High temperature superconducting 8.45-GHz bandpass filter for the Deep Space Network

A high-temperature superconducting (HTS) stripline 8.45-GHz bandpass filter, designed for the Deep Space Network, is presented. It has very low insertion loss, indicative of resonators with unloaded Q's greater than 10000. The performance of this filter shows that practical, high-Q multiresonator devices can be constructed using lanthanum aluminate substrates in a stripline configuration. The HTS films used in this filter were of the thallium barium calcium copper oxide (TBCCO) variety, deposited on a lanthanum aluminate substrate using laser ablation and postdeposition thermal processing. The HTS surface resistance of these TBCCO films is less than 0.5 m Omega at 10 GHz and facilitates the construction of planar HTS resonators with unloaded Q's greater than 10000 at 10 GHz. HTS planar circuits with these Q's are very useful in constructing narrow-bandwidth filters due to the resulting very low minimum insertion loss.<>