Spherical near- to far-field estimation from amplitude measurements.

Abstract

Characterizing electromagnetic field produced by radiators in their operational modes is of primordial importance in various engineering application such as antenna design, compatibility and interference testing. The far-field pattern is the most common measure, but it is often impractical and at worst impossible to measure the far-field directly. Numerical methods implementing near- to far-field transformations rely on the knowledge of both the amplitude and phase distribution on a surface in proximity of the device under test. In certain instances however, it is expensive or very difficult to accurately measure the phase distribution component. The intent of this thesis is to investigate the feasibility of near- to far-field transformation with the premise that only amplitude distribution component is available. The requirement is thus to provide, or estimate, the missing information necessary for near- to far-field transformation. The retained approach implements the well known spherical wave expansion technique. The coefficients of the spherical wave functions depend on the boundary conditions, and due to their incomplete knowledge only bounds for those coefficients can be calculated. Application of heuristic methods to the estimation of the coefficients, and upon the assumption of the uniqueness of the solution, are sufficient to predict the radiated fields. This method presents an important advantage over direct phase distribution estimation in that the number of coefficients is well defined and can generally be expected to be less than the required number of phase measurements.