of multi-band and multi-mode microstrip filter based on SIR with high performance aredesigned in this paper.Firstly, the dissertation introduces design parameters of filter, three types of transfer functions andfrequency transformations are introduced. Then, the common structures of SIR are given. Theresonance condition, spurious resonance frequency and equivalent circuit of SIR are analyzed. Theseare necessary theoretical guidance and technical support to design filter.In the second place, the compact dual-band bandpass filter wide stopband rejection is proposed.The spurious resonance frequency of SIR can be tuned by changing the impedance ratio. Theskew-symmetric (0-degree) feed structure and source-load coupling are also used. The filter has goodperformance of in-band and out-band. Meanwhile, because the inter-digital capacitor is introduces, itreduces the size of filter. The filter has better performance on miniaturization. Then, a triple-banddual-mode BPF using short-circuited stub-loaded SIR with an excellent mid-band rejection isdesigned. According tio the odd-even-mode method, the even-mode frequency can be flexiblycontrolled by changing the length of the short stub in central plane, whereas the odd-mode oneremains stationary. And by changing the impedance ratio of SIR, the first high spurious frequency canbe adjusted to the desired passband. Two sets of short-circuited stub-loaded SIR at diverse frequenciesto generate three passbands.The third aspect of the research lies in multi-mode filter designs. A triple-mode BPF using novelstub loaded UIR is firstly proposed. Also according to the odd-even-mode method, the even-modefrequencyf1evencan be flexibly controlled by changing the length of the short stub in central plane,and the even-mode frequencyf2evencan be adjusted by changing the length of closed microstrip line,while the odd-mode one remains stationary. Secondly, in order to provide sufficient degrees offreedom for achieving wide stopband rejection of filter, by using the source-load coupling structure, ahigh selectivity triple-mode BPF using novel stub loaded SIR is designed. The filter has wider stopband rejection and better selectivity. At last, a triple-mode BPF using circular impedance-steppedstub and two open stubs loaded SIR with wide stopband rejection is proposed. The even-modefrequencyf1evencan be flexibly controlled by changing the radius of the circular impedance-steppedstub in central plane, and the even-mode frequencyf2evencan be adjusted by changing the length oftwo open stubs. By using circular impedance-stepped stub, the filter has wide stopband rejection.