High temperature superconducting filter with linear phase on LaAlO3 substrates

A linear phase high temperature superconducting HTS filter fabricated on LaAlO3 substrates is presented. The designed passband of the HTS filter is 10 MHz and the group delay ripples over 80% of the passband is less than 20 ns. The filter consists of novel resonators, which are able to minimize the spurious couplings between resonators. As a result, the filter shows not only the linear phase characteristic but also the symmetrical frequency response. The measured passband is 9.85 MHz. The return loss is better than 16 dB and the out-of -band rejection is better than 80 dB. The measured group delay ripples is about 20 ns, which is in good agreement with the simulated result.