Coplanar microwave filters with YBa 2Cu 3O 7− δ thin films on sapphire substrates

Abstract

A bandpass filter for a 1 dB relative bandwidth of 2.5% at 1.417 GHz is implemented with five end coupled resonators of meander coplanar lines with air bridges for ground connections on a 4.0×2.6 cm 2 substrate. A single sided sputtered YBa 2Cu 3O 7− δ film with a CeO 2 buffer layer on a sapphire substrate is patterned with an Ar ion beam. The wanted bandwidth of 35 MHz near 1.4 GHz is measured with a minimum insertion loss smaller than 0.1 dB at 15 K. Filters for a two channel receiver with almost identical characteristics have been fabricated without manual tuning screws. In the passband an insertion loss difference of less than 0.2 dB has been achieved. Their characteristics are not affected by mechanical vibrations on a cold finger. To attenuate higher order pass bands the design of a superconducting low pass filter is discussed.