Design of Compact Multilayer Differential CSIW and HMCSIW With High Common-Mode Suppression

In this letter, the compact multilayer differential corrugated substrate integrated waveguide (CSIW) and half-mode CSIW (HMCSIW) are designed by two vertically stacked identical CSIW and HMCSIW, respectively, and an aperture is etched on the common ground between them. Both the CSIW and HMCSIW have only one nonzero vertical electric field component in host waveguide. Under the common-mode (CM) operation, the aperture is a perfect magnetic conductor (PMC). When the height of the single substrate is less than lambda(g)/4, the space between the perfect electric conductor (PEC) and PMC cannot transmit electromagnetic waves, and the edge of the aperture is an open circuit. Therefore, the etched aperture in differential CSIW can effectively cutoff CM noise. For the HMCSIW, the spoof surface plasmon polariton (SPP) is loaded in the aperture near the open circuit plane to suppress the slot line mode. Under the differential-mode (DM) operation, the aperture has less effect on the DM frequency responses. For verification, the differential HMCSIW is fabricated, and good agreement between the measured and simulated results demonstrates the validity of proposed configurations.