Compact Diplexer With High Isolation Using the Dual-Mode Substrate Integrated Waveguide Resonator

This letter presents a substrate integrated waveguide (SIW) diplexer using the dual-mode resonator. By enhancing the perturbation strength, the resonant frequencies of the dual-mode square cavity can be assigned to required frequencies. Thus, the cavity can be employed as the common resonator to replace the T-junction. The coupling aperture between the common resonator and the triangular resonator is parallel to one resonant mode's magnetic field and perpendicular to the other's. As a result, the isolation between the two channels is increased. Furthermore, the cavities are vertically stacked to realize a compact size. A diplexer with lower and upper channels centered at 8 and 9 GHz, respectively, is designed to verify the proposed concept. The simulated and measured results agree with each other.