HTS narrow band filters at UHF band for radio astronomy applications

High performance narrow-band High-Temperature Superconductor (HTS) filters at 610 MHz with very sharp cut-off response and low loss are needed for improving the observation of pulsars at the Jodrell Bank Observatory, UK. An eight-pole quasi-elliptic HTS filter using compact resonators has been designed for this purpose. The measured response of filter has an insertion loss of 0.3 dB (including a 0.2 dB ripple), and a return loss of 15 dB in the passband. Two transmission zeroes are realized to improve the steepness of the cut-off. The lowest harmonic is designed to appear at 1.79 GHz, about three times the center frequency. The out-of-band rejection is better than 85 dB up to this harmonic. The filter has been tested in the observatory with excellent results.