Nonuniform Amplitude Transmitarray for Multibeam Including Near-Field Focusing

This article presents a nonuniform amplitude transmitarray for a multibeam that includes near-field focusing, based on a frequency selective surface (FSS). Each cell on the FSS is fed by a slot array and its feeding magnitude is adjusted by the slot position. The phase sets required for near-field focusing and far-field steering are controlled by the cell size of the FSS located above each slot. To confirm the performances of the antenna, a multibeam antenna for beam focusing and steering is designed. The required phase and amplitude of each cell are simply calculated and optimized by the principle of superposition. Finally, a 6 \times 4 array prototype antenna operating at 5.8 GHz is realized, and its characteristics are measured. The antenna can simultaneously focus on a near-field spot and radiate in the desired far-field direction. The measured and simulated results are found to be in good agreement.