Three‐fourths‐mode substrate‐integrated waveguide for tri‐band bandpass filter

In this letter, a novel three‐fourths‐mode substrate‐integrated waveguide (TFMSIW) single‐band bandpass filter (BPF), and a TFMSIW tri‐band BPF are proposed for the first time. The resonant modes of a TFMSIW cavity are analyzed first to show their unload quality factors and both electric and magnetic field distributions. Based on the characteristics of the TFMSIW cavities, a single‐band BPF prototype is introduced. Moreover, with multiple coupling windows for respective passbands, a further application to tri‐band BPFs is studied. Consequently, two cases of tri‐band BPF are designed, fabricated, and tested for demonstration.