An alternative method for measurement of radiated emissions according to CISPR 25

摘要

Current scanning methods could be a promising alternative to reduce the need of automotive CISPR 25 ALSE measurements. It is assumed that, especially in low frequency range, the cable bundle is often the dominant radiating structure. Knowing the current distribution along the cable bundle the field at any point can be calculated. First implementation calculated the phase through measured current amplitude, which may produce the error in low frequency range. In order to compensate the mentioned problem, this paper proposes two alternative enhancements of the common-mode current scan methods in time domain for cable bundles. A time domain scan can provide the amplitude and phase information of currents simultaneously through Fast Fourier Transform (FFT). One method, considering the common-mode current as radiation source, models the cable bundle by a set of elementary dipoles to calculate the field emissions. While the other method only uses common-mode current and transmission line parameters at beginning and end ports of cable bundle to calculate the field emissions. Till now an ideal environment was assumed and the complexity of a real ALSE was neglected. In order to improve the prediction quality, a calibration approach based on measured data is proposed, which incorporates real influence factors in an anechoic shielded chamber. Through the verifications by numerical analysis of different cable bundle models and measurements, the stability and feasibility of the mentioned improvements could be shown.