A Method for Complex Impedance Determining by the Reflection Coefficient Magnitude-Only Measurement

A simple but accurate method for determining the complex impedance of an arbitrary load is described. This method does not require the use of a vector network analyzer or phase measurement. Two measurements of the reflection coefficient modulus S11 are carried out for an unknown load. The first measurement is performed for the single load. Then the known active resistance is to be connected in series to the load and the measurement is repeated. By means of Smith chart, it is shown that the load resistance and reactance can be derived from the known value of additional resistance and two values of S11 magnitude. Formulas are given that allow calculating of the complex impedance from the data obtained by measurements. Experimental verification has been carried out that showed the feasibility of the method. The described method could be useful for the realization of matching networks and antenna tuners.