SIW-to-Mini-Coaxial Vertical Transition for Low Profile MM-Wave PCB-to-PCB Assembly

A vertical transition between substrate integrated waveguide (SIW) and super mini-coaxial connector for millimeter-wave (mm-wave) is presented. It consists of via-pad/anti-pad structure embedded in the SIW printed circuit board (PCB) to match the SIW's TE₁₀-like mode and the connector's TEM mode with low loss over the operating frequency band. The transition is designed and used to construct back-to-back test structures at 20 GHz and 30 GHz bands for evaluation. Both the simulation and measurement results are presented.

I. Introduction

Substrate integrated waveguide (SIW) structure offers ease fabrication while sharing comparable electrical performance with metallic rectangular waveguide, such as high power capability, low insertion loss, low interference, and efficient integration to planar and non-planar circuits [1], [2]. Due to their compatibility to PCB multi-layer fabrication and assembly, SIW vertical transition to other front-end RF circuits and antennas are preferred. In SIW to coaxial-probe transition, the coaxial probe has to penetrate through the SIW substrate and be shorted to the SIW’s ground plane which impacts the transition performance [3], [4]. Also, the size of regular coaxial connector becomes an issue when testing SIW components at mm-wave band and it would make the whole integrated system high profile.