## 1. Introduction

[2] It is well known that Gaussian beam can give a better simulation of radar beam than plane wave. Therefore, in recent years, the problem of scattering of a Gaussian beam by composite scattering models has been the subject of extensive investigations. Because of the simplicity of the geometry and the interest in practical applications, scattering of plane wave or Gaussian beam by isolated cylinders or spheres has been well studied both theoretically and experimentally [*Wu and Guo*, 1997, 1998; *Zimmermann et al.*, 1995; *Chen and Cheng*, 1964; *Wu and Wei*, 1995; *Gouesbet et al.*, 1990; *Doicu and Wriedt*, 1997; *Wang*, 1985]. However, when the composite scattering field from discrete random media is studied, the interactions of electromagnetic wave between different scatterers should be taken into account. Because of the important influence on total field, higher-order scattered field has attracted the attention of many researchers. Unfortunately, to obtain the solution up to higher order, it is necessary to treat the electromagnetic interaction between objects that is not only nonplane wave in character but have nonuniformities in amplitude and phase. For this type of the problem, the exact analytical solutions cannot be found except for a very small number of cases [*Yokota et al.*, 1986; *Elsherbeni and Hamid*, 1987; *Hongo*, 1978; *Elsherbeni et al.*, 1993]. To overcome these difficulties, a new technique based on the reciprocity theorem [*Sarabandi and Polatin*, 1994; *Li et al.*, 1998; *Chiu*, 1998; *Kong*, 2000] is proposed by *Sarabandi and Polatin* [1994] to evaluate the composite scattered field from two adjacent targets and an approximate solution for the scattered field up to the second order is obtained. However, the initial formulae, which are used to evaluate the second-order scattered fields, take the form of volume integral. In our work, the technique proposed by Sarabandi is improved by introducing the surface equivalent electric current and surface equivalent magnetic current [*Kong*, 2000]. Then, the higher-order solutions are simplified from the volume integral form to the surface integral form (for three dimension scattering problems) or the line integral form (for two-dimensional scattering problems). Thus the difficulty in evaluating the higher-order scattered field is reduced. On the basis of the improved technique, an approximate solution up to *N*th order for the scattered field of a Gaussian beam from an array of *N* parallel adjacent two-dimensional (2-D) targets is derived. In this calculation, only the previous-order scattered field of objects and the equivalent surface electric and/or magnetic current density induced by the incident beam are required.

[3] Because plasma can efficiently absorb electromagnetic waves, it can be used as microwave absorbers [*Laroussi*, 1993; *Liu et al.*, 2002; *Tang et al.*, 2003; *Robert*, 1990]. The absorption is mainly dependent on several parameters such as the electron number density, the radar frequency, the thickness of plasma layer, as well as the momentum transfer collision frequency, etc. Therefore, in section 3, the technique proposed in section 2 is applied to obtain an approximate analytical solution for composite scattering field from *N* inhomogeneous plasma-coated conducting cylinders when they are illuminated by a Gaussian beam. In section 4, the bistatic and the monostatic scattering are discussed and the results are compared with numerical computations based on the time domain integral equation method. The dependence of attenuation of the scattering width on the thickness of the coated layer, the electron number density, the collision frequency and the radar frequency is discussed in detail.