Wideband Transition for Increased-Height Empty Substrate Integrated Waveguide

Recently, Empty Substrate Integrated Waveguide (ESIW) technology was proposed for embedding empty waveguides into planar substrates in order to improve their performance. A low-loss and narrow-band transition from microstrip to an increased height ESIW with 4 layers was presented in a previous work, and used to implement a very high-quality factor bandpass filter at Q-band. With such a narrow-band transition, based on a quarter-wavelength transformer, a very narrow-band filter response with resonators having a quality factor of 1000 was achieved. In this paper, in order to overcome the narrow-band and the 4-layers output restrictions, and extend the practical use of such increased height ESIWs beyond narrow-band filters, we present a novel wideband transition from microstrip to an increased height ESIW with an arbitrary number of layers. A full suite of wideband transitions to increased height ESIWs, built with different number of substrate layers ranging from 3 to 8, has been designed in this work to operate at Ka-band, though they can be easily transferred to other bands if the dimensions of the transition are properly scaled. To illustrate this, the original Ka-band transitions have been mapped to Ku-band, with excellent results. In order to test the proposed design method, a prototype of a 4-layer structure has been fabricated at Ka-band, achieving a good performance in the whole useful bandwidth of the ESIW.