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.<>