UAV-Based Antenna Measurements for Polarimetric Weather Radars: Probe Analysis

One of the principal challenges in the calibration of polarimetric weather radars is achieving the strict requirements in the measurement of the antenna radiation pattern of the system; e.g., a co-polarization mismatch of at most 0.1 dB, and cross-polarization levels less than approximately -40 dB are highly desirable. In a UAV-based antenna pattern measurement system, the radiation characteristics of the probe antenna can be adversely affected by scattering off of the UAV platform itself, and by the relative orientation of the probe antenna with respect to the UAV frame. It is hypothesized that such extraneous reflections depend on the type of antenna used as a probe, and in this context, a more directive probe antenna (i.e., with low back lobe radiation) would be necessary to achieve the required measurement accuracy for weather radar applications. This work studies the effect of UAV and probe antenna interaction for different types of antennas through EM simulations, and this is validated with chamber measurements. For the patch array antenna under study, co-polarization mismatch levels of approximately 0.13 and 0.05 dB, and maximum cross-polarization levels of -37 and -34 dB, are achieved at boresight in measurements and simulations, respectively, which can be improved to meet the requirements with a careful selection of the gimbal operating angle range.