Design for transmit bandpass filter and trimming method using superconducting bulk ring resonator and dielectric rods

We designed transmit bandpass filters (BPFs) by using superconducting bulk ring resonators and dielectric trimming rods at a 5.0 GHz center frequency with a 100 MHz bandwidth. The filter with ring resonators was smaller than the filter with disk resonators, where the size was defined as the distance between the input/output ports. We found that the size contributes significantly to the miniaturization of multi-pole filters. A trimming mechanism was also evaluated. The frequency shift region of a single ring resonator reached more than 500 MHz after we moved a dielectric rod whose dielectric constant was 39 into the ring resonator. A 3-pole strip-line BPF was also designed using a Chebyshev function by using three pairs of ring resonators and dielectric trimming rods with the same dimensions and by adjusting the positions of the trimming rods. We obtained the optimal frequency response with a low loss and passband ripple for this BPF.