Finite difference time-domain calculation of transients in antennas with nonlinear loads

Transient currents for an antenna with a nonlinear load are calculated using finite-difference-time-domain (FDTD) methods. The FDTD electric field across the nonlinear load (which determines the voltage across the load) is calculated by solving a nonlinear equation at each time step. This allows the time step to be at the Courant limit, and is more efficient than reducing the time step size in all the FDTD cells to maintain stability in just the cell containing the nonlinear load. The stability of this approach relative to a simpler approach of approximating the diode as a variable resistor is demonstrated. As a validation of the method the transient current in a long dipole antenna with a nonlinear load excited by a pulsed plane wave is computed and compared with calculated results obtained by another method. The approach given here extends the applicability of the FDTD method to problems involving radiation and scattering from antennas including nonlinear loads.>