Predicting the Radiated Emissions of Automotive Systems According to CISPR 25 Using Current Scan Methods

TLDR: In this article, the authors present a field prediction method, which combines a measured CM current distribution with numerical computations for the radiated fields in the frequency range of 30-1000 MHz.

Abstract: According to automotive standard CISPR 25, electronic components or modules are required to be connected to a specific test cable bundle in order to evaluate the radiated emissions. In the absorber-lined shielded enclosure (ALSE) method, also called the antenna method, the cable bundle is often the dominant radiation structure due to its length. This measurement method requires a large anechoic chamber, but often, it is only the impact of the test cable bundle's common-mode (CM) current distribution that is measured. Since the current distribution can be measured easily with current clamps, and with much lower demands to the environment, it is advantageous that the level of radiated fields can be estimated from the measured current distribution. This paper presents a field prediction method, which combines a measured CM current distribution with numerical computations for the radiated fields in the frequency range of 30–1000 MHz. Applicability is discussed based on several complex test cases. Three major problems had to be solved. First, appropriate current phase measurement methods had to be developed since the current amplitudes are not sufficient for estimating the electric fields. Second, a CM radiation model of a cable bundle had to be found. Third, in order to get comparable data for the ALSE test environment, a method had to be developed that could take this influence into account. Different solution approaches are examined here for the problems mentioned above.