Modeling and Design of Offset Parabolic Reflector Antennas using Physical Optics and Multilevel Fast Multipole Method Accelerated Method of Moments

Modern radio, wireless and satellite communication and radar systems often involve electrically large and arbitrarily shaped metallic surfaces those span many wavelengths in three dimensions. High frequency asymptotic techniques e.g. current based physical optics (PO), ray based uniform theory of diffraction (UTD) represent approximate forms for solving radiation and scattering problems, and more accurate solutions are sometimes desired. Exact numerical results can be found by solving integral equations (IE´s) using the method of moments (MoM). Application of the moment method to an integral equation yields full coupling matrices resulting in bad computational complexity and more importantly memory resources are fastly becoming insufficient for large objects. Recently a multilevel fast multipole method (MLFMM) accelerated MoM technique has been implemented for the efficient and yet accurate solution of radiation and scattering problems for arbitrarily shaped electrically large structures. The MLFMM-MOM scheme provides accurate solutions in the regions where asymptotic techniques do not produce good results. This approach is used for the numerical computation of radiated fields of offset parabolic reflector antennas. Excellent agreement of physical optics results in the main lobe and out to several lobes has been found with those of MLFMM accelerated MoM technique. Because of current singularities at edges of reflector and absence of feed coupling effects in physical optics formulations, significant deviations of PO results are observed in far side lobes. Review of the computational techniques is presented and numerical results for two reflector antennas are shown.