A 9 pole bandpass filter at 2.7 GHz with Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// coplanar wave guides on a sapphire substrate

A bandpass filter for a 0.6 dB relative bandwidth of 4.5% at 2.67 GHz is implemented with nine end coupled resonators of meander lines with air bridges for ground connections on a 1.7/spl times/3.7 cm/sup 2/ substrate. A single side thermally co-evaporated Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin film with a CeO/sub 2/ buffer layer on a sapphire substrate is patterned with an Ar ion beam. Within a bandwidth of 112 MHz at 2.67 GHz the measured insertion loss is smaller than 0.1 dB at 15 K. Filters for a two channel receiver with almost identical transfer functions have been achieved without manual tuning screws. Their characteristics should not be affected by mechanical vibrations on a cold finger.