THE ELECTROMAGNETIC SCATTERING OF BROAD BANDWIDTH RANDOM SIGNALS BY A DISCRETE TARGET.
Physical sciences research papers no. 345,
AIR FORCE CAMBRIDGE RESEARCH LABS L G HANSCOM FIELD MASS
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Recent papers have emphasized the linear systems aspect of the electromagnetic scattering from a stationary, discrete target. They show that the temporal response of the far-zone scattered field is the convolution of the temporal impulse response of the scatterer with the waveform of the illuminating plane wave. In this paper the scattering system response to an illuminating waveform which is a broadband, temporally stationary random process is discussed. As expected from the classical theory of the noise response of linear systems, the crosscorrelation properties of arbitrary components of the scattered field at two space-time points can be determined from the temporal autocorrelation function of the illuminating waveform and the appropriate target impulse responses. A consideration of the power spectral density of the bistatic scattered field at a large range r from the target leads to an alternate interpretation of the target scattering cross section. It may be thought of as 4 pi r square times the power spectral density of the bistatic scattered field when the target illumination is white noise. By analogy with the classical definition of the bistatic scattering cross section for monochromatic excitation, one can define the effective scattering cross section of a target for broadband illumination. The effective cross section is proportional to the integral over all frequencies of the classical cross section weighted by the power spectral density of the illumination. The effective bistatic cross sections of various targets in the Rayleigh and optics regions are exhibited and compared with the classical bistatic cross sections. Author
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