The Design And Fabrication Of High-Performance High-Temperature Superconducting Filters

High-performance superconducting filters are widely used to improve the communication quality in some special communication systems such as electronic warfare,radio astronomy,and deep space exploration due to the low insertion loss,high out-of-band rejection,and good frequency selectivity.Nowadays,the microwave frequency resources are increasing in demand,which leads to severe interferences between adjacent bands.Therefore,more and more research interests are attracted to improve the filter performance in communication systems,and to reduce the interference between systems and the environment.This dissertation mainly introduces the design and fabrication of high-performance superconducting filters.The design and optimization of a high-performance filter for Bei Dou Navigation Satellite System(BDS)are presented first,and then the ultra-wideband filter design theories are discussed,tested,and proved in the second place.The main works are presented as follows:Bei Dou Navigation Satellite System relies on the earth-to-satellite communication,where the uplink and downlink signals suffer from the influences of the complicate electromagnetic environment.High-performance filters are needed to reduce the influences and to enhance the system stability.A high-performance superconducting filter for the BDS is designed and fabricated with coupled resonators circuit and quasielliptic function.The design of resonators and circuit structures,as well as the cross couplings and coupling properties are presented in the first place.And then,a remarkable upgrade is performed to improve the out-of-band rejection by redesigning the circuit and resonators structures.Moreover,a second optimization is applied to minimize the filter size so as to reduce the weight,size,and power consumption of the whole communication system.The filter size is reduced to less than half of that before by simplifying the circuit structure,reducing the linewidth of resonators,and reorganizing the cross coupling.Consequently,the filter can be integrated into a miniaturized cryocooler to achieve a lighter and smaller communication system.A novel and systematic wideband filter design method is put forward to solves several deficiencies of the existing wideband filter designs.The proposed design derives from lumped filter circuit and quasi-lumped microstrip elements,to avoid using the traditional coupling matrix which is valid only for narrow band filters.The out-ofband rejection can be improved by raising the filter order,which solves the shortcoming of traditional multi-mode wideband filters.Finally,the lumped circuit combines the lowpass filter circuit and the high-pass elements on one chip,without external cascading and grounding structure,the proposed filter guarantees a low insertion loss and high stability.Filters can be designed in varieties of method,so as resonators and circuits.The author performed some simulations on the ultra-wideband filters presented above,which reveals the inner connections among the quasi-lumped filter circuit,the multimode resonator circuit,and the coupled resonators circuit filter.EM simulations on current density and charge density distributions are presented to prove the results.The proposed quasi-lumped wideband filter can be regard as a dual-mode resonators circuit.Meanwhile,a single dual-mode resonator can be regard as a pair of coupled resonators,thus the coupling matrix can be applied to simplify the filter design.Different theories exhibit advantages in different situations and explain the emerging of each transmission poles and zeros.Several filter designs with compact sizes,wide passbands,high outof-band rejections,and low insertion losses are presented in the end.This dissertation discusses the performance improvement of high-order filters in stopband suppression and size reduction in the first place.And then,an ultra-wideband(UWB)bandpass filter(BPF)design theory based on lumped bandpass filter circuit is put forward.The model construction and measurement verification of an UWB filter based on multi-mode resonators are presented in the end.Important progress has been made in the design and research of superconducting filters.