OFFSET FRESNEL ZONE-PLATE ANTENNAS

The theory of offset Fresnel zone plate antennas is presented. Explici t formulae for the design of the zone boundaries for the offset Fresne l zone plate are given. Theoretical equations and numerical results fo r the far-field analysis are presented. It is found that when the offs et angle increases, the zone boundaries become more elliptic and the p late becomes more asymmetric in the E-plane. With the number of full w ave zones and the plate width in the H-plane fixed, the plate width in the E-plane increases with the offset angle, which keeps the projecte d aperture area constant. Within a limited range of offset angles, the offset configuration can be employed without degrading the radiation performance much. For large offset angles, however, the asymmetry of t he configuration may lead to increased sidelobes and decreased antenna directivity. An experiment with one particular phase reversal zone pl ate antenna with 30-degrees offset angle shows good agreement between the measured antenna pattern and the theoretical prediction.