High CM suppression balanced SIW BPF and HMSIW directional coupler utilising perfect electric conductor/perfect magnetic conductor characteristic

Abstract

In this study, high common-mode (CM) suppression balanced substrate-integrated waveguide (SIW) bandpass filter (BPF) and half-mode SIW (HMSIW) directional coupler are formed by two vertically stacked identical SIW or HMSIW single-ended ones and an aperture etched on the common ground between them. Under CM operation, the aperture is perfect magnetic conductor (PMC). When the height is less than λ g/4, the space between perfect electric conductor and PMC cannot transmit electromagnetic wave and a total reflection is got at the aperture edge. So, the aperture structure in SIW can effectively cut off CM noise over a wide frequency range. For the HMSIW, the spoof surface plasmon polariton structure is further loaded in the aperture near the open circuit plane to suppress the slot line mode (main TE mode). The CM suppression can be basically made independent of differential-mode response, which is very important to simplify the design and tuning processes. Finally, high CM suppression balanced SIW BPF and HMSIW directional coupler are designed and fabricated. Good agreements between the simulated and measured results demonstrate the validity of proposed configurations.