Hyo J. Eom

Coherent scattering of a spherical wave from an irregular surface

The scattering of a spherical wave from a rough surface using the Kirchhoff approximation is considered. An expression representing the measured coherent scattering coefficient is derived. It is shown that the sphericity of the wavefront and the antenna pattern can become an important factor in the interpretation of ground-based measurements. The condition under which the coherent scattering-coefficient expression reduces to that corresponding to a plane wave incidence is given. The condition under which the result reduces to the standard image solution is also derived. In general, the consideration of antenna pattern and sphericity is unimportant unless the surface-height standard deviation is small, i.e., unless the coherent scattering component is significant. An application of the derived coherent backscattering coefficient together with the existing incoherent scattering coefficient to interpret measurements from concrete and asphalt surfaces is shown.

Multiple scattering and depolarization by a randomly rough Kirchhoff surface

A matrix approach has been developed to compute bistatic scattering coefficients which include shadowing and multiple scattering effects for a randomly rough Kirchhoff surface. The method permits the computation of these coefficients in terms of the existing single-scatter bistatic scattering coefficients. Thus the effects of multiple scattering are readily recognized from the expressions obtained. The bistatic scattering coefficients are shown to satisfy energy conservation to at least two significant figures. It is observed that while polarized backscattering is dominated by the single-scattering process, the depolarized backscattering is due to multiple scattering. Unlike depolarization by slightly rough surfaces or volume scattering, the angular behavior of the depolarized backscattering is similar to that of the polarized backscattering. The transitional behavior of the relative dominance between single and multiple scattering for the polarized and depolarized scattering coefficient as a function of the azimuth angle is illustrated.

Electromagnetic penetration into a rectangular cavity with multiple rectangular apertures in a conducting plane

Electromagnetic wave penetration into a rectangular cavity with multiple rectangular apertures is studied. The Fourier transform and the mode matching method are used to obtain simultaneous equations for the modal coefficients. The simultaneous equations are solved to represent the cavity field in series forms, which are suitable for numerical computations. Numerical computations are performed to investigate the field penetration into a cavity in terms of the shielding effectiveness for a various geometry.

A theory of wave scattering from an inhomogeneous layer with an irregular interface

Bistatic wave scattering from a layer of Rayleigh scatterers with an irregular interface is investigated by combining the doubling method in volume scattering with the Kirchhoff method in rough surface scattering. Theoretical results are shown illustrating the effect of the rough interface. It is found that for scattered and incident angles near the vertical, the rough interface causes a substantial increase relative to the plane interface in both the like and cross-scattering coefficients over all azimuth angles. However, for large scattered and incident angles, the reverse is true except for azimuth angles around the specular direction. It is interesting to note that while one dominant peak of the like polarized scattering coefficient occurs along the specular direction, two dominant peaks of the cross-polarized scattering coefficient may appear symmetrically with respect to the specular direction. In backscattering, the surface roughness causes a peak to appear in both the like and cross-scattering coefficients at near vertical incidence and also a decrease of these coefficients at large incidence angles.

Analysis of TM scattering from finite rectangular grooves in a conducting plane

TM-wave scattering from rectangular grooves in a perfectly conducting plane is investigated. A Fourier-transform technique is employed to express the scattered field in the spectral domain as a superposition of the parallel-plate waveguide modes. The boundary conditions are enforced on the conducting surface and the groove apertures to obtain simultaneous equations for the transmitted field inside the grooves. The simultaneous equations are solved to obtain the transmitted field in a series representation that reduces to a closed form in a high-frequency scattering regime. With the use of the stationary phase approximation, the far-zone scattered field is obtained, and its scattering behavior is studied in terms of the scattering angle. The diffraction efficiency for the finite grating as the number of grooves increases is presented.

An analysis of transverse electric scattering from a rectangular channel in a conducting plane

The problem of transverse electric plane wave scattering from a rectangular channel which is engraved in a perfect conducting plane is investigated. A Fourier transform technique is employed to express the scattered field in the spectral domain in terms of parallel-plate waveguide modes. The boundary conditions are enforced on the conducting surface and the channel aperture to obtain simultaneous equations for the transmitted field inside the channel. The simultaneous equations are solved to represent the transmitted field in a series form. By using the stationary phase approximation, the exact expression for the far-zone scattered field is obtained and the echo width behavior is numerically studied in terms of the scattering angle, frequency, and channel size. It is found that the behavior of the echo width versus the channel depth exibits resonance irrespective of the size of the channel width. An approximate series expression (Kirchhoff solution) for the echo width is valid for high-frequency scattering regimes (a > 2 λ). We also present an approximate closed form solution for nadir backscattering which is valid when a > 0.2λ.

Radiation of a Leaky Coaxial Cable With Narrow Transverse Slots

The problem of a leaky coaxial cable with narrow transverse slots is solved by using the Fourier transform and mode-matching techniques. The characteristics of far-field radiation and near-field coupling are presented in terms of numerically fast convergent series. Our theoretical results are compared with experimental data to confirm favorable agreement

TE-Plane Wave Scattering from a Dielectric-Loaded Semi-Circular Trough in a Conducting Plane

The theoretical behavior of TE-plane wave scattering from a dielectric-loaded semicircular trough in a conducting half-space is investigated. The dielectric loading is made of a circular cylinder which is partially buried in a semi-circular trough in a perfectly conducting plane. The scattered field is numerically evaluated to investigate the angular scattering pattern under the various dielectric loading conditions. The presence of the dielectric loading in the trough can substantially affect the angular scattering behavior. The difference between the TE and TM-scattering angular patterns is also observed. The field magnitude inside the trough is found to be much greater than the outside, thus indicating that the trough focuses the incident beam inside the trough.

Acoustic scattering from a rectangular aperture in a thick hard screen

Acoustic scattering from a rectangular aperture in a thick hard screen is examined. The Fourier transform is used to represent the scattered wave in the spectral domain and the boundary conditions are enforced to represent a solution in closed form. Numerical computations are performed to illustrate the behavior of the scattered wave from a thick rectangular aperture. The solution is represented in series which are numerically efficient.

TM scattering from a slit in a thick conducting screen: revisited

TM plane wave scattering from a slit in a thick conducting screen is examined. A Fourier transform technique is employed to express the scattered field in the spectral domain and the boundary conditions are enforced to obtain simultaneous equations for the transmitted field inside the thick conducting screen. The simultaneous equations are solved to represent the transmitted and scattered fields in series forms. Approximate series solutions for scattering and transmission are obtained in closed-forms which are valid for high-frequency scattering regime. >