Stirred mode reverberation chambers for radio type approval emission measurements

Limits to EIRP set the minimum separation distance for the avoidance of interference, but if this separation cannot be guaranteed an interference probability still exists, and this will be more closely related to the total radiated power. However, measuring total radiated power of some microwave equipment poses a problem in that the antenna port is inaccessible. The stirred mode chamber is one answer. Similarly if the EUT antenna gain is known the method can be used to determine EIRP with less uncertainty than other methods (±1 dB time-averaged field uniformity.) The paper describes a novel method of predicting the error due to unstirred radiation using a ray description. Measurements of the level of unstirred radiation using vector averaging are presented and used to improve the time-averaged field uniformity. Economical and fast methods of determining the uniformity of time-averaged fields are also described, using the duality between spatial movements and changes in wavelength. The advantages of measuring time-averaged (rather than peak) power in terms of measuring time and accuracy are discussed. It is shown both theoretically and experimentally (1-110 GHz) how at high frequencies field uniformity could decrease, and how this effect can be avoided