Airborne polarimetric Doppler weather radar: Trade-offs between various engineering specifications

Abstract. NCAR/EOL is investigating potential configurations for the next generation airborne phased array radar (APAR) that is capable of retrieving dynamic and microphysical characteristics of clouds and precipitation. The APAR will operate at C-band. The APAR will use the electronic scanning (e-scan) feature to acquire the optimal number of independent samples for recording research quality measurements. Since the airborne radar has only a limited time for collecting measurements over a specified region (moving aircraft platform ~ 100 m/s), beam multiplexing will significantly enhance its ability to collect high-resolution, research quality measurements. Beam multiplexing reduces errors in radar measurements while providing rapid updates of scan volumes. Beamwidth depends on the size of the antenna aperture. Beamwidth and Directivity of elliptical, circular and rectangular antenna apertures are compared and radar sensitivity is evaluated for various polarimetric configurations and transmit/receive elements. In the case of polarimetric measurements, alternate transmit with alternate receive (single channel receiver) and simultaneous reception (dual channel receiver) is compared. From an overall architecture perspective, element level digitization of transmit/receive (T/R) module versus digital sub-array is considered with regard to flexibility in adaptive beamforming, polarimetric performance, calibration, and data quality. Methodologies for calibration of the radar and removing bias in polarimetric measurements are outlined. The above-mentioned engineering options are evaluated for realizing an optimal APAR system suitable for measuring the high temporal and spatial resolutions of Doppler and polarimetric measurements of precipitation and clouds.