Theory of Radar Reflection from Wires or Thin Metallic Strips

Abstract

Knowledge of the radar response of wires or thin metallic strips, as a function of their length and thickness, and of the radar frequency is important in the design of reflectors for radar. In view of the difficulty of this theoretical problem and the necessity of making approximations, as well as the dearth of adequate experimental data, two independent procedures for solution are presented. Detailed quantitative results are obtained for the angular dependence of the cross section, and also for the mean cross section, of randomly‐oriented wires or, more generally, of metallic strips, which behave electromagnetically like cylindrical wires of a certain ``equivalent radius.'' When expressed in terms of a unit of area equal to the square of the wave‐length, these cross sections depend on the dimensions of the wire only through the two ratios $$\frac{\text{2l}}{a}=\frac{\mathrm{length\; of\; wire}}{\mathrm{equivalent\; radius\; of\; wire}}\mathrm{,\hspace{0.17em}}\frac{\text{2l}}{\lambda }=\frac{\mathrm{length\; of\; wire}}{\mathrm{wave-length}}$$ . >The mean cross section is shown to take on maximum values when 4l/λ is slightly less than an integer (n = 1, 2, etc.). The shift of these ``resonances'' from integral values depends on the ratio 2l/a, becoming greater as 2l/a decreases. The value of ${\mathrm{\sigma ̄/\lambda }}^2$ at resonance increases slowly with the order n of the resonance; it depends only very slightly on the ratio 2l/a, increasing as 2l/a decreases. For values of 4l/λ away from resonance, ${\mathrm{\sigma ̄/\lambda }}^2$ decreases rapidly, reaching minimum values near 4l/λ = 3/2, 5/2, etc. The value of ${\mathrm{\sigma ̄/\lambda }}^2$ at these minima is strongly dependent on 2l/a, increasing as 2l/a decreases. Also as 4l/λ increases, the heights of the minima increase and approach the height of the resonance peaks. A brief comparison with preliminary experimental results is given.