A coaxial-to-microstrip transition for multilayer substrates

Described is a right-angle coaxial-to-microstrip transition suitable for multilayer substrates. Electrically, it transforms the transmission mode from coaxial (TEM) to microstrip (quasi-TEM). Physically, this transformation occurs in two ways. First, strips of the ground plane are incrementally removed from each metal layer. At the same time, the coaxial line is gradually shifted off-center (i.e., made eccentric) toward the microstrip line. The theory supporting the technique is briefly discussed. To demonstrate, a coaxial transition is designed on a six-metal-layer laminate board. Measurements are compared to a conventional coaxial transition design.