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

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.