Abstract
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.
Highlights
With the introduction of dual-polarized multifunction phased array weather radar systems (MPAR) [1] as a replacement for the current dish-based weather radar system (WSR-88D), additional challenges arise in the characterization and calibration of their components to ensure that no biases are being introduced in the polarimetric weather radar products [1], [2]
0◦ gimbal yaw, while between −5◦ and 5◦ the variance is tolerable. This supports the idea that by limiting the operating range of gimbal yaw angles, the effects of the UAV on the radiation characteristics of the probe antenna can be mitigated to some extent, and provides an insight on how the probe antenna behaves as a function of its orientation relative to the UAV frame
One of the most important is the degradation of the radiation characteristics of the probe antenna due to being in the proximity of the UAV frame
Summary
With the introduction of dual-polarized multifunction phased array weather radar systems (MPAR) [1] as a replacement for the current dish-based weather radar system (WSR-88D), additional challenges arise in the characterization and calibration of their components to ensure that no biases are being introduced in the polarimetric weather radar products [1], [2]. Such performance can be improved if the variation of the relative alignment between the UAV and the probe is sufficiently small (i.e., within a few degrees off boresight). As previously mentioned, this performance can be improved by constraining the relative alignment between the probe and UAV to within a few degrees from boresight. The array is selected as the probe antenna to be mounted on the UAV, since it has the best performance overall, when RF and flight performances are taken into account
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