Design features of multi-port reflectometers

Abstract

Guidelines are developed, based on least-error criteria, for the design of reflectometers working on the 6-port power measurement principles. A general matrix analysis is established which yields solutions for all designs of coupler. In particular, it is shown that it is not necessary to single out a special port for determining the reference power, provided that the coupler is designed with an appropriate form. One such ideal design without a reference port is discussed. The performance of the ideal couplers are related to realisable couplers through modified reflection coefficients and modified scattering matrices. These transformations from the realisable to the ideal help in the understanding of practical systems and their design. Finally, a 10-port reflectometer is described, where the extra information is used to either extend the dynamic range or to increase the level of accuracy. The system, with an extended dynamic range, could measure |ρ| > 1 as well as |ρ| ≤ 1, and so find particular use in the measurement of active systems as well as passive devices.