Substrate Integrated Waveguide Filter with Higher-Order Modes Suppression

In this paper, two methods to suppress the higher-order modes in substrate integrated waveguide (SIW) cavity are proposed. One is to use double coupling irises instead of single iris between two cavities, which prevents the TE
₃₀₁
mode from being excited effectively. The other is to etch narrow slots on the metallic plate of cavities, which destroys the TE
₁₀₂
mode. The theories of suppression are analyzed and the simulation results are also presented. In order to verify the methods, a SIW filter with the center frequency of 20 GHz is designed. The measurements show that the first spurious appears at about 50 GHz, which is 2.5 times of the center frequency.