X-Band Phased-Array Weather-Radar Polarimetry Testbed: Tilted Aperture Bias Correction Results

The University of Massachusetts continues our experiment on phased-array weather radar polarimetry. We aim to quantify electronic scan polarization errors and demonstrate methods for polarimetric bias correction of weather radar measurables. The study uses a weather radar testbed consisting of two dual-polarized X-band radars. The first is the Low Power Radar (LPR), developed by Raytheon, which uses a 2560 element planar phased array antenna that can electronically scan in both azimuth and elevation. The second is the UMass EXperimental X-Band Radar (UMAXX) which uses a mechanically scanned parabolic dish antenna. Both radars are mounted on a 70-foot tower and operate simultaneously, so that the phased array can be calibrated using the dish radar as a reference in real time.

The LPR uses dual-polarized microstrip patch elements operating at 9.6 GHz and supports both pulse and chirp transmit waveforms. It operates in alternate transmit, alternate receive mode (ATAR). The scan range is 90 degrees in azimuth and 30 degrees in elevation (array panel is tilted so broadside is at 15 degrees elevation). UMaXX uses a magnetron transmitter at 9.4 GHz to transmit and receive in both vertical and horizontal polarizations simultaneously (STSR), but can also measure LDR by redirecting the vertically polarized to a load on transmission. Both radars operate with a similar frequency, sensitivity and beamwidth to allow for easier comparison of collected data.

Weather data has been collected using both radar systems during the fall of 2018 as well as the summer of 2019. Polarization biases are a result of the projection of tilted aperture polarizations to world-relative coordinates, but also depend on the antenna element amplitude and phase patterns. The effectiveness of calibration using quasi-vertical scans is compared with calibration using embedded element patterns, using UMaXX measurements as a reference in both cases.