Characterization of forward scattering parameters from an arbitrarily shaped cylinder by near-field probing

Abstract

The forward scattering from an arbitrarily shaped cylinder is characterized by its scattering pattern and the induced field ratio (IFR). Accurate calculation of these parameters for arbitrarily shaped and composite beams is in many cases time consuming, therefore analytical approximations are used. A combined experimental and numerical procedure for evaluation of these parameters based on near-field probing is presented as an alternative. This procedure is shown to be far more accurate than the analytical approximations presently used in calculations of the total scattering effect of tuned sandwich radomes. The results obtained by this method verify well with the scattering characteristics computed analytically or numerically by method of moments.

Forward-scattering analysis in a focused-beam system

“…In such a system, most of the energy is transferred from one feed horn to the other feed horn without significant losses and reflection interference from surrounding objects. The and coordinates of the lens contours can be computed by geometrical optics and are described by [3] (1) in which the subscripts 1, 2 designate the two opposite side contours of the lens, denote the lens thickness computed by (2) 0018-926X/98$10.00 © 1998 IEEE is the refraction index of the lens material. In analogy to the analysis of thin dielectric lenses [4], we define for each lens an equivalent focal length given by .…”

“…This procedure lacks the capability to measure its scattering pattern. Shavit [2] proposed an alternate technique to determine both the IFR and the scattering patterns of an arbitrarily shaped cylinder based on near-field probing.…”

“…The current paper describes a new combined experimental and numerical procedure to determine the scattering characteristics of arbitrarily shaped cylinders using a focused-beam system. In the proposed system, the IFR is computed based on measurement data and the scattering pattern is directly measured in contrast to the method suggested in [2], which requires postprocessing of the measured data. The unique features of the focused-beam system avoid measurement errors due to specular and diffuse reflections from adjacent objects, in contrast to the existing errors in an open measurement system.…”

Forward Scatter Radar for Air Surveillance: Characterizing the Target-Receiver Transition from Far-Field to Near-Field Regions

“…When an EM wave impinges on an obstacle, following the physical theory of diffraction (PTD), the scattered (diffracted) field can be viewed as generated by surface sources induced on the object by the incident wave [26,27,30]. In the forward direction, if the target dimensions are larger than the operating wavelength λ (a time-harmonic regime is assumed with λ = c/ f , where f is the carrier frequency and c the speed of light in vacuum), a shadow region is generated [7].…”

“…An exact evaluation of the field in the 'shadow' region of the target is thus achieved under the physical-optics approximation [7], valid when the target dimension is large in terms of the operative wavelengths. In order to emphasize the essential features of the problem, we will refer to a plane wave impinging on a metallic canonical shape [30], and the specific effects of possible near-field conditions are considered on the collected signal, since in many applications, the Rx antenna could be located at a few wavelengths from the moving target. In particular, an efficient analytical formulation for the scattered and total fields is carried out, which is valid for Rx both in FF and NF conditions, considering a rectangular silhouette (see Figure 1b) under first-order approximation in the phase expansion.…”