Abstract: This paper presents a cruciform directional coupler, which is composed of two cross half mode substrate integrated waveguide (HMSIW) sections having two inductive metallic adjusting vias in cross region, and one matching via at each input/output port. Two adjusting vias can be used to adjust the coupling ratio and phase difference between coupling port and through port, while each matching via can be used to achieve a low return loss at input port. Compared with conventional substrate integrated waveguide (SIW) coupler, the metal size of the proposed coupler is reduced by half meanwhile its performance is maintained. The measured results are in agreement with the simulated results, which validates the concept of the HMSIW coupler and its design method.