First-order theory of the five-port symmetrical star junction

It is shown that, from the three conditions of (a) five-fold symmetry, (b) reciprocity and (c) freedom from loss, useful constraints can be found on the elements of the scattering matrix of a symmetrical five-port star junction. These constraints can be used to set limits to the possible positions qi, of the centres of the q-circles when the five-port junction is used as an element in a six-port reflectometer.