Reciprocity in EMI-EMC

The basis of and errors in interpreting the law of reciprocity are reviewed and applied to conducted and radiated electromagnetic interference-electromagnetic compatibility (EMI-EMC). Conditions for reciprocity include reversibility and passivity of elements in the reciprocal system. The law is expressed in circuit form and the reciprocal signals are clearly distinguished. Symmetric and asymmetric line filters are used as examples of reciprocity in conducted interference. It is shown that an incompletely shielded circuit can be regarded as an antenna, allowing one to establish radiation reciprocity between it and a measuring antenna. Some difficulties encountered in EMI-EMC measurements that give the impression of reciprocity being violated are discussed. >