I. Introduction
Six-port reflectometers [1], developed as an alternative for vector network analyzers, are more and more often used in contemporary electronics. Due to their high accuracy, simple structure and low power consumption they have found a wide range of application in e.g., displacement and vibration sensing system [2], permittivity measurements [3], or vital sign monitoring [4]. A rapid development of six-port technique has resulted in variety of reflectometers' designs, which differ in the power numbers from the simplest four ports [5] to e.g., ten-ports ensuring better measurement performance [6].