Return Path Discontinuity Analysis of an Edge Mount SMA Launch Structure in Multilayer Boards

Return-path discontinuity of an edge-mount SubMiniature version A (SMA) launch structure in multilayer boards, widely used in high-frequency fixtures and boards, is analyzed, and a simple equation to quantitatively estimate the frequency bandwidth without signal distortions is proposed. The proposed equations are experimentally validated for various physical dimensions, and a simple circuit model is demonstrated to take the return-path discontinuity into account in the channel simulations. In addition, based on the understanding of the return current discontinuity, quantitative design guides are drawn and a technique using an edge plating to enhance the bandwidth up to 50 GHz is demonstrated.