Anthony A. Triolo

A transport theory of pulse propagation in a strongly forward scattering random medium

The scalar time-dependent equation of radiative transfer is used to develop a theory of pulse propagation in a discrete random medium whose scatter function (phase function) consists of a strong, narrow forward lobe superimposed over an isotropic background. The situation analyzed is that of a periodic sequence of plane-wave pulses, incident from an air half-space, that impinges normally upon the planar boundary surface of a random medium half-space; the medium consists of a random distribution of particles that scatter (and absorb) radiation in accordance with the aforementioned phase function. After splitting the specific intensity into the reduced incident and diffuse intensities, the solution of the transport equation in the random medium half-space is obtained by expanding the angular dependence of both the scatter function and the diffuse intensity in terms of Legendre polynomials, and by using a point matching procedure to satisfy the boundary condition that the forward travelling diffuse intensity be zero at the interface. Curves of received power show that, at small penetration depths, the coherent (reduced incident) intensity dominates, whereas at large depths, the incoherent (diffuse) intensity is the strongest and causes the pulses to broaden and distort. The motivation for this study was to complement a test series, on mm-wave pulse propagation in vegetation, by a theory that provides understanding of overall trends and assistance in the interpretation of measured results. In the mm-wave region, all scatter objects in a forest have large dimensions compared to a wavelength and, therefore, produce strong forward scattering and a phase function of the type assumed in this paper.

An approximate but accurate analysis of the dielectric wedge antenna fed by a slab waveguide using the local mode theory and Schelkunoff equivalence principle

A computationally efficient method to obtain design parameters for tapered radiators is presented. The method uses a local mode theory in conjunction with the Schelkunoff equivalence principle. Radiation patterns of directive gain for dielectric wedge antennas of varying lengths and different dielectric constants are presented. Both the TE and TM cases are considered. The method is validated by comparison with data obtained from a recently developed more rigorous mode-matching method. Excellent agreement is obtained over the physically important angular range from endfire to broadside for the TE case and over the angular range spanned by the major lobe for the TM case.

New full-wave theory for scattering from rough metal surfaces—the correction current method: the TE-polarization case

A new full-wave theory of scattering from metal surfaces with one-dimensional roughness profiles is presented. A primary field and a complete system of modal functions (radiation modes) are defined to be relatively simple in structure (plane-wave-type fields) and to satisfy the boundary conditions at the rough surface, individually and rigorously. These fields will not necessarily satisfy Maxwells equations. But compliance with these equations is enforced by the introduction of fictitious current distributions, associated with each of these fields, and chosen such that these ‘passive’ currents compensate for any field errors. In addition, each radiation mode is assumed to include an ‘active’ current distribution in the form of a current sheet which generates this mode. The composite field, formulated as a superposition of the primary field and the radiation modes, must be source free. It cannot involve any active or passive currents; and this zero-current requirement is then used to solve the scatter problem by an iterative procedure which, in a step-by-step fashion, eliminates the passive currents of the primary field and radiation modes by the active currents of the radiation modes. The result is a composite field that satisfies all requirements (Maxwells equations, boundary conditions and radiation condition) while all fictitious current distributions are eliminated by mutual compensation. This composite field is therefore the solution of the scatter problem. This new theory—involving fictitious current distributions—is unconventional. But after definition of the primary field and the radiation modes, it is straightforward and conceptually transparent. The first-order scatter pattern is reciprocal and bridges the gap between the small-perturbation method and the physical optics method. Since the passive currents quantify the field errors, the theory allows the establishment of an error criterion which indicates when field errors can be expected to be small. The results are compared with those of existing theories. The present paper presents the TE case; the TM case, which is more complex, will be described in a follow-on paper. (Some figures in this article are in colour only in the electronic version)