A self-equalized HTS filter for future mobile communication applications

A 10-pole self-equalized high-temperature superconducting (HTS) filter is presented in this paper. The filter has a fractional bandwidth of 0.51% at 1955 MHz, simulated in Sonnet, and is fabricated using double-sided Tl2Ba2CaCu2O8 film on 0.5 mm thick LaAlO3 substrates. The filter consists of 10 novel quasi-lumped resonators and an additional microstrip which is used to realize the real-axis transmission zeros (TZs). The simulated group delay ripple over the central 55% of the filter’s passband is 5.6 ns, and a close result of phase response is achieved in laboratory test. The measured insertion loss of the filter is less than 0.2 dB, the out-of-band rejection is better than 75 dB and the slope is better than 22 dB MHz−1 at band edge.