A Polarimetric Antenna-Calibration Method for the Horus Radar Based on E-Field Back Projection

Phased Array Radar (PAR) technology can provide tailored, high-quality meteorological observations and is rapidly rising as a candidate for future weather radars. To conduct precise measurements of polarimetric weather variables, it is desired that the radar transmits and receives linearly polarized horizontal (H) and vertical (V) fields through beams well matched in gain and shape at every scanning direction. These characteristics are difficult to achieve because the radiation patterns of phased array antennas inherently depend on polarization, beam shape, and gain in the intended pointing direction. Polarimetric array calibration is critical to produce symmetric and matched co-polar antenna patterns at the two polarizations. In this paper, we present a new polarimetric antenna calibration procedure for the all-digital Horus radar based on holographic back projection of electric fields. Near-field Horus measurements are back-projected onto the plane of the array to derive the co-polar magnitude and phase of the H/V fields radiated by each antenna element. Digital calibration parameters are derived from back-projected fields to compensate for excitation differences and produce uniform radiation at the plane of the array. Preliminary results show that through digital calibration based on back-projected fields, co-polar H and V beam matching can be considerably improved. This naturally improves polarimetric measurement accuracy of the Horus radar by mitigating antenna-induced biases in meteorological estimates.