Design of Compact and Wideband Groove Gap Waveguide-Based Directional Couplers

This paper proposes a compact cross-shaped groove gap waveguide structure for creating wideband and compact directional couplers with different coupling levels. Groove gap waveguide technology is applied to overcome fabrication challenges of printed and hollow waveguide structures in high frequency bands. The validity of the novel concept is demonstrated through the design and evaluation of several compact broadband directional couplers, featuring 3-, 4.5-, 6-, and 10- dB coupling levels, alongside the fabrication and testing of a compact, wideband 3-dB directional coupler prototype. In addition, an equivalent circuit is proposed to present the behavior of the 3-dB coupler. The comparison of simulation and experimental results for the prototype shows good agreement. The measured transmission coefficients in the output ports are
$- 3 \, \pm \, 0.5$
dB with a phase imbalance of
$\pm \, 2.5^{\circ }$
over 17.9-24 GHz frequency band. The findings confirm the suitability of the proposed directional coupler structure as a compact and self-packaged solution for high-frequency applications.