Research Of Microwave Filter Based On Multi-mode Resonator Structure

With the rapid development of wireless communication technology,multi-band bandpass filters and tunable filters which suit for various communication standards have gain more attention in the field of microwave circuits.Based on the multi-mode resonator,a small,high-performance microwave multi-band filter and tunable filter are designed.The main research work is as follows:1.Research of dual-band filter: A novel quad-mode resonator structure is proposed based on the tri-mode resonator,and the influence rules of the structural parameters on the four resonance frequencies are obtained by using the odd-even mode analysis methods.Through the resonator topology,the balance type dual-band filter coupled with the hook-type feed-line and the dual-band filter fed by the coplanar waveguide are designed respectively.The measured results show that the balance type filter is worked at 2.41 GHz and 5.29 GHz,which is suit for WLAN bands;the coplanar waveguide feed filter is worked at 1.9 GHz and 5.4 GHz,which is suit for the GSM and 5G-WIFI bands.Both dual-band filters have the characteristics of compact size and wide-band.2.Research of tri-band filter: A quad-mode resonator loaded with open-stub is theoretically analyzed.A novel six-mode resonator structure is proposed by loading stub on the quad-mode resonator.Feed structure is introduced to couple six resonance frequencies to form tri-band filter.The measured and simulated results are basically consistent,the center frequencies are loaded at 2 GHz?2.92 GHz and 3.73 GHz,and the out-of-band rejection is greater than 19 d B.It has the characteristics of miniaturization and multiple transmission zeros.3.Research of tunable filter: A wide-band filter is designed based on the quad-mode resonator,the structure is optimized by changing the length of stub.By loading varactor diode on the open-stub,a tunable wide-band filter is realized,the bandwidth,transmission zeros and center frequency can be tuned.Based on the balance type dual-band filter,a novel dual-band tunable filter is proposed,which has the characteristics of fixed low-passband and tunable high-band.The center frequency of the high-passband can be tuned from 5.3 GHz to 5.8 GHz.The design circuit has compact size,which has solved the problem of dual-band tunable filter size.