Аннотация:In the microwave band, substrate integrated waveguide (SIW) couplers take the advantages of low profile, low insertion loss, low interference etc., but suffer from the big size. In this letter, a novel half mode substrate integrated waveguide (HMSIW) 3-dB coupler is proposed, which keeps the good performance of the SIW coupler with nearly a half reduction in size. Simulated results are in agreement with the measured data