Design of sextuple-mode triple-ring HTS UWB filter using two-round interpolation

A single-stage ring resonator capable of introducing six modes within the ultra-wideband(UWB)passband is presented.The sextuple-mode resonator consists of three rings and three sets of stepped-impedance open stubs.Based on this sextuple-mode resonator,a UWB filter fed by the interdigital-coupling line(ICL)is designed.And we propose a two-round interpolation method to obtain the filter's initial dimensions.The designed filter is fabricated on a double-sided YBCO/MgO/YBCO high-temperature superconducting(HTS)thin film for demonstration.The experimental results show that this UWB filter produces eight resonances in the passband eventually,which effectively improves the in-band reflection and the band-edge steepness.Moreover,the upper stopband performance is enhanced due to the transmission zeros(TZs)generated by the stepped-impedance open stubs and the ICL structure.The measured good performance verifies the practicability of the two-round interpolation approach,which can also be extended to other odd-even-mode filter designs.

Switchable and tunable triple-channel bandpass filter

A triple-channel bandpass filter with switchable and tunable functions is proposed,which is based on a triple-mode cross resonator.The varactors and switching diodes are loaded at the end of the resonator.Because of the use of switches,resonators have four working states:conventional single-mode,two dual-modes,and one triple-mode.The varactor makes the channel independently adjustable.Finally,a triple-channel bandpass filter with switchable and tunable functions is designed by using two identical triple-mode resonator coupling structures.To solve the problem of whether each channel in the multi-channel filter is independently adjustable,this paper gives a simple and rigorous judgment method,namely rank criterion,which is a necessary and sufficient condition for each channel to be independently adjustable.The method of designing an element variable coupling matrix(EVCM)is adopted,which can not only obtain the desired frequency response through adjustable elements but also help to select resonators and coupling modes in the actual circuit design.The final circuit size of the designed filter is 0.29λg×0.26λg.The measured results are in good agreement with the simulation results.