Port crosstalk effects in six-port modulator

Most of the articles focusing on six-port modulators deal with ideal scattering parameters, where the reflections of all ports are considered as zero and the isolations between modulation ports are infinite. When this assumption is used, the ideal transfer function is depending only on reflection parameters of connected impedances, s-parameters between input and modulation ports and also between modulation and output ports. In case of six-port modulator analysis with non-idealized parameters, which are typical e.g. for SIW technology based on cheap substrates, where these isolations between modulation ports can be in the range from 10 to 20 dB, the high transfer function errors occur. Due to this fact, it is necessary to find other strongly affecting paths between input and output and also to include the paths with more than one reflection. This paper will present results and differences of the transfer function by application of commonly used fundamental paths and solution with extended paths for several combinations of modulation impedances. The transmission parameters of the modulator will be also compared with the results of the model solved in Ansoft Designer®.