Measurement distance requirements for both symmetrical and antisymmetrical aperture antennas

Universal curves giving the main-lobe reduction and the first sidelobe level change versus the measurement distance are furnished for various aperture distributions. The widely used Rayleigh 2D²/λ distance criterion (where λ is the radiated wavelength and D is the distance to the antenna) is shown to be unsatisfactory, since the minimum measurement distance depends both on the aperture distribution and on the specific far-field parameter under measurement. It is found that, in order to measure accurately the pattern of antennas with ultralow sidelobes, a measurement distance much greater than the Rayleigh one is needed. Such a distance is more than safe for measurement of the antenna gain and antenna patterns with moderate sidelobe level, but it is greater than necessary to measure the principal parameters of interest in a monopulse system. This latter conclusion is in full agreement with reported experimental results. Some experimental results concerning a monopulse antenna reported