MICROWAVE NINE-PORT NETWORK ANALYSER

Abstract

It is known that the dual six-port arrangement introduced by Hoer in 1972 provides a more economical alternative to the commercial automatic network analyser for the measurement of the complex scattering coefficients of two-port microwave devices. A novel technique based on an extension of the six-port technique has been demonstrated to be capable of achieving the same objectives. This theory reduces the requisite number of power detectors to six and requires the measurements to be performed at only two operating states of the instrument (as compared with eight power detectors and three instrument states for the dual six-port network analyser). In principle, the proposed technique is applicable to any hardware implementation of the nine-port network. For the present project, six arrangements (each comprising two symmetrical five-port waveguide junctions, a 3 dB and 10 dB directional couplers and a phase shifter) have been studied. A series of Monte Carlo simulations has been conducted to evaluate the robustness of each nine-port system to hardware imperfections. Simulation results reveal that all the six configurations are more sensitive to the residual mismatches in the symmetrical five-port junctions than in the power detectors, hence emphasising the importance of selecting well-matched symmetrical five-port junctions for the proposed application. All six configurations perform equally well when the constituent components are ideal; however, when imperfections are present, the simulation results show that different levels of deterioration in performance can be expected for the various configurations. In particular, two of these configurations are observed to be less sensitive to these imperfections as compared to the others. This shows that an improvement in system design can be effected rather simply by re-arranging the internal connections within the system (instead of by insisting on more stringent design specifications for the constituent components). Finally, laboratory tests on the prototype nine-port system have confirmed that it can measure both reciprocal and non-reciprocal devices, and good measurement accuracies for both the magnitudes as well as the phases for all the four scattering coefficients of the two-port devices can readily be achieved.