Research And Design Of Dual-band Microstrip Bandpass Filters Based On SIR And SLR

In recent years,wireless communication technology has shown a trend of diversified development,and various wireless communication protocols have been updated and emerged in endlessly.This requires that modern communication systems can be compatible with various communication protocols in different frequency bands.Higher requirements are put forward for signal selectivity of RF front-end circuits.Dual-band or even multi-band high-performance filters which are important devices for frequency screening have been widely studied and designed.This thesis mainly analyses two new types of resonators based on Stepped Impedance Resonator(SIR)and two new types of resonators based on Stub Loaded Resonator(SLR).Four new types of resonators are used to design dual-band microstrip bandpass filters with different characteristics.The main research contents are as follows:Firstly,based on the traditional SIR,the basic structures of open-circuited stub-loaded SIR and T-shape stub-loaded SIR are studied,and their resonance characteristics are analyzed by odd-even mode theory.Compared with the traditional SIR,the new types of resonator have higher design freedom.Two dual-band microstrip bandpass filters are designed by using these two new resonators,which adopt different coupled structures and feed modes.The transmission zeros are introduced by loading open stubs or using 0-degree feed structure in two new filters.The center frequency of the filter based on the open-circuited stub-loaded SIR is 2.45GHz/5.8GHz,and the filter insertion loss is 0.95dB/0.98 dB.Also,the center frequency of the filter based on the T-shape stub-loaded SIR is 2.45GHz/5.2GHz,and the insertion loss is 0.35dB/0.47 dB.These two dual-band bandpass filter can be applied in the WLAN(Wireless Local Area Network)band.Secondly,the asymmetric stub-loaded resonator is studied based on the symmetric SLR.Compared with the symmetric SLR,the stub-loaded position of the asymmetric SLR also affects the resonant frequency and bandwidth of the filter.The filter adopts a centrosymmetric electric coupling structure and introduces transmission zeros by using 0-degree feed structure.The dual-band bandpass filter with the center frequency of 3.5GHz/5.2GHz and insertion loss of 0.54dB/0.77 dB is designed,which can be applied in 5G(5th Generation)/WLAN band.Then,the various resonant operating modes of multi-stub loaded resonators are studied on the basis of single-stub loaded resonators.The idea of using four-mode resonator to design dual-band filter is put forward,and a dual-band bandpass filter with center frequency of 2.45GHz/3.5GHz and the insertion loss of 0.69dB/1.14 dB is designed by using this idea in this thesis,which can be used in WLAN/5G band.Finally,the above filters are fabricated and measured by a vector network analyzer.The theoretical analysis and simulation results are verified by the measured results.The four dual-band microstrip bandpass filters have certain practical application value,and provide some design ideas for the follow-up research.