Can we calibrate a 1 mW @ 50 MHz power reference SWR using a VNA?

Abstract

This paper evaluates a process to use a VNA to measure the SWR of a 50 MHz power reference output found in most power meters. Normally measuring this parameter involves the use of a thermistor mount, a power meter, and a more or less complex method that involves in a first step measure the output with the power meter set to the normal bridge setting of 200 ohm and then change it to 100 ohm. The SWR can then be determined, by calculating the mismatch of these two different load conditions. However, if you don’t have a thermistor mount or they are out for calibration is it possible to use a VNA to make the same measurement accurately? Using the VNA and setting up a sweep around the 50 MHz output signal we can measure the SWR in immediate vicinity of the 50 MHz signal. This creates a possible alternate method for measuring the SWR of the reference output using the VNA. We will compare results using the traditional method and the VNA method to find if the VNA method is an acceptable alternative solution.