Design and tuning of superconducting filter at VHF‐band with mechanically switchable interdigital capacitors

A tunable superconducting resonator consisting of a microstrip spiral and an 8‐bit switchable interdigital capacitor array, controlled by eight mechanical switches, is presented. The measured tuning range of the resonator is 1 MHz from 198.2 to 199.2 MHz with a fine average resolution of 4 kHz and an unloaded Q of over 55000. A four‐pole narrowband superconducting filter at 198.7 MHz with 0.2% fractional bandwidth is designed with this resonator and fabricated. By changing the states of the mechanical switches, the resonant frequency of each resonator and hence the frequency response of the filter is successfully tuned.