Tl/sub 2/Ba/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ thin films for microstrip filters

High performance narrowband bandpass filters are required in satellite communication systems. Especially HTS filter banks are particularly attractive because of their low insertion loss and sharp filter skirts needed in input multiplexers. Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub x/ thin films on 2"-LaAlO/sub 3/-substrates and 10/spl times/10 mm/sup 2/-sapphire substrates were prepared using a two step technology. A Tl-free precursor film is prepared by sputtering. The Tl-incorporation is performed by annealing in a Tl/sub 2/O loaded atmosphere. The best films show surface resistances below 100 /spl mu//spl Omega/ at 77 K and 4 GHz. Two-pole bandpass-filters with a center frequency of 4 GHz and a bandwidth of 17.5 MHz using dual-mode ring resonators have been fabricated from the films on LaAlO/sub 3/. The measured passband shape achieved with tuning elements is in good agreement with the specifications of the design.