## 4 Test Setup for Experimental Measurements
### Radar System Specifications
LPF 2 has a much lower cutoff frequency of 100 kHz and is designed to suppress unwanted noise components. It also maintains a low insertion loss of less than 0.3 dB within the micro-Doppler baseband range. The filtered I and Q signals are then captured using an Analog-to-Digital Converter (ADC) via a two-channel TRS AUX cable. These baseband radar signals are recorded using the Audacity software on a Raspberry Pi for further processing. The system can be powered either by a 12 V battery or a wall adapter. The down-converted and filtered in-phase (I) and quadrature (Q) signals are captured and processed through an Analog-to-Digital Converter (ADC) by a two-channel TRS AUX cable for recording the baseband radar signals through Audacity(version 3.1) audio editor and recording program in a Raspberry Pi computer. Relevant overall specifications of the system are provided in Table 2.  
Audacity(r) is a free, open-source audio recording and editing software. The software takes up a very small amount of CPU, which was deemed perfectly suited for the Raspberry Pi's computing power. Audacity(r) allows for two-channel recording. Since the I/Q radar signal was recorded through a two-channel AUX cable after filtering and the ADC, Audacity(r) was able to record the frequency information successfully. The vehicles tested are listed in Table 3. All experiments were conducted in an outdoor parking lot on a clear summer day. Measurements were made on a day with minimal wind and in a parking lot clearly away from other vehicles and other objects such as trees. Moreover, we ensured that the radar beam spot was fully contained on the chassis of the vehicle. The radar system was positioned 1.52 m (5 ft) away from each vehicle and at a height of 0.91 m (3 ft), remaining stationary throughout each recording. Both antennas were aligned with zero degrees elevation and azimuth. A photograph of the experimental setup is shown in Figure 6. \begin{table}
\begin{tabular}{c c} \hline
**Specification** & **Value** \\ \hline operating frequency & 10 GHz nom. \\ RF power output & +24 dBm min. \\ front-end noise figure & 1.7 dB max. \\ antenna gain & 16 dB nom. \\ antenna 3-dB beamwidth & 28\({}^{\circ}\) typ. E-plane \\ antenna polarization & 26\({}^{\circ}\) typ. H-plane \\ random access memory & linear \\ Wi-Fi and Bluetooth & 8 GB \\ display & touchscreen, external monitor (connect to micro-HDMI), \\ DC power consumption & and VNC remote connection \\ power supply requirements & 7.25 W max. \\ size & battery (6000 mA/h, 14.8 V) \\ laptop & wall-adapter (6A 15V AC) \\ \hline \end{tabular}
\end{table} 
Table 2: Radar system specifications. \begin{table}
\begin{tabular}{c c c} \hline
**Model** & **Engine** & **Type** \\ \hline
2012 Ford Fusion & 2.5 L 4-cycl 6-speed auto & sedan \\
2015 Kia Forte5 SX & 1.6 L 4-cycl turbo 6-speed auto & hatchback \\
2016 Jeep Compass & 2.4 L 4-cycl 6-speed auto & compact SUV \\
2012 GMC Acadia & 3.6 L 6-cycl (V6) 6-speed auto & SUV \\ \hline \end{tabular}
\end{table} 
Table 3: List of vehicles tested. Measurements were performed under clear sky conditions. Although the temperature and relative humidity (RH) were not recorded during the measurements, these were obtained for the two measurement days (26 and 27 July 2023) from National Weather Service weather reports at the experiment starting times. These values were as follows:  
26 July: 30 \({}^{\circ}\)C and 46.5% RH  
27 July: 31 \({}^{\circ}\)C and 53.1% RH