On the development of superconducting microstrip filters for mobile communications applications

This paper presents recent developments of an eight-pole planar high-temper ature superconducting (HTS) bandpass filter with a quasi-elliptic function response, A novel planar filter configuration that allows a pair of transmi ssion zeros to be placed at the band Edges is described, The miniature HTS filter has a fraction bandwidth less than 1% and is designed for mobile com munication base-station applications to increase sensitivity and selectivit y. Design considerations including filter characteristics, design approach, sensitivity analysis and unloaded quality factor of resonators are address ed. The filter was fabricated using double-sided YBCO thin film on an MgO s ubstrate of size 0.3 x 22.5 x 39 mm, Very good experimental results mere ob tained with the filter cooled using Liquid nitrogen. The minimum passband l oss was measured to be approximately 1 dB. The passband width at points 1 d B dawn from the minimum loss point was 12.8 MHz for a center frequency of 1 738.5 MHz, High selectivity was achieved with a 30-dB rejection bandwidth o f 16 MHz.