Novel Compact Quad‐Band HMSIW BPF and FPD With Low Loss and Tunable Passbands

This work introduces a new quad‐band bandpass filter (BPF) and filtering power divider (FPD) based on half‐mode substrate integrated waveguide (HMSIW) technology and metamaterial concept. To achieve a high level of miniaturization, multiple design approaches are jointly employed, including HMSIW implementation, evanescent‐mode operation, stepped‐impedance resonators (SIRs), fractal geometries, and the meandered technique. Using the aforementioned design strategies, quad‐band HMSIW BPF and quad‐band HMSIW FPD with equal power‐splitting characteristics were developed. These circuits operate at center frequencies of 1.75, 3.3, 4.5, and 5.2 GHz and were thoroughly validated through simulation, fabrication, and experimental measurement. The passband center frequencies are readily tunable through dimensional adjustments. Experimental results closely match the simulated responses. Moreover, the proposed structures occupy an extremely small footprint, with an overall size below , clearly demonstrating the high level of miniaturization achieved. The proposed structures offer several notable benefits, including a highly compact footprint, low insertion loss, tunable passband characteristics, reduced manufacturing cost, straightforward integration with planar microwave circuits, acceptable return loss performance, and flexible tuning of the operating center frequencies.