A 9 pole bandpass filter at 2.7 GHz with Y1Ba2Cu3O7-δ 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 1.7×3.7 cm² substrate. A single side thermally co-evaporated Y₁Ba₂Cu₃O_7-δ thin film with a CeO₂ 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.