Improvements to a Method for Estimating the Maximum Radiated Emissions From PCBs With Cables

It has been shown in previous studies that the coupling from ICs, traces, or heatsinks on a printed circuit board to an attached cable can be modeled by placing equivalent common-mode sources between the board and the cable. In a 2008 paper published in the IEEE Transactions on Electromagnetic Compatibility, a closed-form expression was developed to estimate the maximum radiated emissions from board-source-cable structures. While this expression is reasonably accurate for frequencies not exceeding 500 MHz, it may unnecessarily overestimate the emissions in some situations, especially when the maximum frequency of interest is extended beyond 500 MHz. This paper introduces two enhancements to the previously introduced closed-form expression based on improved methods for determining the maximum value of F(θ,k,l ) and the effective board size. The new closed-form expression is evaluated for various board geometries and frequency ranges by comparing the estimated maximum radiated emissions to full-wave simulation results.