On the Utility of Digital Beamforming in Weather Radars

Phased array radars (PARs) offer near-instantaneous sampling of the atmosphere when and where it is needed without mechanical inertia limitations. In addition, PARs offer the ability to synthesize different beam shapes from pulse to pulse. The advantage of agility that PARs offer is straightforward to understand and can be accomplished with lower tier PAR systems in terms of cost and complexity. On the other hand, the digital beamforming (DBF) that allows for the formation of receiving beams electronically using pre-collected IQ data samples, enabling significant flexibility in designing agile scan strategies, requires a higher number of digital channels which increases the PAR cost and complexity. Here, we discuss the practical use of DBF in weather radars. This study focuses specifically on the spoiled beam capability, where an intentionally broadened beam is transmitted while multiple simultaneous narrow pencil beams are digitally received. This capability allows for broader observational elevation/azimuth sectors within the same period, though it results in decreased sensitivity, increased two-way beamwidth, and higher sidelobe levels. Evaluating its scientific utility from both surveillance and tracking perspectives is essential, and this study aims to address this need. We examine two scenarios: an isolated convective cell and a mesoscale convective complex. Both cases were simulated using a numerical weather prediction model and radar forward simulator (CR-SIM). Using a dedicated instrument model, we simulated DBF capabilities with two pioneering C-band radars: PAIR (Polarimetric Atmospheric Imaging Radar) and APAR (Airborne Phased Array Radar), each representing ground-based and airborne PAR radar, respectively. We then quantitatively evaluate the surveillance performance of the spoiled beam in comparison to the pencil beam. Furthermore, we explore the effectiveness of the spoiled beam in enhancing situational awareness for tracking systems, comparing it with other surveillance approaches, such as low-elevation PPI scans and sparse elevation-azimuth scanning patterns.