Effects of the Variation of the Excitation and Boundary Conditions of Mode-Stirred Chambers and Consequences for Calibration and Measurements

Field transients are an intrinsic feature of mode-stirred chambers. Three different cases are investigated here. The free energy decay corresponds to transients on a microsecond time scale. The time for transients due to a change of frequency depends on the equipment used. In any case it is significantly longer, usually several milliseconds. If a mechanical tuner is used to change the boundary conditions, due to the inertia of the construction, transients occur within a time period up to several seconds whenever the tuner is moved to a new position. All these field transients may affect equipment under test. Moreover, the free energy decay can be used to determine the chamber quality factor in the time domain. For this task, a method, using a spectrum analyzer instead of an oscilloscope, is introduced leading to a much higher dynamic range.