Analysis of the radiation from a pigtail-terminated coaxial cable using the imbalance difference model

A simple and quick model is explored to analyze the radiation of the pigtail-terminated coaxial cable in this paper. Unexpected radiated electromagnetic interference is produced due to the pigtail and influences the surrounding equipment. To study the mechanism of the pigtail effect, the actual pigtail connection is modeled as two transmission lines cascade connection. The currents on the transmission lines can be decomposed into differential and common mode currents. Based on the concept of imbalance difference factor, the differential-mode currents are converted to common-mode currents and a common mode voltage source is generated where the imbalance factors of the adjacent transmission lines change. So the common currents and the corresponding radiation are easily achieved. In addition, to improve the accuracy of the result around resonant frequency, the radiation loss of the common mode is considered. A method of how to estimate the radiation loss is proposed. The radiation loss is equivalent to the impedance of the antenna and is added into the differential mode. To validate the derived model, the calculation of the radiation emission is carried out using full-wave simulation and imbalance difference model. A good agreement is achieved.