Doppler characteristics of electromagnetic echoes from sinusoidal water waves illuminated by plane wave/Gaussian beam

Abstract

The Doppler spectra of the scattering fields from sinusoidal water waves illuminated by a plane wave or Gaussian beam are numerically simulated with the method of moment (MoM). When the sinusoidal water surface is illuminated by a plane EM wave, the numerical results show that the Doppler spectrum of the scattering field is distorted seriously due to the frequency leakage. For this case, not only the resonance spectral peaks corresponding to the phase velocity of the water wave but also other equally spaced harmonic peaks appear on the spectrum curve. However, when the sinusoidal water surface is illuminated by a Gaussian beam with appropriate beam width, the harmonic peaks can be effectively suppressed. To better explain this phenomenon, the theoretical model for the spectrum of the scattering field from a sinusoidal water wave is derived based on the first-order small slope approximation theory (SSA-I). And this theoretical model proposed by us could give a reasonable explanation for the above phenomenon.