Increasing direction-of-transmission resolution in digital time-delay beamformers

The direction-of-transmission (DOT) resolution of a digital time-delay beamformer (DTDBF) is directly related to sampling intervals. In fact, the smaller the sampling intervals the better the DOT resolution and the larger the number of natural beams. In a DTDBF based on digital signal processor (DSP) the sampling intervals are primarily restricted by the I/O bandwidth of the DSP. In this paper a new and simple digital time-delay beamformer configuration for transmission is proposed, incorporating a programmable delay line (PDL) between DSP and digital-to-analog converter (DAC). The behavior of the resultant system is first analyzed and then compared to the traditional one through simulations. It is proven that the proposed system significantly increases the DOT resolution and overcomes DOT accuracy errors opposed to that of the conventional one. Furthermore, the influences of the additional time jitter effects due to PDL and DAC objects on the performance of the proposed system are investigated.