A novel transition from microstrip to a substrate integrated waveguide with higher characteristic impedance

Microstrip tapered transitions are commonly used as the best solution when an interface between substrate integrated waveguide (SIW) and a microstrip line is needed. However, in this paper, we show how the microstrip taper works much worse when the SIW has a high characteristic impedance compared to the microstrip one, and how a transition made in SIW has better performance in this case. Field plots, full-wave simulations and measurements validate the proposed solution for that case. Analytical equations for positioning the via holes forming the transition are obtained and tested with two examples.