On the sidelobe performance of Fresnel zone plate antennas

The Kirchhoff scalar diffraction integral and the image method are used to investigate the close-in sidelobe performance of the simple and phase reversal circular zone plate antennas. It is found that, with fixed aperture dimension, the sidelobe level of a zone plate antenna depends mainly on N, the number of full wave zones composing the plate. When the aperture field taper is kept constant, the sidelobe level of the zone plate decreases significantly when N increases. This means that, with a given zone plate diameter, a small F/D is favorable for obtaining low close-in sidelobes. For a simple zone plate antenna, adequately lowering the edge illumination intensity does reduce the sidelobe level of a centrally opaque version, but it may raise the sidelobes of a centrally transparent one. For the phase reversal zone plate antenna, it is observed that versions with a central disk and a central aperture yield very similar radiation patterns with sidelobes lower than those of the corresponding simple zone plates. Adequately decreasing the edge illumination level produces lower close-in sidelobes.<>