Time-Delay Digital Beamforming with 1.3GHz Bandwidth Using Direct RF ADC

Radar system has been using a hybrid of analog and digital beamforming. Sub-arrays of phase shifters in the analog domain are digitized at the sub-array outputs for further digital beamforming processing. Such system suffers from several drawbacks including not being able to create more than one simultaneous beam. Digital time delay beamforming brings many benefits such as wide bandwidth pulse waveform and simultaneous beams at different angles, wave forms and frequencies, with improved agility of scans between angles. Such capabilities may have been deemed too expensive in the past, but is now within reach due to the high density of multipliers in the FPGA and introduction of direct RF ADC (Analog to Digital Converter) that support high sample rates. This paper will present the design and implementation of a fractional delay (FD) filter used in time delay digital beamforming with 1.3GHz bandwidth running on Intel direct-RF FPGA with integrated data converters. Other beamforming issues like channel synchronization, including latency and phase alignment, and compensation for baseband delay are also investigated.