Antenna Pattern Measurements of Weather Radars Using the Sun and a Point Source

Abstract

The sun is known to be a good target for weather radar calibration. In this paper high-resolution raster scans of the sun at high elevations will be used to derive the antenna pattern of weather radar, without being affected by beam propagation effects and reflections close to the earth’s surface. It is shown that this pattern matches well to pattern measurements using a point source. Hence, a good estimation of the real antenna pattern can be derived using the sun. Furthermore, formulas to extract undistorted antenna patterns from the sun, even at high-elevation angles, are derived. The signal processing required to achieve high sensitivity for the antenna pattern measurements will be described. Important parts of the antenna pattern—for example, sidelobes—become visible when using long integration times. The polarimetric receiver channel cross-correlation coefficient is proposed as a figure of merit of the cross-polar isolation of the antenna and hence the cross-polar pattern. The results are also compared to point source measurements. This illustrates how an unpolarized signal source like the sun can be used to derive polarimetric variables.