A compact two-pole X-band high-temperature superconducting microstrip filter

In this paper we examine a microstrip line filter with three gaps separated by approximately a quarter wavelength. Two filters, one with gold and the other with YBCO were fabricated. The thickness of top conducting microstrips was 600 nm. The ground plane under the 0.5 mm-thick lanthanum aluminate (LaAlO/sub 3/) substrate was implemented with a 2 micron-thick gold layer for both filters. These filters showed similar frequency responses with 5% 3-dB bandwidth. The insertion loss, however, improved from 2.8 dB to 1.5 dB by using the superconductor. The performance of the filter was also tested by employing the three dimensional microwave FEM software, and the simulation result compared well with the measured data.>