Micro-beamforming with Error Compensation.

Abstract

One of the main issues in the development of 2D arrays is the high system complexity due to the requirement for a large number of elements. 2D array systems suffer from high system complexity. Micro-beamforming (MBF) method has been proposed to reduce the system complexity; however, distortions of MBF approach such as focusing errors of post-beamforming process results in broadening the main lobe and increasing the side-lobe and grating-lobe levels, which together degrade the image quality. As the pre-steered radio-frequency (RF) data can be estimated from MBF data at the digital back end, better post-beamforming can be performed and higher image quality can be achieved. In this study, a compensation approach is proposed to estimate the pre-steered RF data from MBF data by utilizing additional headers and compensation factors. The compensation factors and headers are estimated at the probe front end and then applied to the back-end digital system to reconstruct the required pre-steered RF data. As the absolute values of the MBF errors are modeled as a single-sided Gaussian distribution, the theoretical mean square error (MSE) with the proposed method is approximately 2.75 times lower than that of its counterpart without compensation; this implies better reconstruction of pre-steered RF data can be achieved with the proposed method. The simulation results showed that the main lobe is improved, and the side-lobe and grating-lobe levels in both the lateral and elevation directions were improved by 11.73 dB and 19.12 dB, respectively, while the peak signal-to-noise ratios improved by 6-9 dB with the proposed method. The contrast-to-noise ratios also are enhanced by 0.5 dB when using the proposed method. Analog circuits are presented to demonstrate that this novel compensation method can be realized in practice. The reduction of cables and analog-to-digital converters (ADCs) are about 7-fold compared to fully-sampled 2D array systems as 4 by 4 channels are grouped for the proposed method as well.