HTSC quasi-elliptic linear-phase filter with prototype structure

A high temperature superconducting (HTSC) wideband filter with both quasi-elliptic and linear-phase response is directly designed by adopting prototype structure in this paper. At the same time, the open-gap's position in traditional square open-loop microstrip resonator is modified for the reason of adapting to the conventional aqueous photolithography technology. A six-pole HTSC linear phase filter which has a 55MHz pass band at a center frequency of 1995MHz is designed based on the prototype structure. The measured result is in very good agreement with the simulated result. The measured bandwidth of the filter is 55 MHz and the group delay variation is less than ±0.5 ns over 55% of the filter bandwidth.