Reflection-type Q factor measurement of transmission-type cavities

The traditional method of measuring the unloaded Q factor of a transmission cavity is the so-called insertion-loss method. The accuracy of that method deteriorates when the coupling becomes strong and when the input and output coupling coefficients differ from each other. To circumvent these difficulties, it is proposed to terminate one of the cavity ports with a matched load and measure the Q factor of the other port by the reflection-type method. The ports are then exchanged, and the measurement repeated from the other side. Such measurement provides an estimate of the uncertainty of the unloaded Q factor, and also works well when the input and output coupling coefficients differ from each other.