amplitude due to the frequency windowing: α = 0.5442 in the case of a Kaiser window with β = 5. The SYMA quadcopter was placed over the platform and a complete measurement with antennas in vertical polarization was car- ried out. The distance between the antennas and the rotation center was 156 cm. The angular step was 1 deg. By using a Kaiser window with β = 5, a 500 MHz bandwidth gives a Full Width at Half Maximum (FWHM) equal to 0.54 m (larger than the size of the quadcopter). The measured angular pattern of RCS is shown in Figure 4. The largest values are in correspondence of the four motors. The measured main value of the RCS was 0.0312 m2. By rotating the antennas, the RCS of the SYMA quadcopter was also measured in horizontal polarization. The obtained main value has been 0.0229 m2. There are not substantial differences with respect to the RCS pattern in vertical polarization. The same measurements have been performed with the AirVision quadcopter. The measured angular pattern of RCS in vertical polarization is shown in Figure 5. For this quadcopter, the largest RCS values are in front and back. The main value is 0.271 m2. By rotating the antennas, the RCS of AirVision quadcopter was also measured in horizontal polarization. The obtained main value has been 0.2759 m2. There are no substantial differences between the RCS patterns in horizontal and vertical polarizations. Table 1 summarizes the obtained results. Just a note about the distance between antenna and target: for both the UAVs it was 156 cm. The RCS of a target should be measured in the far field both of antenna and of target. The first Figure 2. Figure 3. THE UAVS UNDER TEST As a representative toy drone we selected a SYMA X5SC-1 quadcopter (Figure 2). Although it is provided with a 2.0 Megapixel camera, it is intended to be a low-cost toy not for professional use. It is powered by a built-in 500 mAh Li-Poli battery. The distance from the motors is 16 cm. Their height from the ground is 4.5 cm. The frame and the blades are made of plastic material. We selected a NT4Contra quadcopter, manufactured by AirVision (Figure 6), as representative professional UAV. It has four pairs of engines with counter-rotating blades. The frame is made of carbon. It is powered by two 4,600 mAh Li-Poli batteries housed in the legs. Below the head there is a dock for a camera (not provided). The distance from the motors is 36 cm. The height of the motors from ground is 22 cm (Figure 3). RCS MEASUREMENTS SYMA quadcopter. SEPTEMBER 2017 AirVision quadcopter. IEEE A&E SYSTEMS MAGAZINE 29