Sidelobes reduction by using near field backward transform to correct aperture phase errors

The use of near-field probes has been recognized as an effective way to cut down costs in the development of array antennas. For most applications the near field data are processed through a 2-D FFT (fast Fourier transform) to obtain far-field patterns of the antenna under test, but the measured data can also be processed through a backward transform to reconstruct the aperture field for diagnostic purposes. A conventional diagnostic test was conducted with the probe almost touching the radome of the antenna in an attempt to resolve local defects. Due to the close proximity to the aperture, the probe interacts with the radiating elements, causing multiple reflections and diagnostic errors. To minimize the mutual coupling, the probe must be moved back from the aperture by a few wavelengths. At this distance, however, the effect of a discrete element fault tends to be averaged out by the radiation from other adjacent elements. To enhance the resolution, the backward transform technique is applied to project the near field back to the aperture plane, so that the amplitude and phase distributions can be recovered for diagnostics.<>