Precision microwave attenuation measurement by time interval ratio

A method of measuring microwave attenuation by substitution is described. As attenuation is inserted into the device under test, the pulse repetition frequency of a pulse modulated PIN diode switch in series with the device is changed to maintain a constant mean power output from the circuit. The ratio of the pulse repetition frequencies before and after insertion is shown to be simply related to the attenuation of the device under test. Error sources are examined. Results show inaccuracies + or 0.002 dB over a range of 0 to 20 dB.