Bandwidth improvement technique for an edge mount SMA launch structure in multilayer boards

A technique to improve the bandwidth of an edge mount SMA launch structure in multilayer boards is proposed. The edge mount SMA launch structure is widely used in fixtures and calibration boards for high-speed serial links, but can suffer from return-path discontinuities in multilayer boards, resulting in bandwidth limitation. The discontinuities in the edge mount SMA launch structure deteriorate the signal transmission quality at high frequencies. An edge mount SMA launch structure is investigated based on a waveguide analysis and relevant analytical equation. In addition, a simple method to mitigate the discontinuity due to the wave propagation into the waveguide structures formed by the multiple return planes in a multilayer board is proposed by using an edge plating technique and validated through numerical simulations.