Spherical Near‐Field to Far‐Field Transformation

This chapter presents two methods for spherical near‐field to far‐field transformation. The first methodology presents an exact explicit analytical formulation for transforming near‐field data generated over a spherical surface to the far field radiation pattern. The second method presents the equivalent source formulation that was described earlier and illustrates how it can be deployed to the spherical scanning case where one component of the field is missing from the measurements, when the tangential components of the fields on a spherical surface is given. Near‐field scanning over canonical surfaces—planar, cylindrical, and spherical—is often used to obtain the far‐field pattern characteristics of an antenna under test via near‐field to far‐field transformation algorithms. A comparison with the technique based on the spherical wave‐mode expansion has been performed in terms of far‐field results.