Near-field Focusing with Transmitarrays: Impact of Phase Quantization

The impact of phase quantization on the near-field focusing capabilities of a transmitarray antenna (TA) is numerically studied through a certain number of figures of merit (FoM), i.e. focus shift, depth of focus, spot size, and normalized power density. A numerical model to predict and analyze the electromagnetic-field distribution in the near-field region is first presented and validated through full-wave simulations at 300 GHz. This model takes into account the characteristics of the different building blocks of the antenna system (focal source, unit-cells, phase and amplitude of the transmission coefficient) as well as the TA geometry (focal distance, number of unit-cells) to synthesize the phase gradient required to generate a desired near-field distribution. Ideal focal source and transmissive unit-cells (UCs) are considered in the proposed FoM analysis. The numerical results show that the phase quantization does not affect focal spot and focus shift as opposed to depth of focus and normalized power density.