Dielectric nose radome scattering by using the fast multipole method to calculate the RCS of large objects

Nose radomes serve as enclosures for antennas and are generally pointed to reduce aerodynamic drag. The performance of a radome is generally described by parameters which include the far-field radiation pattern, power transmittance, boresight error and boresight error slope. Approximate methods for treating the propagation of the plane wave through a radome include high frequency techniques which typically consider the radome to be locally plane and omit guided waves as well as interactions between the radome sections. Also, treatments of the higher order interactions between the radome and the antenna have so far received little attention. Clearly, a more accurate approach is to employ an exact analysis method such as the moment method technique which is capable of including all first and higher order phenomena. However, due to the traditional O(N/sup 2/) storage and O(N/sup 3/) CPU requirements the method of moments approach can only be used for small radome structures. A number of techniques have been introduced which can reduce the CPU requirements down to O(N/sup 1/.5) or less for large scale simulations. The fast multipole method (FMM) is one of these techniques and accomplishes the CPU reduction by lumping the far zone moment method elements into groups. The groups are subsequently interacted (rather than the elements) to achieve the purported CPU reduction. In the FMM implementation, the near-zone and self-cell elements are evaluated unaltered and thus the accuracy of the original method of moments formulation is retained.