MATLAB/Octave function to evaluate time-domain signals according to the measurement bandwidth and average/peak detector of EMI test receivers

Abstract

Electromagnetic emissions are often measured with EMI (electromagnetic emissions) test receivers or spectrum analyzers [1] that must be specifically set up regarding their measurement bandwidth, frequency step size and measurement time (e.g. [2] for automobiles). Additionally, the emissions must be evaluated by different measurement detectors (e.g. average or peak) that may all have individual limit lines like in [2]. EMI measurements can be done in frequency or in time domain [1]. Frequency-domain measurement devices sequentially apply the superheterodyne principle to the frequencies of interest [3]. Since the measurement time for each frequency may take up to several seconds, the total measurement time can become long and cumbersome [4]. To overcome this problem, the time-domain signal can be processed by using, e.g., fast Fourier transforms (FFTs) and further methods [4]. This principle can also be applied to evaluate time-domain simulation results according to EMC standards. There are numerous publications on this topic including, e.g., [4] and [5]. In this contribution, a MATLAB/Octave function is presented that evaluates time-domain signals according to EMC standards. This “virtual EMI test receiver” mimics actual EMI test receivers regarding their measurement bandwidth, frequency step and average/peak detection. Potential use cases include the EMC evaluation of oscilloscope measurements or simulation results. The developed function can be found in the MATLAB Central (https://mathworks.com/matlabcentral/) under the title “Virtual EMI test receiver” by Andreas Bendicks [6]. In the following section, the superheterodyne measurement principle is described that is mimicked by the virtual EMI test receiver. Afterward, the corresponding signal processing of the MATLAB/Octave function is explained. The precision of the MATLAB/Octave function is verified by comparing its results to the ones of an actual EMI test receiver. The work is closed by a conclusion and an outlook.