A procedure to evaluate the output VSWR of high power amplifiers

In this paper a procedure for evaluating the output VSWR of high power amplifiers is introduced and discussed. Essentially, the procedure is based on the comparison between readings of the forward power measured on a directional coupler in different conditions (short circuit and matched load). The error induced by the nonideal directivity of the directional coupler is evaluated and requirements on the minimum directivity necessary for evaluating a VSWR better that 2.0:1 are shown. Some experimental results are shown, regarding the comparison between two commercial amplifiers with relatively low power (50 W, 10 kHz-1 GHz)