Design And Research Of Multi-band Filter And Switchable Triplexer Aimed Communication System Application

In recent years,with the rapid development in the field of communication industry,the communication system is developing toward the multi-service and highly integrated direction,therefore,the communication system for small,multi-band microwave device demand is more and more intense.Filter and multiplexer as the key front-end devices of RF microwave circuit,their performance directly affects the communication quality of the whole communication system.Therefore,the research of multi-band filter and multiplexer has very important research significance and research prospect.As the use of microstrip line design of microwave RF devices with low cost,miniaturization and ease of integration features,so,in the communication system,its application prospects are very wide.The main contents of this paper are as follows:(1)A highly selective dual-band filter based on the multi-stubs loaded step impedance resonator(SIR)is proposed.The odd-even mode theory is used to analyze the basic structure,and the frequency response characteristics are studied.The controllability of the modes is better,which can be controlled independently.By means of the appropriate bending of the microstrip to achieve the miniaturization of the circuit,while the short-circuit grounding hole produce the magnetic coupling and the low impedance part of SIR produce the electrical coupling.And two transmission zeros are introduced between the two passband because of mixed electromagnetic coupled.Meanwhile,extra two transmission zeros can be produced due to the introduction of source-load coupling.So,the dual-band filter has a high selectivity.And the center frequencies of two passband for this filter are 1.57GHZ(GPS)and 3.5GHz(WiMAX),respectively.The final measured results are in good agreement with the simulation results.(2)On the basis of the traditional two-order asymmetric SIR,an asymmetric ring loaded resonator(ASRLR)is proposed when the low-impedance part of SIR is replaced by the ring resonator.Based odd-even mode theory,the equivalent circuit model is analyzed theoretically,and the influence of each circuit parameter on the three resonant frequencies of the resonator is systematically studied.Finally,two tri-mode ASRLRs are coupled by means of pseudo-intersecting to form a tri-band filter.Several transmission zeros are created to improve the passband selectivity of the filter due to pseudo-interdigital coupling structure and skew-symmetrical 0° feeding structure.And the center frequencies of three passband for this filter are 1.57GHZ(GPS),3.5GHz(WiMAX)and 5.2GHz(WLAN),respectively.The final simulation results are in agreement with the experimental results.(3)Based on the previous theory of filter design,a six-pole high-temperature superconducting narrow-band triplexer based on a common net-type resonator is proposed,which has the characteristics of narrowband and high isolation.Then,on the basis of the previously designed high temperature superconducting triplexer,a PIN diode switch is introduced in each channel to achieve a high temperature superconducting switchplexer.And it can obtain eight working conditions to achieve the purpose of multi-channel switching by controlling the bias voltage to achieve the switch turning off and turning on.Compared with the filter devices fabricated on the conventional circuit board,the proposed switchplexer has characteristics of low loss and high isolation.