## 3 Results and Discussion
### Parallelepiped  
The sample has the following parameters. Sample size: 0.08 \(\times\) 0.06 \(\times\) 0.04 m, minimum frequency 0.025 m, and maximum 0.017 m attributable to a satellite 2.4 m high at 12 GHz and one of 3.5 at 18 GHz. Three configurations were considered. The first, satellite in a vertical position; the second, satellite in a horizontal position and rotating around the vertical axis; the third, satellite in a precession, according to a 45\({}^{\circ}\) cone with respect to the vertical axis. In this configuration, the 0\({}^{\circ}\) angle is the one in which the satellite is perpendicular to the incident wave. The positions 45\({}^{\circ}\), 225\({}^{\circ}\), 270\({}^{\circ}\), 180\({}^{\circ}\), and 225\({}^{\circ}\) were considered with an anticlockwise rotation of 45\({}^{\circ}\) around the longitudinal satellite axis. In Figure 6, the positioning of the sample is shown; in Figure 7, the reflectivity plots are depicted. In this case, the maximum reflection occurs in the configurations in horizontal rotation, which exposes a greater surface to the signal; the maximum reflection occurs for the 90\({}^{\circ}\) configuration, followed by the 45\({}^{\circ}\) and the 0\({}^{\circ}\) configuration. The vertical configuration also reflects the signal well. It can be seen that the shape of the curves is absolutely unchanged, with an almost constant frequency response. In the configurations of the samples in precession, the only one that shows a non-reflective behavior in all frequencies is 1, with 225\({}^{\circ}\) of rotation around the precession axis, in which the signal is reflected in all directions except toward the receiving antenna. In the others, it can be seen how configuration 5, at 135\({}^{\circ}\) of rotation around the precession axis, is the one that manages to reflect the signal in all frequencies, with peaks between 5 and 6 dB, at regular intervals, at frequencies 13.8, 15.5 and 17 GHz. At 15 GHz, there is the minimum, where there is no reflection. It will thus be possible to understand when the satellite will be in this configuration by associating an optical detection system. Configuration 3, at 270\({}^{\circ}\) of rotation around the precession axis, also has frequencies in which it is possible to identify its position, as well as 2 and 0 (180\({}^{\circ}\) and 45\({}^{\circ}\)). Respectively, this occurs at frequencies between 12.4 and 14 GHz (3), between 15.5 and 16.3, and at 18 GHz (2), at 12.9, and between 14.0 and 14.4 GHz (0). Configuration 4, 225\({}^{\circ}\) of rotation around the precession axis with 45\({}^{\circ}\) rotation around the longitudinal axis of the satellite, has suitable reflection only at 12.4 GHz. Figure 6: Parallelepiped positioning in respect to wave incidence direction. (**a**) Horizontal and vertical positions; (**b**) precession positions. The experimental results show that scaled objects in the 90\({}^{\circ}\), 45\({}^{\circ}\), and 0\({}^{\circ}\) attitude positions, with the dimensions, range aforementioned, are visible with a 400 MHz radar system. Considering the precession positions where the objects better reflect the incident waves, it can be assumed that the corresponding scaled object of 3.5 m will be visible only in some positions when a 400 MHz radar signal is tracking it: it will be visible for all the horizontal and vertical positions and for Precession 2, Precession 3 and Precession 5 positions. Considering the differences in the reflected values, the different positions can be clearly found. Considering the 18 GHz frequency (3.5 m scaled object), the reflection signal related to the relative attitude positions can be highlighted in Figure 8, where both planar positions and precession positions are shown. The great visibility of the object can be noted when it is placed in horizontal positions and rotation, while, when in precession, it appears clear that the visibility strongly depends on the relative position.