Substrate Integrated Folded Waveguide (SIFW) narrow-wall directional coupler

For low microwave band, the size of substrate integrated waveguide (SIW) couplers still need to be further reduced though other advantages of low profile, low insertion loss, low cost etc. are very remarkable. In this letter, novel substrate integrated folded waveguide (SIFW) narrow-wall single-slot and double-slot directional couplers are designed and implemented. The measured results are in good agreement with simulations. A corresponding SIW coupler is also designed for comparison. The SIFW coupler keeps almost all the advantages of the SIW coupler with nearly a half reduction in size.