Analysis and Demonstration of Two Spherical Mode Expansion Resolution Algorithms

The measured radiation field of an antenna may be expanded in a series of vector spherical modes in a specified spherical coordinate system. Such an expansion may be resolved, by means of an iterative algorithm, into two constituent vector spherical mode expansions in two other specified spherical coordinate systems. The sum of these constituent expansions is equal to the original total radiation field. The purpose of such a resolution is to separate the radiation fields due to two identified parts of the original antenna which together constitute the entire radiating structure. Once the resolution has been accomplished, one may study the radiation from the currents on the two parts of the antenna individually including mutual interaction to all orders. This is to be distinguished from measurement of the radiation fields of the two parts individually because that measurement does not include the mutual interaction. A demonstration measurement of a two antenna system is described and iterative postmeasurement processing is employed to identify the radiation from currents on the two constituent antennas of the overall radiating structure. The results are compared with those of an earlier approximate noniterative algorithm developed for the same purpose and the differences are discussed.