Coplanar microwave filters with YBa2Cu3O7-δ thin films on sapphire substrates

A bandpass filter for a I dB relative bandwidth of 2.5% at 1.417 GHz is implemented with five end coupled resonators of meander coplanar fines with air bridges for ground connections on a 4.0 x 2.6 CM2 substrate. A single sided sputtered YBa2Cu3O7-delta film with a CeO2 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. (C) 2002 Elsevier Science B.V. All rights reserved.