Multilayer Cross-Coupled SIW Filter with Next Harmonic Suppression

In this paper, substrate integrated waveguide (SIW) filters with multilayer configuration are presented. Such configurations reduce circuit footprint area without compromising the passband loss. Here it is shown that a metallic post can provide magnetic as well as electric coupling. Further, it is shown that proper placement of the slots, used here to obtain coupling between two adjacent layers, can provide next harmonic suppression. Finally, a four-pole prototype is designed which provides symmetrically placed transmission zeros. The filter offers a measured insertion loss of 1.55 dB at f0=2.20 GHz. The stopband rejections are at least 40 dB at (f0 ± 0.2) GHz and the next harmonic is suppressed at least by 28 dB.