Hybrid Analog and Digital Beamforming Schemes for Airborne Radar: Resolving Angular Ambiguity in Weather Observations

An azimuthal (AZ) analog beamforming (ABF) followed by elevational (EL) digital beamforming (DBF) hybrid two-dimensional (2D) AESA architecture is proposed for airborne phased-array radar (APAR) to support complex weather observations. This hybrid ADBF structure mitigates the rigorous sensitivity demand and data bandwidth of fully 2D DBF receivers while still enabling elevational DBF capability. However, the ABF causes AZ angular ambiguity in the spatial matched-filter (SMF) process, due to the symmetric phase response along the azimuth in a symmetrical-weighted center (SWC) array. To address this issue, two asymmetrical-weighted center (AWC) schemes were proposed to resolve the AZ angular ambiguity. These schemes introduce nonlinear energy-weighted centers across 56 row-wise ABF subarrays, creating independent phase offsets that preserve azimuthal angular characteristics. A comprehensive 2D angular Design-of-Experiment (DOE) was conducted over angles up to 60° and signal-to-noise ratios (SNR) as low as -6 dB to evaluate the root-mean-square error (RMSE) of the estimated angles. Results show that the AWC schemes reliably achieve angular RMSE within 1° at SNR = -3 dB, whereas the SWC array consistently suffers from systematic angular ambiguity regardless of SNR or angular range.