Modeling resonance effects in the radiated emissions from a nonlinear system

Resonances in the spectrum of radiated emissions from an electronic device are generally caused by the broadband excitation of underdamped transmission systems; hence, the shape of the spectrum varies with the load and source impedances of the circuits. Such resonances are straightforward to model in a linear system, but the source and load devices in a digital system are highly nonlinear in order to provide rapid and unambiguous switching. The work described in this paper adapts a harmonic balance algorithm for application to the indefinite admittance matrix produced by a partial-element equivalent circuit (PEEC) formulation. The resulting simulation program incorporates a nodal suppression technique to increase efficiency and is used to demonstrate the power dependent shift in the Q of the resonance of a transmission line terminated with a nonlinear load and its effect on the spectrum of the radiated emissions.