# Car Bumper Effects in ADAS Sensors at Automotive Radar Frequencies
## 4 Experimental Setup and Procedure
### Measurement Setup  
Figure 3 shows a diagram of the measurement setup. The measurement equipment is highlighted in orange and the antennas are represented by yellow triangles. The green lines correspond to the Ethernet cables, and the yellow lines depict coaxial cables. The anechoic chamber is sketched in blue, and the holder with the material is visible as a purple line between the two antennas. The measurement equipment is connected via a network switch to a laptop to enable remote control. We used a Rohde & Schwarz SMB100A microwave signal generator to create the transmitted signal at an intermediate frequency. This signal feeds a Rohde & Schwarz SMZ110 frequency multiplier whose output is in the desired radar frequency range. As the frequency multiplier can be connected to the signal generator via the USB, both devices can be configured as one single device. This indicates that we can directly switch the signal generator to the frequency we need at the output of the multiplier. A Rohde & Schwarz FSW85 signal and spectrum analyzer, operating in the range from 2 Hz to 85 GHz, was the core equipment at the receiver side. Two directional standard gain horn antennas with a gain of 20 dBi completed the setup at both the transmitter and receiver ends. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{**Plastic Type**} & \multirow{2}{*}{**Type of**} & \multirow{2}{*}{**Color**} & **Primer** & **Base** & **Varnish** & **Sample Size** \\  & & & **Thickness** & **Thickness** & **Thickness** & **Thickness** & **W (cm) \(\times\) L** \\  & & & **(\(\mu\)m)** & **(\(\mu\)m)** & **(\(\mu\)m)** & **(cm)** \\ \hline A & PP and PE & No paint & FXT & – & – & – & 21.9 \(\times\) 29.8 \\ B & PP and PE & Three layer & N9 blanc nacre & 2–3 & 27–29 & 35–37 & 21.9 \(\times\) 30.4 \\ C & PP and PE & Double layer & 9V noir pearl black & 2–3 & 12–14 & 31–33 & 23.3 \(\times\) 30.5 \\ D & & Double layer & VH rouge elixir & 2–3 & 19–21 & 39–41 & 21.6 \(\times\) 29.9 \\ E & copolymer + talc & Double layer & F4 intense grey & 2–3 & 12–14 & 41–43 & 21 \(\times\) 31 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Composition of the car bumper samples analyzed. Figure 3: Diagram of the measurement setup. The antennas and the multiplier were placed inside an anechoic chamber [32], as shown in Figure 4, while the rest of the equipment remained outside. The backside of the antennas and the entire multiplier were covered with absorbers to avoid undesired reflections. For clarity, the absorbing material around the antennas and the frequency multiplier were removed when taking the pictures. The absorbers used in the chamber were Eccosorb VHP-2 from Emerson & Cuming, which can be used at 3 GHz. The manufacturer provided data up to 110 GHz, which is the attenuation in the automotive radar frequency band of around \(-55\) dB. The temperature during the measurements is always controlled to be in the range of \(21\pm 1\,^{\circ}\)C to limit its influence on the uncertainty of the measurements [33]. The sample holder consisted of a flat panel of wood with a rectangular hole in the center, sizing 20.7 cm by 20.7 cm. The holder with the sample was placed halfway between the two antennas, at a 53 cm distance from each other, meeting the far-field condition of the antennas (15 cm at the highest frequency of the band under study, considering the size of the antennas used. It reached both lateral walls, ceiling and floor of the chamber, thus dividing the anechoic volume into two areas. The hole size was chosen so that the radius of the area illuminated by the 3 dB beam width of the antennas had its footprint inside the bumper sample at the selected measurement distance. The center of the hole was aligned with the antenna centers. The bumper samples were attached to the holder on the reception side using four screws and two plastic bands (see Figure 5). For its part, the holder was coated with an absorber on the transmitting side to ensure that the signal received was only passing through the bumper sample.