A design of the tunable superconducting power filter is described. The filter consists of superconducting microwave cavities with a mechanical tuning method. The electromagnetic simulations using niobium cavity suggested that there were conditions where the resonator with high-unloaded Q can realize a fractional center frequency change of more than 10% by using a Nb rod moving in the cavity. The simulations approximated the resonant frequency dependence of the rod moved by a cryogenic actuator in the tunable cavity experiment. In addition, the simulation of the power handling capability showed a feasibility of the value more than 50 dBW.

We report on suppressing adjacent-frequency interference (AFI) by using a RF receive bandpass-filter (BPF) with high-selectivity. By considering a high temperature superconducting (HTS) multi-pole BPF as a high selective BPF, the effect was estimated by numerical simulations. The simulations of the RF signals with an OFDM modulation transmitted to the demodulator via the BPF were carried out using the HTS BPF for 5 GHz band. The results confirmed the improvement of the bit error rate (BER) characteristic with the assumed HTS BPF with the high multi-poles under a strong AFI.

We report on the spurious suppression effect in low-microwave power transmitters by high temperature superconducting (HTS) bandpass filters (BPFs) which are promising for devices requiring BPFs with high-frequency selectivity. Some of the major issues on the power BPFs with HTS planar circuits for wireless communication applications are reviewed. As a case study for the HTS filter and its spurious suppression effect, this paper describes an example of the measured power spectrum density (PSD) on the suppression effect by one of our developed power BPFs with YBCO films for the 5 GHz band. It was designed with equivalent cascade resonators of 16 poles. We demonstrated the effect by HTS power filter in a power amplifier for the 5 GHz band.