Stirred mode reverberation chambers for EMC emission measurements and radio type approvals or organised chaos

Limits to the EIRP set the minimum separation distance for the avoidance of interference, but if this separation cannot be guaranteed a probability of interference still exists, and will be more closely related to the total radiated power. However measuring the total radiated power of microwave integrated equipment poses a problem to which the stirred mode chamber (SMC) holds an answer. Similarly if the equipment under test (EUT) antenna gain is known the method can be used to determine the 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 decreases, and how this effect can be avoided