A True Time Delay 16-Element 4-Beam Digital Beamformer

Large phased arrays are limited by inaccurate beam steering (squinting) and by distortion in analog-to-digital conversion. This paper introduces the first integrated digital true time delay beamforming receiver. The true time delay eliminates squinting, making it ideal for large-array wide-bandwidth applications. The beamformer incorporates a new current-steering DAC architecture providing a constant output impedance to improve ADC linearity. This significantly reduces distortion, leading to an SFDR improvement of 13.7 dB from the array. The prototype achieves an EVM better than -37 dB for 5 MBd 256-QAM and 512-QAM. The measured beam patterns are near-ideal for both conventional and adaptive beamforming. The prototype digital beamformer supports 16 antennas and 4 independent beams. It occupies only 0.29 mm(2) and consumes 453 mW.