Research On Microstrip High-temperature Surperconducting Ultra-narrowband Bandpass Filter

With the rapid development of wireless technology,the limited spectrum resources are divided into narrower frequency bands to use,which leads to the serious situation of mutual interference between adjacent signals.In order to meet the needs of radio astronomy spectrum observation and weather radar observation,the demand of ultra-narrowband bandpass filter(BPF)is rapidly increasing and the performance of ultra-narrowband BPFs needs to be improved.Therefore,research on ultra-narrowband with low insertion and high selectivity has a great significance.In this dissertation,the design theory and circuit structure of high-temperature superconducting(HTS)filter with non-uniform line-width resonator and ring resonator are analyzed and studied.A variety of microstrip HTS ultra-narrowband BPFs are realized.Moreover,the dispersion characteristics and equivalent circuit models of dual-composite right/left-handed(D-CRLH)resonator are analyzed and studied,and narrowband bandpass filters with high square ring factor are designed.The main research contents and innovative achievements are as follows:Firstly,a single-spiral resonator using non-uniform line-widths is proposed.Through full-wave electromagnetic simulation,it is found that the resonator structure with gradual line-width design,the coupling strength of the single-spiral decreases faster than the double-spiral structure and can achieve weaker coupling within the same spacing.And the single-spiral resonator is used as the resonance unit to design a two-pole ultra-narrowband BPF.In order to meet the needs of highly selective applications,high-order expansions are designed using gradient line-width resonators.The six different types of regular coupling between adjacent resonators can be found by analyze the current diagram at the resonant frequency,and then,the compact resonator unit that is most suitable for the design is obtained.And lastly a sixth-order HTS ultra-narrowband filter with equal ripple of 0.0432 d B and fractional bandwidth of 0.17% is designed and measured.The proposed BPF is fabricated and measured,the measure results are consistent with the simulation ones.Secondly,a novel HTS ultra-narrowband filter based on uniform impedance stub-loaded ring resonator is proposed.Firstly,the resonance mode distribution of the traditional ring resonator is simply analyzed.The folding coupling line technology is used to fold the ring resonator to a certain extent to achieve miniaturization and weak coupling;Secondly,in order to further achieve weak coupling,a new type of dual-ring resonator is formed by loading U-shaped branches.Finally,based on the novel dual-ring resonator,a six-pole HTS ultra-narrowband bandpass filter with an equal ripple of 0.0432 d B and fractional bandwidth of only 0.04% is developed.Thirdly,a dual-band narrow-band filter is designed by using a novel D-CRLH resonator structure.The first step is to introduce the traditional D-CRLH resonator,and the single-mode and dual-mode D-CRLH resonators based on the design are proposed and analyzed.And then the equivalent circuit model of the dual-band BPF is established,which simplifies the design process of dual-band BPF.At last,to accommodate modern multi-band communication applications,a dual-band HTS narrowband BPF with independent control of coupling coefficient and frequency is designed.The dual-band HTS BPF operating at 0.89 and 1.74 GHz,and fractional bandwidth of 1.67% / 1.7%,is fabricated and measured at 77 K,the measure results are consistent with the simulation ones,which verifies the design schemes proposed in this dissertation.Meanwhile,a good foundation of theory and practice will be established for the research and its application of the dual-band ultra-narrowband filter.