Circuit-concept approach to radiated emissions of printed circuit boards

A radiation circuit model, based on the traditional transmission-line model but considering the effect of finite-size ground trace, is presented for estimating the electromagnetic interference of a typical PCB geometry, namely microstrip. The ground trace is commonly thought of as a low-impedance path for returning currents and one that is of constant potential across its area. In fact, the finite-size ground trace of a PCB is similar to an imperfect ground, the inductive reactance of which is significant. Wire antennas model the common-mode radiation sources caused by an imperfect ground, and superposition and odd-mode/even-mode methods analyse the circuit. The quantitative values of induced current distribution along the conductor traces are addressed thoroughly. Measured data are presented to confirm the results of numerical computations.