The Development Of High-temperature Superconducting Linear Phase Filter

The microwave filters using HTSC (high temperature superconductivity) thin films that are small in size and mass have the advantages of low resistance and high quality factor, so it's performances are much better than the filters using wave-guide,dielectric resonance or conventional planar structures, offers the potential of large reduction in mass and volume of communication systems, and lead to significant cost reduction of communication systems. This paper presents the characteristics of HTSC materials and analyzes the using of HTSC filters, then gives the theory of HTSC linear phase filters. The modes of HTSC resonance and filters have been built using CAD programs by full-wave field solvers. Then a HTSC filter according to the aim of designs has been synthesized, manufactured, installed and measured. In this paper, difficulties such as the design of HTSC microwave passive component,the lithography process technology,the encapsulation and the measurement in low temperature and so on have been solved. With a special transfer function changed from a six-pole quasi-elliptic function by extracted pole, on YBCO/LaAlo3/YBCO substrate, a HTSC filter having a bandwidth of 80MHz, which center frequencies is 1.75GHz , the insertion loss is less than 0.2dB and the group delay fluctuation is less than 2ns,has been designed, and measurement results satisfied the requires of designs. There is no report about HTSC linear phase filters in our country now.