Probabilistic Approach to Defining Emission Limits in Terms of Total Radiated Power

A method of defining emission limits in terms of total radiated disturbance power is presented, which is effective for testing mobile and portable devices. The radiated power from equipment under test can be measured in a reverberation chamber (RC), which is an attractive alternative to a fully anechoic room (FAR) because of its space factor, cost effectiveness, and higher measurement sensitivity. Usually, the radiated power measured in RC is converted to the maximum field strength and compared with the relevant limit in tests in FAR. This conversion needs an assumption on the unknown maximum directivity of disturbance radiation, which is a major cause of uncertainty. The approach presented here enables us to derive a radiated power limit without knowing the maximum directivity of radiation. Disturbance radiation with high directivity generally increases the maximum field strength at the radio receiver being interfered, but at the same time, it decreases the probability that the maximum directivity is in the direction of the receiver. The limit derivation is based on the principle that the effects of the above two factors on the probability of interference cancel each other when the source device meets certain conditions.