Multilevel fast near-field far-field transformation for electrically large antennas

Near-field antenna measurements combined with a near-field far-field transformation are an attractive alternative to direct far-field measurements. In order to compensate the field probe influence, a probe correction is required to obtain accurate transformation results. The widely applied spherical multipole techniques become impractical for higher order probes and irregular measurement grids, since fast Fourier transform based correction algorithms can no longer be applied. This paper presents a fast multilevel approach of the near-field far-field transformation based on plane wave expansion and diagonal translation operators, which is related to the multilevel fast multipole method known from method of moments solution of integral equations.