Enhanced dual- and triple-band bandpass filters using slot-line perturbed HMSIW resonators

This paper designs dual- and triple-band bandpass filters (BPFs) using half-mode substrate-integrated waveguide (HMSIW) resonators with slot-line perturbations. Subsequently, the resonance and coupling characteristics of the perturbed HMSIW resonators are analyzed. A dual-band BPF featuring the TE100 and TE102 modes, with independently tuned passbands, is realized through the incorporation of inner coupling slot lines and metal-hole rows to compensate for external coupling effects. Furthermore, input/output matching is achieved through the inset feedings of a quasi-coplanar waveguide, simultaneously exciting the desired modes. The total layout features a size of 0.725λg × 0.44λg. Building upon this dual-band BPF design, a novel triple-band BPF is realized by incorporating three additional slot lines to excite the higher mode (TE103) for the third passband and control the second passband. Both BPFs are simulated, fabricated, and examined. Results reveal that the designed BPFs exhibit low insertion losses (<1.8dB), along with return losses better than 14dB. The adjacent passband isolation of both filters exceeds 20dB, and stopband high rejection is achieved by introducing more than three transmission zeros. Overall, the experimentally measured results demonstrate good agreement with the simulated ones.