ABSTRACT This letter presents an X/Ku‐band broadband bandpass filter (BPF) with high selectivity through collaborative design of hairpin ring resonators (HRRs) and feed‐line resonators (FLRs). An inverted cascade topology for HRR coupling serves dual purposes. It relocates transmission zeros to enhance stopband rejection and simultaneously achieves nearly threefold magnetic coupling enhancement, strengthening coupling for bandwidth expansion. HRRs provide wideband response through inverted cascade coupling, while FLRs simultaneously serve as impedance‐matched I/O ports while introducing supplementary transmission poles and independently tunable transmission zeros, FLRs integrate matching functionality within resonant structures, eliminating the need for separate external matching elements and achieving a measured 48.06% fractional bandwidth. Decoupled FLR geometric parameters enable independent zero control across both lower and upper stopbands without affecting passband integrity. The fabricated 10‐pole prototype demonstrates near‐ideal shape factor of 1.08 at a center frequency of 12.9 GHz spanning 9.8–16 GHz with four controllable transmission zeros providing superior stopband rejection, validating this collaborative methodology for wideband communication systems through excellent measured‐simulated agreement.
Liu et al. (2026) studied this question.