Compact wideband double-layer half-mode substrate integrated waveguide 90° coupler

Presented are two novel double layer substrate integrated waveguide (SIW)-based couplers, the longitudinal-slots-based broadwall SIW coupler and its corresponding half-mode SIW coupler. Coupling takes place through a set of narrow, offset slots, which feature a flexible design providing a wide coupling dynamic range with wideband characteristics. This technique provides a compact design through both the double layer scheme and the half-mode structure. Isolation and input reflection characteristics better than 15 dB and 13 dB, respectively, are experimentally validated over 24% fractional bandwidth at 12.5 GHz. Measured coupling magnitudes and phases exhibit dispersive characteristics lower than 1 dB, and 8 degrees with respect to the adopted design values, respectively, over the entire frequency band.