In‐Line Bandpass Filters With Flexible Transmission Zero Distribution Using Asymmetric Dual‐Behavior Resonators

ABSTRACT We propose in this letter an analytical method for realizing bandpass filters with N reflection zeros (RZs) but more than N transmission zeros (TZs) that are flexibly (symmetrically or asymmetrically) positioned outside the passband. The approach relies on the development of asymmetric dual‐behavior resonators at lowpass domain, accommodating one reflection zero (RZ) and two asymmetric TZs. These asymmetric DBRs are then properly adopted into an in‐line prototype, allowing them to be cascaded with conventional resonators via constant or frequency‐variant couplings. To provide a planar solution, we also introduce practical distributed models of the asymmetric DBRs where all elements are properly determined to meet the required in‐band and out‐of‐band performances. For validation, an experimental example is carried out with microstrip implementation, along with reasonable responses.