Research On UHF Band High Temperature Superconducting Filter

With the rapid development of mobile communication technology,the requirements for filters in microwave systems are getting higher.Ordinary filters are usually made of silver,copper and other metals with a certain resistivity,which have disadvantages of low quality factor and high in-band loss.So their performance is more and more difficult to meet the needs of use.High temperature superconducting filters,which are made of superconducting thin films with very low microwave resistance,have the advantages of low insertion loss and high frequency selectivity,and have attracted wide attention.This paper mainly focuses on the design and research of Ultra High Frequency(UHF)band superconducting filter and its system.This band is located in the low frequency region of microwave band.TV and radio signals are concentrated in this band.The electromagnetic environment is very worse,so it is meaningful and necessary to carry out relevant research.The specific contents and research results of this paper are as follows:(1)The basic theory of coupled filters and the synthesis method of coupling matrix of generalized Chebyshev filters are described in detail.Based on the theories and methods,three design methods of superconducting filters are summarized.(2)An interdigitated resonator suitable for weak coupling is proposed.The resonator not only has a compact structure,but also can effectively push parasitic passband upward,A 15-order narrow-band superconducting filter for UHF radar receiver front-end is successfully developed and tested on a 2-inch superconducting thin film using the resonator.The test results show that the filter has excellent frequency selectivity,the band edge steepness is about 85 dB/MHz,the wide-band out-band suppression is more than 85 dB,and the parasitic passband is pushed up to 3.3 times the fundamental frequency.(3)A broadband superconducting filter for UHF radar receivers has been successfully developed on a 2-inch superconducting thin film using a new resonator suitable for strong coupling and a novel cross-coupling structure.The filter is tested and the test results show that the relative bandwidth of the filter is as high as 22.83%,and it also has high rectangular coefficient and flat group delay fluctuation.The rectangular coefficient(BW40dB/BW1dB)is 1.246,and the group delay fluctuation in passband is less than 35 ns.(4)A new superconducting filter integrated system for phased array radar is proposed.According to the structure of phased array radar,the integrated system is calculated and designed.The system can effectively reduce the volume and weight of the superconducting filter system in microwave receiver.It has the advantages of easy maintenance,high stability and easy integration.(5)Based on the new superconducting filter integrated system,the design of broadband preferred filter and narrowband filter banks for phased array radar receiver is completed by using a variety of resonators and cross-coupling structures.The design results are better than the requirements of the system.