Multiport network measurement using a three-port VNA

S-matrix reconstruction transforms are widely used in measurements of multiport devices using a two-port vector network analyzer, especially for noncoaxial applications because high-quality matched loads are hardly accessible. For noncoaxial measurements, strongly reflecting termination, such as a short-circuited or an open-circuited transmission line is more repeatable, reliable and economical than terminations with loss like resistors. Accordingly, the numerical instability associated with strongly reflecting auxiliary terminations is of concern to noncoaxial applications. In this paper, a technique that allows a three-port vector network analyzer to measure multiport devices using strongly reflecting auxiliary terminations is developed to ease the noncoaxial measurements. As demonstrated in Section III, the technique eradicates the numerical instability associated with strongly reflecting auxiliary terminations, and results in an accurate reconstruction of the multiport S-matrix.