Half Mode Substrate Integrated Waveguide 180° 3-dB Directional Couplers

In this paper, two types of half mode substrate integrated waveguide 180° couplers are proposed, the phase-shifting structures of which are composed of metallic via fins or etched air slots. Each coupler maintains the good performance of the substrate integrated waveguide coupler with a half reduction in size and a 180° phase difference between through and coupling ports. Prototypes working in the $C$-, $X$-, $Ku$-, and $Ka$-bands are designed and fabricated using the standard printed circuit board process. The consistency between the measured data and simulated results shows that the proposed couplers have the merits of low profile and good performance.