Study On High-performance And Miniaturized Microwave Filters And Multiplexers

The rapid advancement and wide application of wireless communication technology has penetrated into people's lives,which has an impact on people's lifestyle and brings great convenience.However,the development of wireless communication is bound to bring about an increasingly crowded spectrum resources and an increasingly complex electromagnetic environment.In order to achieve better signal transmission in the communication link,a series of more stringent demands are imposed on the microwave millimeter wave circuits and devices.As an irreplaceable frequency selective device in communication systems,microwave filters and multiplexers play an important role in preventing interference between closely neighboring channels and reducing noise figure.The performance will directly affect the quality of the entire communication system.Therefore,the research theory and design method of filters and multiplexers have been widely concerned and developed continuously.The research on microwave filters and multiplexers are mainly focused on the improvement of performance and the miniaturization of structure.The performance improvement generally refers to the reduction of the insertion loss of the filter,the enhancement of the passband selectivity,and the increase of the isolation between the multiplexer channels.And they are usually realized by improving the unloaded quality factor of the resonator and introducing transmission zeros at finite frequencies.The miniaturization of the structure is usually realized by reducing the frequency of the resonant mode or adopting the multi-mode mechanism.Based on the design theory of microwave filter and multiplexer,this dissertation aims to explore the research mechanism and design method of improving the performance and miniaturizing the structure.It can provide new ideas and solutions for the design of filter and multiplexer in wireless communication system.The work of this dissertation is mainly reflected in the following aspects:1.In order to improve the unloaded quality factor of the conventional suspended stripline resonator,a novel resonator structure is proposed.It adopts double-layer strips on both sides connected by a metallic via hole at the open end of the strips,minimizing the electric field distribution in dielectric substrate to reduce the dielectric loss and improve the quality factor of resonator.And based on the novel resonator,two sixth-order cross-coupled filters and a diplexer are designed.Subsequently,based on this resonator,the stepped impedance resonator loaded with a cuboid metal brick near the open end of the resonator is proposed to realize the miniaturization of the resonator structure.The relationships among the unloaded quality factor,the resonant frequency of the resonator,and the size of the structure are discussed from the perspective of equivalent circuit.The study provides a design method for the miniaturization of the suspended stripline resonator with a high unloaded quality factor.2.For some topological constraints,such as the case where the folded cross-coupled topology cannot be physically realized,an inline configuration with pseudoelliptic function frequency response needs to be realized.Therefore,the mixed electromagnetic coupling theory is deeply studied.Based on a synchronously tuned coupled resonator circuit with parallel resonant tank and admittance inverters,general formulas for extracting electric and magnetic coupling coefficients are derived,which has certain guiding significance for the design of mixed coupled filter.Meanwhile,based on the novel transmission line structure of substrate integrated suspended line,the systematic design procedure of the mixed coupled filter are given by a filter prototype with controllable transmission zeros.3.In order to obtain a wider stopband bandwidth and achieve miniaturization of the filter structure,a slot perturbed fan-shaped half-mode substrate integrated waveguide resonator is proposed based on the idea of multimode resonator.Firstly,an novel fan-shaped half-mold substrate integrated waveguide resonator is introduced.The resonance characteristics of the resonator are analyzed by the distribution of the electric field and surface current.Then the parameters of the size and position of the perturbed slot are analyzed,and the corresponding relationship between the electrical parameters and the structural parameters is obtained.At the same time,the design method of filters with different order is presented and validated.Due to the perturbation of the slot,some high-order mode current distributions are changed,which achieves the miniaturization of the resonator and a wide stopband bandwidth.According to the theory analysis and experiment validation,this kind slot perturbed substrate integrated waveguide filter can be easily extended to high-order filters without significantly increasing the complexity and size of the circuit,which makes it attractive in both academic and industrial fields.4.For the inline topology application scenario,the pseudoelliptic function frequency response can be realized by the mixed electromagnetic coupling mechanism.In some scenarios where it is difficult to construct a mixed coupling mechanism,the pseudoelliptic function frequency response can also be realized by introducing a non-resonating mode to construct a special coupling mechanism.Therefore,the non-resonating mode theory is deeply studied.The influence mechanism of transmission zeros has been analyzed and the equivalent topology is presented.Finally,a third-order filter with controllable transmission zeros is implemented by three dielectric resonators oriented along orthogonal directions and cascaded along an evanescent mode waveguide.The introduction and the mechanism of the non-resonating mode are analyzed in detail,having certain guiding significance for the design procedure.5.The design method of the multiplexer based on the multi-mode resonator is studied.Compared with the conventional star-point multiplexer,there is no need for a common matching circuit part in the multi-mode resonator multiplexer.And the different modes in the multi-mode resonator are independent of each other,so that the multi-mode resonator multiplexer can achieve good isolation at the output ports.The design of the multimode resonator multiplexer can realize the miniaturization of the structure,and it will have greater superiority with higher order.And the absence of the redundant matching circuit structure reduces the complexity of the design.Based on this idea,two triple-mode resonator triplexers are designed in the form of substrate integrated waveguide and dielectric resonator respectively,which provides feasibility verification for multi-mode resonator application in multiplexer design and is of great guiding significance.