Superconducting filters based on mixed resonators

In high-temperature superconducting (HTS) microwave filters, the requirements for miniaturization and high power handling are difficult to match simultaneously. In this paper, we report on the design and realization of HTS filters realized by combining dual-mode cross-slotted and stepped resonators in order to obtain a compact size and a relatively high power handling. Prototype HTS four-pole filters operating in C-band and L-band, with quasi-elliptical responses, on both MgO and LaALO(3) substrates, have been designed and tested at T = 77 K. The filters present a high degree of miniaturization as they save more than 50% of the area compared with those realized with dual-mode and/or hairpin resonators. The measured responses agree well with the simulation even if the in-band ripple should be optimized. As far as the power handling is concerned, the C-band filter grown on LaAlO3 presents a power handling of P-in = 20 dBm limited by the power handling of the dual-mode cross-slotted resonator, while we have observed no power degradation in the L-band filter grown on MgO up to P-in = 33 dBm limited by power supply.