Research On Hts Lowpass Filters And Super High Frequency Bandpass Filters

High temperature superconducting(HTS)filters with low insertion loss and high band edge steepness have been widely used in mobile communication,radio astronomy and satellite detection systems.Because of the shortage of the spectrum resource and the working frequency band moving close to high frequency,wide stopband lowpass filters and bandpass filters at super high frequency with excellent performance are in great demand.This dissertation proposes a novel compact lowpass filter which adds an ‘E' shape structure between the feedline and the coupled-line.A cross-shape patch is loaded at the other end of the coupled-line.Both of the passband and the stopband show high performance.The filter is cascaded after a four-pole bandpass filter.The spurious passband in range of three times ce nter frequency is suppressed remarkably.This filter has the value of practice of engineering application.This dissertation focuses on the common problem of uncontrollable transmission zero in X-band filter design when using rectangular resonators.By optimizing the rectangular resonators from the loop structure with a small opening to the double-folded one,weak couplings between resonators are obtained.A six pole HTS filter with high performance at X-band using doublefolded resonator is designed and fabricated to demonstrate the weak coupling performance of double-folded resonator.There is no transmission zero appears on the low-frequency side of the passband as expected.The proposed resonator can be further used in designs of diplexers and multiplexers for X-band microwave applications and narrow band filters at higher frequencies.HTS wideband filter at super high frequency is systematically studied in this dissertation.Methods for enhancing the coupling between resonators have been discussed.A microstrip resonator consisting of an H-shaped main line part with both ends installed with interdigital finger parts,is proposed for the wideband filter design.Strong electric coupling is achieved without introducing vertical spurious coupling.A six-pole high-temperature superconducting filter at Ku-band using this resonator is designed and fabricated.The filte r has a center frequency of 15 GHz with a fractional bandwidth of 30%.As far as the author knows,this filter has the largest fractional bandwidth among the publications about wideband filters at Ku-band.All the research results discussed above have important value in both academic and engineering applications.