An improved broadband transition between microstrip and empty substrate integrated waveguide

In this letter, an improved broadband transition between microstrip and empty substrate integrated waveguide (ESIW) is proposed. The transition structure consists of a gradient microstrip line, a taper extended into ESIW, and ESIW section. Compared with the previous studies, the gradient microstrip line is introduced to expand the operating bandwidth and get a better performance, especially for the thinner dielectric substrate. The simulated and measured results have a good agreement. A back‐to‐back transition is designed, manufactured, and tested. For a single transition, the return loss and insertion loss are better than 13.5 and 0.75 dB from 6.6 to 16.45 GHz (85.5%), respectively.