Reappraisal of computer-corrected network analyser design and calibration

Abstract

A rigorous analysis is carried out of a typical dual-directional coupler network analyser to demonstrate the application of a new circuit analysis technique based on the principle of matrix renormalisation, described in a companion paper, to cascaded multiport networks. The manner in which previously published calibration equations were derived is explained in detail. The analysis is carried out external to the network in terms of voltage excitation and the voltage responses at the accessible ports of the network under mismatched conditions. Each section of the network is represented by a generalised scattering matrix defined in terms of voltage-wave S-parameters with complex normalisation. In this manner, a knowledge of the internal flow paths of the network is unnecessary, in contrast to the flowgraph method employing the nontouching loop rule. The analysis shows that current methods of network analysis, based on the power-flow concept, have given rise to certain misconceptions because source mismatch does not contribute to systematic error-as is generally believed. In addition, these misconceptions appear to have led to the adoption of general design principles for network analysers that are unnecessarily complicated because the effects of mismatches, discontinuities and poor directivity can be completely eliminated by calibration in terms of air-dielectric line standards, provided that all port mismatches are invariant between the reflection and transmission modes of operation.