Research On Advanced Synthesis Theory And Novel Topologies For Microwave Filters

Filter synthesis is a procedure that determines both the topology and element values,resulting in an ideal circuit prototype for a microwave filter.Advanced synthesis theory can not only properly guide the implementation,fabrication,and tuning for physical filter design,but also bring in innovative solutions for the increasing performance requirements of a microwave filter;for these reasons,the filter synthesis is considered as the base step in the filter design.With the developing of modem communication systems,there comes more significant challenges for microwave filters,both in structure characteristics and performance characteristics.In this dissertation,three of the most urgent challenges of microwave filter synthesis are discussed respectively,i.e.,the synthesis for novel integrated passive networks based on filtering functions,the synthesis for novel filters with flexibility on generating&controlling transmission zeros(TZs),and the synthesis on novel in-line topology filters with high frequency selectivity.Main work and contribution of this dissertation is as follows:A new generalized filter synthesis theory is proposed for the first time,which defines a new network named as generalized filtering network that integrates the design of traditional filter,impedance matching network,and ideal phase shifter as an entity.Based on the new required S parameters,the relevant admittance functions is derived,introducing a novel transversal array network that possesses non-resonating nodes(NRNs)at reasonable positions.According to the new definitions for coupling values,a new coupling matrix is finally observed.As the functions of traditional filter,impedance matching network,and ideal phase shifter are now described by a single matrix,it implies that the proposed approach can observably reduce the whole size,design complexity,and insertion loss for RF front-ends.Based on the former proposed generalized filtering network,the dissertation presents a new technique that generates the extracted-pole structures from transversal array network automatically.With a novel admittance parameters&topology reconstruction solution,a direct coupling matrix approach is introduced for the first time to synthesize mixed topology filters(where one or more extracted-pole structures are involved,separately).Note that all the coupling elements can be determined one time here,which significantly improves the efficiency and reduces the round-off errors,compared with the literatures;it can be inferred that this approach provides the best synthesis solution to realize novel filters with flexibility on generating&controlling TZs.Frequency variant couplings are introduced in the in-line topology synthesis for the first time,which presents a novel direct approach for in-line filters with TZs generated by frequency-variant couplings.On the basis of a rescaling principle for frequency variables,the transformation from the transversal array(with only constant couplings)to the novel in-line topology is recommended.It is shown that,based on the presented approach,in-line filters with high frequency selectivity are synthesized for the first time,which effectively minimizes the circuit elements and coupling numbers to realize TZs.