Multilayer Substrate Integrated Waveguide (SIW) Filters With Higher-Order Mode Suppression

This letter presents a multilayer approach for suppressing the higher order modes of substrate integrated waveguide (SIW) bandpass filters. Rectangular SIW resonators in multilayer substrates can be vertically coupled with magnetic and/or electric coupling by the proposed apertures etched on the middle metal layer. Harmonic passbands produced by the first higher-order mode TE
₁₀₂
can be suppressed thanks to the proposed weak coupling or mixed coupling schemes in connection with the TE
₁₀₂
mode. Compared with conventional horizontally coupled filter, the proposed filters also show a compact physical size. To demonstrate the proposed design method, two double-layered SIW bandpass filters Filter (I and II) are fabricated and measured. The experimental results show that the maximum rejection levels at the TE
₁₀₂
mode frequencies are below -30 dB and -20 dB for Filter I and II, respectively. Furthermore, simulated and measured results also show a good agreement.