IEC 61726-2015 pdf Cable assemblies, cables, connectors and passive microwave components – Screening attenuation measurement by the reverberation chamber method

For the determination of the screening attenuation, the tracking generator output has to be connected to the DUT instead of the input antenna and the measurement sequence from the first step is repeated. Then the screening attenuation simply can be calculated by subtracting the result from the first step from the one of the second step. This can either be done in a post processing step as well as by using the thru-calibration of modern spectrum analysers with build in tracking generators (therefore the first step is used to calibrate the system). To check the maximum dynamic range, the DUT needs to be replaced by a shielded match load and the second measurement has to be performed with this configuration. If the result is not fulfilling the needs on dynamic range, the resolution bandwidth hast to be reduced. It has to be kept in mind that this might enlarge the measurement time a lot because a reduced measurement bandwidth is coming along with an enlarged sweep time. 7.3 Measurement of the insertion loss of the cavity The synthesized generator is connected to the input antenna and set to deliver a constant power at a fixed frequency. The mode stirrer is also set to rotate at a constant speed. All parameters, i.e. rotation speed and spectrum analyzer set-up (except for input attenuator and reference level) shall be the same as those used during DUT measurement. The spectrum analyser is connected to the output of the reference antenna. After a complete revolution of the mode stirrer, the maximum value of the power is recorded.
7.4.3 Measurement of a calibrator A calibrator is a device having stable screening attenuation. An example of a calibrator is given in Annex B. Such a calibrator should be measured during the full calibration procedure for the test set-up, and compared to previous measurements. This enables the detection of any deviations or malfunctioning of the test set-up. The calibrator is the subject of on-going study to derive its theoretical screening attenuation from Z t and Z f , in order to provide the necessary data for calibration of the test equipment. 7.4.4 Measurement of lossy DUT Some inaccuracy may occur when measuring a lossy DUT, due to insufficient moding of the reverberation chamber. This may be checked by verifying that during one revolution of the mode stirrer, the ratio between the maximum and the minimum power at the output of the reference antenna exceeds 20 dB.