# Fingerprints of the Automotive Radar Scattering of Passenger Cars and Vans
## 3 Results and Discussion
### Scattering Characteristics of Different Vehicle Types  
This section examines, whether the underbody detections enable a radar-based fingerprinting of different vehicle types. First, the spatial distribution of the target detections as well as their RCS values were analyzed for each vehicle. Due to the limited sensor resolution, multiple scattering centers can fall into the same range bin. Therefore, it is not possible to associate every accumulation of detections unambiguously with a specific part of the vehicle. Nevertheless, the detection density can be used to identify regions with high reflectivity. In addition, the RCS values can be used to compare the reflectivity of the different underbodies. In Figure 8, the spatial distribution of target detections as well as their RCS values are illustrated for the six different vehicles. As expected, the highest detection densities were located at the rear bumper at \(x\,=\,0\,\mathrm{m}\) with RCS values between \(10\,\mathrm{dBsm}\) and \(30\,\mathrm{dBsm}\). All vehicle types showed a similar formation of detections at distances between \(x\,=\,1\,\mathrm{m}\) and \(x\,=\,1.5\,\mathrm{m}\). As evaluated in Section 3.1, these detections were caused by a superposition of backscatter from the underbody, the tailpipes, the C/D-pillar and the roof. The fact that the detection densities and RCS values of the S-Class and the GLS were similar in this region supports the assumption that the C/D-pillar and the roof are of minor influence since the D-pillar of the GLS is located in the same range cell as the rear bumper. The RCS values in the same region, for the EQE, were approximately \(5\,\mathrm{dBsm}\) lower, which is attributed to the non-existent tailpipes and exhaust pipes. For the G-Class, the V-Class and the Sprinter, the accumulation of detections between \(x\,=\,1\,\mathrm{m}\) and \(x\,=\,1.5\,\mathrm{m}\) were concentrated in a smaller area and had approximately \(10\,\mathrm{dBsm}\) larger RCS values compared to the S-Class and the GLS. These increased RCS values are consistent with the fact that the rear axle, wheel suspensions and chassis frames are clearly visible and cause stronger backscatter. In the front part of the vehicles, further significant differences are visible: While the detections for the S-Class were distributed over the entire bounding box, the GLS showed two point clouds at \(x\,=\,2.9\,\mathrm{m}\) and \(x\,=\,3.9\,\mathrm{m}\). The detections at \(x\,=\,2.9\,\mathrm{m}\) were concentrated in a small area and had slightly increased RCS values up to \(0\,\mathrm{dBsm}\), which is significantly higher compared to the detections at the same distance for the S-Class. These detections seem to stem from the exhaust system, as they are located in an area of exhaust pipes and catalytic converters. For the EQE, only two minor accumulations of detections were located at \(x\,=\,3\,\mathrm{m}\) and \(x\,=\,3.8\,\mathrm{m}\), which were probably caused by the left side mirror and the right front wheel. It seems as if the flat underbody without any prominent geometries leads to reduced backscatter and therefore fewer target detections. For the G-Class, a very high density of detections was seen at \(x\,=\,3.4\,\mathrm{m}\) with RCS values up to \(15\,\mathrm{dBsm}\). These detections may probably be caused by the side of a horizontal metal plate below the front axle, which is a few centimeters lower than the rest of the underbody. The detections for the V-Class were distributed more evenly compared to the G-Class. Two regions with  
Figure 7: Arithmetic mean number of target detections for the measurement setups using microwave absorbers around fixed distances \(R\). slightly higher detection densities and increased RCS values can be seen at \(x~{}=~{}2.4\) m and \(x~{}=~{}4.2\) m. However, due to the limited sensor resolution, it remains uncertain if these can be associated with specific underbody parts.