An Estimation Method for EMI Radiated Emissions Using Measured Source Voltages

A method applicable for estimating radiated emissions from printed circuit board traces and connecting cables is proposed. Empirical formulae are derived to predict emission levels in a conventional 10 m semianechoic chamber in the 30-1000 MHz range, which is required for electromagnetic compatibility/electromagnetic interference (EMI) tests in CISPR 32 and EN 55032. The objective of the proposed technique is to facilitate product and component EMI compliance evaluations in the early design stage. Instead of time-consuming measurement processes within the range, estimations can be made in terms of near-field probing results and transformation formulae. According to trace and cable lengths, either long- or short-length mode equations can be employed. Estimations of mock-up and actual circuit boards made with the proposed method were compared with 10 m measurement range results to validate the effectiveness of this approach. Good agreements are observed. This method can be a time-efficient and cost-effective diagnosis tool for products required to pass the EMI compliance test.