Miniaturized superconducting filter for mobile communications

Superconducting filters show many advantages over conventional filters such as higher selectivity, better out-of-band rejection and less interference between adjacent channels. Using ideas of a modified hairpin, the Chebyshev approximation and cross coupling between non-adjacent resonators, we have designed a 12-pole superconducting filter for centre frequency of 1.84 GHz and bandwidth of 5 MHz. The filter utilises YBa₂Cu₃O_7-δ films on a 58 mm × 14 mm × 0.3 mm LaAlO₃ substrate, 0.3 mm thick. The simulated passband insertion loss of the filter is 0.1 dB and the out-of-band rejection is 50 dB at 1 MHz from the passband.