Integration of a Very High Quality Factor Filter in Empty Substrate-Integrated Waveguide at $Q$ -Band

Recently, new methodologies for manufacturing empty waveguides completely integrated in a planar substrate have been proposed in order to improve the performance of substrate-integrated devices. One of these alternatives is the so-called empty substrate-integrated waveguide (ESIW). The height of high-frequency substrates, where ESIW devices are integrated, is very small. Then, the capacity of storing energy of ESIW resonators is drastically reduced, and as a result, their quality factor is not as high as it could be with a higher ESIW. In order to overcome this restriction, a novel integrated structure is proposed to embed very high-quality factor filters based on the ESIW with an increased height. As a result, we show, in this letter, for the first time, the successful integration of an increased-height ESIW filter in a printed circuit board of 0.305 mm height at $Q$ -band, achieving a quality factor above 1000, which is a remarkable result for a completely substrate-integrated device operating in this frequency band. When compared with the same filter manufactured with an ESIW with the same height as the substrate, the novel filter shows a measured quality factor 85% higher.