A coaxial to differential adapter

Virtually all RF test and measurement instruments employ single-ended coaxial interfaces, even when they are designed for making differential measurements. Transition from coaxial to differential signal transmission potentially causes disruption in the differential impedance, resulting in reflections that distort the measurement being made. To facilitate connection to a variety of differential laboratory fixtures, an adapter was designed to transition the connection of standard coaxial 3.5 mm interfaces to a hermaphroditic differential interface. Since the adapter has one each pin and socket coaxial inputs, a mated pair of adapters provides an insertable device for test on a four port VNA. Four-port and mixed mode S-parameter as well as time domain reflectometer data for the adapter are presented. Challenges involved in the design of the adapter are discussed. Potential for a native differential TRL calibration is explored.