Ultra-Wideband Microstrip to Substrate Integrated Waveguide (SIW) Vertical Transition

an ultra-wideband vertical microstrip to substrate integrated waveguide (SIW) transitions is proposed for Three-dimensional (3-D) densification. The corner formed by the two different transmissions lines and electrical walls can easily transform the E-field of the dominant mode in the microstrip line to the SIW mode. An equivalent model based on the lumped element is proposed to estimate the initial parameters and to study the performances of the structure. Based on this model, two configurations are built. In the first configuration, the SIW line is on the same side of the microstrip line (MSL) and in the second one, it is integrated into the side of the ground plane. For experimental validation, two back-to-back prototypes MSL-SIW-MSL transitions are fabricated, with a SIW line acting as a bridge. The measured results agree well with those in the simulations, showing a return loss better than 10 dB over the entire 22 - 50 GHz frequency range with a maximum insertion loss of 1.8 dB.