UAV-Based Calibration for Polarimetric Phased Array Radar

Calibrating dual polarization in phased array radars is an important aspect of risk mitigation in moving towards a nationwide multifunctional phased array radar (MPAR) system for weather surveillance and to track aviation. Since dual polarization was implemented into the WSR-88D, the new products have been vital for hydrometeor classification. The calibration of scan-dependent polarization in phased arrays is a primary goal in achieving the same products provided by traditional dish-based systems. There are many challenges to the calibration process, including isolating the horizontal and vertical polarizations that are sent by the radar and making sure that their amplitudes are identical. In the project described herein, the focus is on the calibration of the radar’s receive patterns, the first step in the overall calibration process. An unmanned aerial vehicle (UAV) has been developed to facilitate scan-dependent calibration of a fixed phased array, and the focus of this part of the project is on the so-called “Twitching Eye of Horus” circuit.  It provides a means for transmission of calibrated horizontal (H) and vertical (V) electric fields towards the radar in a controlled manner from the UAV, but in and of itself it requires its own processing and calibration procedures. Removal of the frequency offset between the circuit and the radar is a primary challenge. This study takes a look at the process of calibrating the radar’s receiver using a UAV and the Twitching Eye of Horus, as well as presenting initial results.