Redefinition of the Amplitude Probability Distribution Measuring Function for Electromagnetic Emissions Assessment

The amplitude probability distribution (APD) is a measuring function for assessing electromagnetic disturbances, especially those with a stochastic and time-varying distribution. According to the CISPR 16-1-1, the APD has been defined as the cumulative distribution of the probability of time that the amplitude of disturbance exceeds a specified level. The APD is highly correlated to the bit error rate of digital communication systems, and therefore, a redefinition of radiated emission limits based on the APD would be very meaningful in terms of protecting wireless systems from unintentional interferences. However, establishing emissions requirements based on the current standard APD method can be misleading and not completely traceable metrology-wise. This is because, when analyzing electromagnetic compatibility (EMC) standards, the current specifications for APD measurements are unclear and ill-posed. For instance, the APD is only defined for applications above 1 GHz and with a fixed resolution bandwidth of 1 MHz; both conditions are arbitrarily set due to legacy considerations. Given the capabilities and flexibility of available instrumentation technology, we will propose an improved and more general APD definition accompanied by a calculation algorithm. Moreover, we argue that the APD measurements shall move from a histogram-based approach and implement kernel density estimation instead. We deliver evidence that exemplifies and supports our revised APD definition through numerical simulations. The study closes with a critical discussion about why the APD is so relevant and how it can be redefined to become widely employed as part of EMC assessments.