Research On Multi-band Microwave Filters

Filter is undoubtedly a hotspot in the communication field,which is the dispensable device.With the rapid development of technology,the customer demand for filters lead to miniaturization,multi-band,and high performance,which is becoming more mainstream.In this paper,several kinds of multi-band microwave filters are designed by using a variety of new resonators,analyzing each resonance theory with equivalent circuit,and the processing and testing are completed.The principal research contents are summarized as follows:1.A novel stepped-impedance resonator is proposed,using the odd-even-mode method analysis.(1)A dual-band filter designed by a novel stepped-impedance resonator,which is operating at 2.4GHz and 3.5 GHz,the 3d B frequency range is2.35GHz-2.5GHz and 3.45GHz-3.55 GHz,the insertion losses less than 0.7d B and0.9d B,the return losses better than 23 d B and 18 d B,and the fractional bandwidths of4.2% and 2.9%,respectively.(2)Another dual-band filter based on embedded resonators.The measured results shows that have 3d B frequency range is2.21GHz-2.55 GHz and 3.45GHz-3.7GHz,a central lower frequency at 2.35 GHz,which the insertion and the return losses were 0.6d B and 18 d B,respectively.A central higher frequency of 3.57 GHz with the insertion of 0.9d B and the return losses of 32 d B,respectively.2.A asymmetric T-type stub-loaded resonator is proposed,the theory of transmission lines is adopted to analyze,and design a dual-band and a tri-band filter.(1)A dual-band based on asymmetric T-type stub-loaded resonators.The measured results shows that the central lower frequency of 2.41 GHz which the insertion and return losses were 1.4d B and 30 d B,respectively.A central higher frequency at3.5GHz,with the insertion of 0.6d B and the return losses of 17 d B,respectively.(2)A tri-band filter designed by embedded resonators,which is operating at 2.48 GHz,3.58 GHz and 4.48 GHz,the 3d B frequency range is 2.36GHz-2.62 GHz,3.3GHz-3.76 GHz and 4.24GHz-4.64 GHz,the insertion losses less than 0.6d B,0.3d B and 1.01 d B,the return losses better than 15 d B,26 d B and 15 d B,and the fractionalbandwidths of 10.5%,12.8% and 8.9%,respectively.3.A tunable filter is presented based on open-loop resonators.By using the theory on dual-port networks parameters,combined with a 180° feed structure.And two varactor diodes are loaded at two ends of the opening of the resonators,designing a dual-band bandstop tunable filter with the center frequency can be continuously tuned from 1.8GHz-3.5GHz and 2.4GHz-5GHz.In the adjustable range,the insertion loss value is greater than 30 d B and 12 d B,the return loss value is less than 1.09 d B and 1.1d B,and the relative bandwidth is 6.3% and 6.8%.