Evaluating the Calibration Stability of an Active Phased-Array Weather Radar

Active phased-array radars produce agile beams with shapes and sidelobe levels dictated by the phase and amplitudes of the radiating elements. The nominal settings of the array are determined through a calibration procedure which accounts for various phases and amplitudes of the microwave components comprising the active array elements. Deviations from these nominal settings occur due to temperature and other environmental changes which can affect the beam properties. The stability of relative amplitudes and phases among array elements is critical to the beam quality, and hence the quality of derived weather products.

The UMass Phase-Tilt Weather Radar, an X-band dual-polarization active phased-array, is used to evaluate the stability through repeated measurements over a variety of environmental conditions. Self-diagnostics based on mutual coupling performed in the field, and field observations of linear depolarization (LDR) in light to moderate precipitation are compared to laboratory-based calibration and near-field antenna chamber measurements. The implications for other active phased-array weather radar systems in development, such as the NCAR Airborne Phased Array Radar, are discussed.