A Wideband Microstrip Line to Empty Substrate Integrated Waveguide (ESIW) Transition

The empty substrate integrated waveguide (ESIW) is a popular technology that has gained widespread attention in the past decade. It is basically a substrate integrated waveguide with no dielectric that have minimal losses along the direction of wave propagation. This article presents an improved microstrip to empty SIW (ESIW) transition, aiming to alleviate fabrication complexity with enhanced performance characteristics. The transition includes a microstrip line, a tapered region, and a $\lambda $ /4 long stepped structure protruding into the ESIW. The taper region eliminates discontinuity effects and ensures good impedance matching. While, the stepped profile offers ease of design and manufacturing compared to previously reported transitions. The back-to-back Transition I is designed, fabricated and its characteristics are measured. The fabricated Transition I offers a fractional bandwidth (FBW) of 77.40% for a frequency range of 7.6–17.2 GHz (X and Ku band) with return loss (RL) and insertion loss (IL) better than 14.4 and 1.5 dB, respectively. In order to validate its usability at higher frequency bands, Transition II is designed for K/Ka band applications. It offers a FBW of 70% for a frequency range of 18.9–39.3 GHz (K/Ka band) with RL and IL better than 20 and 1.5 dB, respectively.