Physics and Overview of Electromagnetic Scattering

Physics and Overview of Electromagnetic Scattering

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This chapter has presented an overview of electromagnetic scattering. We have seen that RCS is a measure of power scattered from the incident wave; that it is a function of the angular orientation and shape of the scattering body, frequency, and polarization of the transmitter and receiver. The scattered wave, of which RCS is a measure, is caused by reradiation of currents induced on the scattering body by the incident wave. The scattering process breaks into three natural regimes: the low-frequency or Rayleigh region, where the wavelength is much longer than the scattering body size and the scattering process is due to induced dipole moments where only gross size and shape of the body are of importance; the resonant region, where the wavelength is on the same order as the body size and the scattering process is due to surface waves (traveling, creeping, and edge) and optics; and the high-frequency optics region, where the wavelength is much smaller than the body and the scattering process is principally a summation of the returns from isolated, noninteracting scattering centers. Maxwell's equations tell us that EM waves are a combination of electric and magnetic fields that are perpendicular to each other and to the direction of propagation. When an EM wave is incident on a body, the boundary conditions on the fields require that surface currents flow. These currents, in turn, reradiate a scattered EM wave. The strengths of the reflected and transmitted waves for specular scattering are given by the Fresnel coefficients, which are functions of the incident polarization and material properties. Surface fields were shown to be characterized as surface electric and magnetic currents and charges. The formal expressions that then relate the surface source currents and charges to the scattered fields are then known as the Stratton-Chu equations, which are an alternate expression of Maxwell's equations. These expressions are integrals of source currents and charges over the scattering body.

Chapter Contents:

  • 3.1 Introduction
  • 3.2 Radar Cross Section Definition
  • 3.2.1 IEEE RCS Definition
  • 3.2.2 Intuitive Derivation for Scattering Cross Section
  • 3.2.3 Other Cross-Section Concepts
  • 3.2.4 Polarization Scattering Matrix
  • 3.3 Fundamental Scattering Mechanisms
  • 3.3.1 Electromagnetic Wave Fundamentals
  • 3.3.2 The Scattering Process
  • 3.4 Scattering Regimes
  • 3.4.1 Low-Frequency Scattering
  • 3.4.2 Resonant Region Scattering
  • 3.4.3 High-Frequency Optics Region
  • 3.5 Electromagnetic Theory
  • 3.5.1 Source Quantities for Fields and Maxwell's Equations
  • 3.5.2 Electromagnetic Scalar and Vector Potentials
  • 3.5.3 Wave Equation
  • 3.5.4 Waves at Boundaries
  • 3.5.5 Reflection Coefficients
  • 3.5.6 Wave Reflection from Surface Current Point of View
  • 3.5.7 Stratton-Chu Equations for the Scattered Field
  • 3.6 Summary
  • References
  • Select Bibliography

Inspec keywords: electromagnetic wave scattering; Maxwell equations; electric fields; magnetic fields; electromagnetic wave polarisation; electromagnetic wave propagation

Other keywords: boundary conditions; RCS; incident polarization; material properties; creeping waves; low-frequency region; electric fields; edge waves; noninteracting scattering centers; surface electric currents; induced dipole moments; traveling waves; surface charges; surface waves; Stratton-Chu equations; incident wave; Maxwell equations; scattering body size; surface source currents; surface magnetic currents; EM waves; Rayleigh region; resonant region; electromagnetic scattering; shape function; angular orientation; magnetic fields; high-frequency optics region; propagation direction; induced current reradiation; Fresnel coefficients

Subjects: Electromagnetic wave propagation; Magnetostatics; Electromagnetic waves: theory

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