Array Gain for Digital Beamforming Effects of Distributed Targets and Quantization

Abstract

Fully digital phased-array radars (PARs) have several advantages over conventional architectures, including flexible multibeam steering, adaptive beamforming, and signal-to-noise ratio (SNR) improvement in array gain due to the independence of receiver noise across array elements. However, the resulting data volume poses a significant bottleneck for real-time operation, requiring substantial data transfer bandwidth, processing resources, and storage capacity. In this study, uniform quantization is applied at the analog-to-digital converter (ADC) to reduce the data volume of element-level I/Q signals in the amplitude domain, and its impact on array gain is investigated through numerical simulation. Specifically, the analysis is conducted from two aspects: 1) array gain as a function of target distribution and 2) array gain as a function of quantization bit level. The results demonstrate that array gain is governed by the spatial correlation of the targets, indicating that it must be evaluated with respect to target distribution even with minimal quantization effects. Furthermore, the spatial characteristics of quantization noise are shown to depend on the steering direction. In simulations, the mismatch between the quantized projection weights and the beamforming weights reduces the correlation of quantization noise, resulting in its incoherent summation during beamforming and mitigating its impact on the beamformed output. Moreover, the spatial correlation of quantization noise across the array dominates the array gain characteristics as a function of steering angle.