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 TE102can be suppressed thanks to the proposed weak coupling or mixed coupling schemes in connection with the TE102mode. 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 TE102mode frequencies are below -30 dB and -20 dB for Filter I and II, respectively. Furthermore, simulated and measured results also show a good agreement.