Investigation of the Extent of the Fresnel Region of Aperture Antennas with Attention to Superdirectivity

摘要

This technical note describes the principles governing superdirective antennas and the factors limiting their realization. A criterion for determining the minimum distance to the far field of aperture antennas, including superdirective antennas, is presented. Under this condition it is shown that, at least for the marginally superdirective case, such antennas do not exhibit large fresnel regions as compared with minimum distance to the far field in a given direction. Under this criterion it is shown that for the uniform distribution, the antenna pattern near nulls requires a large distance to converge to the far field form. This work has applications in determining antenna test range requirements. Canada. (rrh)