A uniform ray approximation of the scattering by polyhedral structures including higher order terms

Abstract

In this article, the authors attempt to treat both strong m i s t i n g and slight twisting of fiber via a consistent asymptotic approach to the coupled-mode theory. In strong twisting, an admirably simple and useful asymptotic equation is derived in the form R f = const., which relates the minimum required twist rate 7 with the minimum allowable radius of curvature R In slight twisting an oscillatory pattern of the polarization behauior clearly reveals the advantageous feature of a twist-spun fiber, which is made by a prior spinning of the fiber before a twi3ting. 0 1995 John Wiley & Sons, Inc. Received 11-30-94Microwave and Optical Technology Letters, 9/1,37-41 0 1995 John Wiley & Sons, Inc. KEY TERMS Complex pemrittiuq naeasmments, complex permeability measurements, pariialb filled waveguide ABSTRACTA partially filled waveguide is presented to measure complex permittivity and permeability simultaneously at microwave frequency in this article.The mode-matching method is used to analyze the higher-order modes in the waveguide. Experimental results a p e well with theoretical results. 0 I995 John uliley & Sons, Inc.

ITD formulation for the currents on a plane angular sector

“…9(a) and 9(b), respectively. The numerical results from the present formulation (continuous line) are compared with those from an MoM solution (dashed line, from [18]) The agreement is quite satisfactory. In the same figure, calculations are presented (dotted line) that have been calculated by applying the diffraction coefficients obtained in [20], which are the nonuniform (far-field) version of those derived in [21].…”

“…In the same figure, calculations are presented (dotted line) that have been calculated by applying the diffraction coefficients obtained in [20], which are the nonuniform (far-field) version of those derived in [21]. The two high-frequency methods very closely compare, as expected, except for aspects close to grazing, were integration of ITD currents; ----MoM (from [18]); 1 1 1 1 1 1 solution presented in [20]). …”

“…In particular, the fringe currents of each corner of the plate are integrated over the finite-plate surface, obviously retaining only one time the fringe contribution due to the singly diffracted rays arising from the same edge. The test cases that have been chosen are the same as that in [18], so that our results can be compared with other approaches based on first-and secondorder PTD [18]. It is worth noting that the integration of our fringe currents over the finite surface of the plate introduce an end-point-type description of the diffraction contributions associated to the following additional mechanisms: 1) interaction between nonadjacent edges; 2) interaction of each vertex with nonadjacent edges; 3) interaction between the DD field of two adjacent edge with a third edge (triple diffraction).…”

“…The formulation presented in [16], which is based on the extension of the spectral formulation given in [17] for parallel edges, also includes double interactions for soft polarization. In [18] and [19], the scattering from polygonal structures was treated within the framework of PTD including second order interactions; in [18] vertex contributions were also included.…”

“…The same formulation has been used in [21] to find, via spectral synthesis, a uniform solution for observation points at finite distances from the tip. The solution in [21] as well as other solutions presented in the literature [14], [18] are expressed in terms of a generalized Fresnel integral [22], which may appear to require significant computional efforts when the currents are used in a radiation integral. Nevertheless, the generalized Fresnel integral is essentially required to describe the field at those observation points where transition regions of different nature overlap; when the observation point is on the surface (i.e., when calculating the currents) such situations never occur, so that the currents may be conveniently described by ordinary Fresnel integrals.…”