Wideband Digital True-Time-Delay Compensation Techniques for Digital Arrays

Phased arrays use phase shifting to mimic time delay and are widely used due to their relatively simple implementation and low power consumption. However, phase shifting only approximates time delay, which is not identical to the actual time delay. Thus, phased arrays suffer from beam squinting and array inter-symbol interference. A baseband beamforming technique introduced in 1992 solves the squinting for acoustic beamforming. We apply this technique in RF beamforming by combining phase-shifting and time delay in the baseband. We describe a prototype true-time-delay digital beamformer built with an array of continuous-time bandpass sigma-delta modulators and bitstream processing.