Tunable Quasi-Reflectionless Bandpass Filters Using Substrate Integrated Coaxial Resonators

This brief reports on the electromagnetic (EM) design and the practical development of frequency-reconfigurable quasi-reflectionless bandpass filters (BPFs) using substrate integrated coaxial (SIC) resonators. The filter concept is based on in-series-cascaded quasi-reflectionless stages that are shaped by a first-order bandpass section and two resistively-terminated first-order bandstop sections. For the first time, we explore the realization of these filters using tunable SIC resonators that exhibit high quality factor (
${Q}$
) and can be widely tuned with commercially-available linear piezoelectric actuators. Synthesized examples alongside various EM design and practical integration aspects are discussed in detail. The concept is experimentally validated at S-band through the manufacturing and testing of two reconfigurable (one-stage and two-stage) prototypes.