Microstrip to Ridge Empty Substrate-Integrated Waveguide Transition for Broadband Microwave Applications

The empty substrate-integrated waveguide (SIW) (ESIW) is an evolution of the SIW. Just as the SIW, the ESIW is of low cost and low profile, and can be integrated into a printed circuit board, but the losses in the ESIW are lower than in those in the SIW thanks to the removal of the dielectric material, which results in ESIW devices with performances close to those implemented with standard rectangular waveguides. In order to increase the operational (monomode) bandwidth of the rectangular waveguides, a metal ridge can be inserted (leading to the ridge waveguide). Extrapolating this idea to the ESIW, in this letter, a study of possible ridge ESIW (RESIW) geometries has been performed, and a novel transition from microstrip line to RESIW is proposed. In order to validate the performance of transition, a back-to-back prototype has been manufactured and measured.