The ridge gap waveguide as a wideband rectangular hard waveguide

The present paper will give an overview of the research on hard surfaces and hard waveguides leading to the wideband ridge gap waveguide. The overview will be supported by both computed and measured results of the performance of hard waveguides and gap waveguides, clearly showing the wide bandwidth and low losses of the latter. This is a major improvement compared to the original hard waveguides, enabled by the wideband parallel-plate cut-off fenomena used for the gap waveguides.