1,721,234 research outputs found
A uniform double diffraction coefficient for a pair of wedges in arbitrary configuration
No full textIn this paper an analytic closed-form solution is presented for the double diffraction at a pair of arbitrarily placed wedges that is suitable to be used in a uniform theory of diffraction (UTD) ray description framework. Here, the particular assumption, present in all the past literature, that the two diffracting edges are coplanar is removed. The doubly diffracted (DD) field at a pair of wedges is constructed via spectral synthesis. Such a procedure provides a double spectral integral representation of the DD field that is asymptotically evaluated by resorting to transition functions, typical in double diffraction problems, that can be expressed in terms of generalized Fresnel integrals. The final expression is arranged in the typical UTD fashion and contains a uniform double diffraction dyadic coefficient. The DD field behavior is analyzed in its transition regions to show how the DD field smoothly compensates for the total field discontinuities occurring at shadow boundaries where a singly diffracted field from a wedge is shadowed by the other wedge. Numerical examples are provided to verify such analysis and to test the accuracy of our UTD ray description against method of moments full wave results. © 2005 IEEE
Stochastic Theory of Edge Diffraction: An Alternative Formulation
No full textAn alternative formulation is presented for the derivation of the results in [1] which allows to rigorously extend the validity range to any incidence/observation aspect provided that the standard deviation \sigma of the edge roughness is not large compared to the wavelength \lambda while the observation distance r is r>>\lambda. This was heuristically conjectured by Franceschetti, et al. (IEEE Trans. Antennas Propag., vol. 56, no. 2, pp. 437- 449, 2008) and supported by numerical examples, but without a rigorous
proof
Boundary Diffracted Wave and Incremental Geometrical Optics: a Numerically Efficient and Physically Appealing Line-Integral Representation of Radiation Integrals. Aperture Scalar Case
No full textThis paper presents a novel formulation to reduce radiation integrals to line integrals. Such a reduction is exact for Kirchhoff aperture radiation integrals and physical optics (PO) scattering from flat soft/hard (perfectly conducting) plates, illuminated by a spherical source, but can be effectively extended in an approximate version to more general configurations. The advantage of our approach is that the integrand of the line integral along the rim of the radiating surface is free from singularities and can be easily integrated at all the observation aspects, including geometrical optics shadow boundaries. Conversely, at those aspects, existing formulations exhibit, in the integrand, a pole singularity that renders the numerical integration inaccurate or time consuming, since it requires adaptive integration routines. This was a main concern in the use of this kind of approach for the time reduction in the numerical calculation of aperture/scattering radiation integrals, which is overcome by our approach. Also, the novel result presents a neat ray interpretation which is physically appealing and allows for the heuristic extension of the approach to non-exact cases (e.g., arbitrary impedance boundary conditions or curved surfaces) using standard ray approximations. Beside the already known boundary diffraction wave (BDW), which is an incremental wave excited by the incident field and arising from the rim of the surface, a further term called incremental geometrical optics (IGO) is introduced. This novel term is an elementary portion of the direct field arising from the source and impinging at the observation point; it is able to cancel the BDW singularity thus rendering the whole integrand smooth. For the sake of simplicity, the BDW + IGO theory is here presented with reference to the simplest scalar case of aperture radiation. © 2010 IEEE
An Exact Line Integral Representation of the PO Radiation Integral from a Flat Perfectly Conducting Surface Illuminated by Elementary Electric or Magnetic Dipoles
No full textIn this paper, a line integral representation for the PO radiation integral from a flat perfectly conducting surface, illuminated by an arbitrary oriented elementary either electric or magnetic dipole, is presented. No restriction is imposed on the position of the source and of the observation point. The main application of this result is the acceleration of the numerical PO integration for electrically large surfaces. The formulation is based on the application of the equivalence principle to a projecting surface which allows the analytical evaluation in closed form of one of the two-fold surface integral which define the radiated field at any space point. Although similar solutions has been suggested by other authors, our final outcome is simple, clearly interpretable, and easily applicable with respect to previous results
Truncation Effects in a Semi-infinite Periodic Array of Thin Strips: A discrete Wiener-Hopf Formulation
Full text linkrigorous solution for the current induced on a semi-infinite array of narrow metallic
strips is obtained using the Wiener-Hopf factorization method in the Z-transformed
domain. The method can be applied to arrays with fixed current shape on each element
(e.g, single mode elements), and shows rigorously the physics of waves associated to
truncated periodic structures. The solution is obtained via a rigorous factorization, that is
improved by using a closed form result based on an approximated factorization. The
current on the truncated array is rigorously represented as the sum of the current pertaining
to the infinite array plus a contribution induced by the truncation of the array. Asymptotics
shows that the truncation-induced current contribution has a diffractive behavior decaying
algebraically with the element number, away from the truncation. Uniform asymptotics
shows that this diffractive current is effectively represented in terms of Fresnel functions,
permitting also a closed form representation in proximity of and at transverse inward
resonance, i.e., when a grazing grating lobe points toward the array. Illustrative examples
and comparisons with a method of moment solution show the accuracy of our results
Uniform Double Diffraction Coefficient for a Pair of Wedges in Arbitrary Configuration
No full textThis monograph contains the ceremonials and proceedings of the Workshop / Minisymposium on "Electromagnetics in a Complex World: Challenges and Perspectives", convened at the University of Sannio, Benevento, Italy from February 20-21, 2003, in connection with the bestowal of an honorary Laurea degree on Professor Leopold B. Felsen. The various contributions from scientists and engineers in academy and industry address diverse problems in electromagnetics, either on a broad scale or in particular specialties. The wide-ranging topics and techniques, analytic models (with phenomenologies) and numerical simulations - motivated by actual or potential applications to real-world problems - are intended to stimulate interdisciplinary exchange
Planar metamaterial transverse equivalent network and its application to low-profile antenna designs
Full text linkWe present a lumped circuit description of a novel metamaterial layer made of arrayed pairs of tightly coupled conductors (dogbones or Jerusalem crosses). This lumped element network is synthesized to exhibit the same frequency response of the metamaterial layer when inserted in the plane-wave equivalent transmission line. The metamaterial and its transverse equivalent network (TEN) model is then applied to the design of a high impedance surface for low profile dipoles and a partially reflective superstrate for highly directive Fabry-Perot cavity antennas. Numerical results illustrating the radiation properties of such antennas are provided
EBG superstrates for dual polarized sparse arrays
Full text linkA superstrate of an EBG material (or equivalently a Fabry-Perot cavity) is used to design array antennas with large distance between the radiating elements. This configuration provides some advantages: (i) a reduction of the number of array elements to achieve high directivity; (ii) large space between contiguous elements decreases their coupling and permits an easy arrangement for a complicated feeding network (as needed for dual polarization), also on the same plane of the radiating elements. These possibilities are clearly shown in a few examples treated here and in the design of dual polarized antennas with two interleaved arrays. Furthermore, we indicate that in these designs there are optimum distances between elements that either maximize the directivity or minimize the sidelobe level. It is also shown that due to the fact that the radiating elements have larger-than-usual mutual distances it is easy to achieve -40dB of isolation between the two excitation ports, for the two polarizations
Influence of the finite conductivity on RLSA antenna design
No full textIn this paper, we consider the effect of the finite conductivity on the design of a radial line slot array (RLSA). Such an effect can be not negligible at high frequencies, especially when low cost metallization techniques are adopted. We show how this effect can be easily introduced in the numerical modeling of the antenna. As a matter of the fact, we extend the analytical evaluation of the dyadic admittance Green's function to the case of a low, arbitrary impedance surface, and we use it within a Method of Moment (MoM) for RLSA. The results of the MoM numerical simulations have been tested against those by commercial codes for different conductivity values
An asymptotic evaluation of radiation surface integrals for high frequency wave problems which reduces to the UTD ray format
No full textThe field scattered by a scattering body or by an aperture in the free space (or in an unbounded homogenous medium) can be described in terms of a double integral. In this paper we present a new asymptotic uniform evaluation for this kind of integrals that is expressed in the format of the uniform geometrical theory of diffraction (UTD), which is convenient for numerical computations
- …
