Design parameters for zone plate antennas

The design parameters of the circular Fresnel zone plate are the diameter, focal length, frequency, degree of phase correction, and dielectric material. An experimental design was carried out at 35 GHz for both a transmitting and a reflecting zone plate. It is shown that the rings on the lower half of the zone plate are almost circular, while the rings on the upper half of the zone plate are slightly elliptical with an eccentricity of about 1.20. As beta increases, the eccentricity decreases. The resulting zone plate, therefore, is not much different from a zone plate with an on-axis feed and circular rings. This explains the relatively good performance of such a zone plate when its feed is moved off-axis by as much as 20 degrees . If beta is larger than 20 degrees , then the elliptical design procedure should be implemented to obtain maximum intensity at the focal point.<>