A broadband multistate interferometer for impedance measurement

We present a new four-state interferometer for measuring vectorial reflection coefficient from 50 to 1800 MHz. The interferometer is composed of a four-state phase shifter, a double-directional coupler and a spectrum analyzer with an inbuilt tracking generator. We describe a design of the interferometer and a method developed for its calibration. The technique is based on a linear model and a LSQ method accounting for nonlinear constraints that enable to reduce the number of identified system parameters. Experimental data verify good accuracy of the impedance measurement.