Folded Empty Substrate Integrated Waveguide With a Robust Transition to Grounded Coplanar Waveguide in the Ku Band

The benefits of empty substrate integrated waveguide (ESIW) are already well-known and contrasted in the literature. Different variations of transitions are available to maximize the power injection in that structure. Besides, several topological variations of the ESIW have also been proposed, such as the ridge ESIW, which enlarges the monomode bandwidth at the cost of higher losses and larger cross-section area. This paper presents a new variation of topology: the folded-ESIW, that halves the width of the original ESIW waveguide and maintains the cross-section area with good performance indexes and a similar bandwidth. A discussion is made about the feasibility of this novel topology and a new transition is presented with a high degree of robustness and a minimum electrical length. To validate and prove this new proposal, a back-to-back prototype has been designed, manufactured and measured, with results so promising that give access to new design strategies in the ESIW field.