Unmanned Aerial Systems (UAS) are a novel solution for antenna measurements. Due to their flexibility and portability, they are an ideal solution for in situ measurements of large antennas. However, measuring large antennas in situ, i.e., outdoors, introduces environmental errors due to wind, among others. The substitution method is an established approach to measure an Antenna Under Test’s (AUT) gain.

The method is based on the knowledge of the gain of a reference antenna: the gain standard. However, this method relies on the mechanical precision of the acquisition system, since measurements not acquired exactly at the maximum of the main lobe of both antennas introduce error. This becomes especially critical for flexible positioner systems such as UAS. In this work, the gain of an offset parabolic reflector antenna, the AUT, is estimated using a Standard Gain Horn (SGH) through outdoor measurements. The gain estimated is compared to measurements performed in ESA-ESTEC’s facilities.

The maximum of the main lobe is determined by performing a fine raster scan with the UAS in the AUT’s far field, which is then interpolated for the determination of the maximum. Then, that point is continuously scanned by the UAS for a certain time to compensate for errors introduced by in-flight vibrations due to the system itself and to external elements, such as wind gusts. In this work, the analysis to estimate the required measurement time, as well as its validation through measurements, are presented.