A Compact HMSIW Coupler Based on Slow Wave Structures

Abstract

A new slow-wave structure is proposed in this article to miniaturize the half mode substrate integrated waveguide (HMSIW). Consequently, SW-HMSIW in this article achieves a reduction about 66.81% of the SIW transverse dimension. Moreover, the phase velocity in HMSIW declines by 66.7% at the wanted frequency, which corresponds to the reduction of the longitudinal dimension. Based on SW-HMSIW, a compact Riblet-type directional coupler for 3-dB coupling is fabricated and measured. The measured S31 is about −3.56 (±0.5) dB at 7.5 GHz covering a fractional bandwidth of 28.32% while the isolation is better than 15 dB. And the area of the coupler is only 0.524λg2.