Articles | Volume 14
https://doi.org/10.5194/ars-14-147-2016
https://doi.org/10.5194/ars-14-147-2016
28 Sep 2016
 | 28 Sep 2016

A near-field measurement based method for predicting field emissions below 30 MHz in a CISPR-25 test set-up

Zongyi Chen and Stephan Frei

Abstract. Automotive electric components are required to pass radiated emission tests. According to CISPR-25 standard (ALSE method), an expensive anechoic chamber is needed for conducting the field emission testing. Reproducibility due to high sensitivity to chamber and setup details is poor. Alternative methods, which perform measurements without using a chamber are preferred. This paper provides an alternative pre-compliance method for predicting the fields of CISPR-25 results for frequencies below 30 MHz, based mainly on electric near-field measurements. The motivation is that common-mode current measurements or magnetic near-field measurement based methods give good field prediction above 30 MHz, but fail below 30 MHz. The proposed method applies Huygens' Principle for field prediction. The electric field distribution for the defined Huygens' surface and the equivalent currents are estimated from a small number of field measurements close to the ground plane. It is shown that the electric field can be well predicted, compared with a full-wave simulation the deviation is within 4 dB, compared with a standard antenna measurement up to 3 MHz the deviation is less than 1 dB.

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Short summary
A near-field measurement based pre-compliance method is provided for predicting emission below 30 MHz in a CISPR-25 test set-up. The Huygens principle by defining an unclosed Huygens' surface is applied for field prediction. Near-field measurements are only conducted for several locations over a table surface and a static electric field formula is used for field distribution estimation. The difference of the predicted E-field at 1 m distance is within 4 dB compared with full-wave simulation.