High-order superconducting filter with group delay equalization

This paper reports recent development of an eighteen-pole high temperature superconducting (HTS) bandpass filter with group delay self-equalization. The filter is designed to have a 15 MHz pass band at a center frequency of 1967.5 MHz. The filter exhibits a quasi-elliptic function response implemented with a cascaded quadruplet coupling structure. Two particular cross coupled quadruplet realizations have been developed to implement either attenuation poles at finite frequencies or linear phase for group delay self-equalization. The filter was fabricated on a 0.43mm-thick sapphire wafer with double-sided YBCO films. Measured responses are presented to demonstrate the validity of the design as well as the potential of the filter.