Multiple-Scattering Resonances Between Parallel Conducting Cylinders

The results of numerical computations on the scattering of TM waves by two and three parallel conducting cylinders are described. Measurements of the diffracted field behind two 1.0λ, diameter conducting circular cylinders are compared with the predictions of approximate and exact formulations of the multiple scattering equations obtained through the multipole induction formalism. A feature of the experimental results is the occurrence of a null pair in the near field behind the array. These field singularities are also predicted by the exact formulation and are apparently a manifestation of multiple-scattering resonance. Polar diagrams of the currents induced on the surfaces of the cylindrical scatterers are presented for several sets of parameters. These diagrams show the occurrence of a resonant multiple-scattering phenomenon at critical values of cylinder separation under broadside illumination of the array. Calculations also indicate that with this illumination the forward scattering cross section of a two-cylinder array should display a characteristic maximum at a multiple-scattering resonance. Analogous resonant phenomena for the case of end-on illumination were not obtained and an explanation for this is proposed. A suggestion for the application of this resonance phenomenon is incidentally advanced, and it is also shown that the multipole induction formalism may be extended to scattering by noncircular boundaries.