New Wideband Transition From Microstrip Line to Substrate Integrated Waveguide

Abstract—A new wideband transition from microstrip line to substrate integrated waveguide (SIW) is introduced. Unlike most transitions that show reduced return loss over significant parts of a regular waveguide band, the presented configuration achieves return losses better than 30 dB in standard waveguide frequency bands from X to E. The new aspect of this transition is the addition of two vias to the widely used microstrip taper transition. More-over, the influence of the substrate height is demonstrated. The re-sults in each frequency band are compared with the data for the regularmicrostrip taper alone. A design formula for the placement of the vias and taper dimensions is presented and demonstrated to provide excellent results. The structures are simulated and opti-mized with CST Microwave Studio. Measurements performed on a Ku-band back-to-back prototype transition demonstrate a min-imum return loss of 26.05 dB and maximum insertion loss of 0.821 dB over the entire Ku-band, thus validating the design approach. Index Terms—Microstrip, substrate integrated waveguide (SIW), taper, transition, wideband. I