# Analysis on Target Detection and Classification in LTE Based Passive Forward Scattering Radar
## 2 Target Detection in Passive Forward Scattering Radar
### Passive Forward Scatter Radar Cross Section  
The target's RCS of a real model was first estimated by using Computer Simulation Technology (CST) Microwave studio software for different vehicle shapes, sizes and also plane wave angles of incident, \(\phi\). In theory, the RCS depends on the target's physical geometry and exterior features, the direction of the illuminating radar, the bistatic angle, \(\beta\), the radar transmitter frequency and the types of material used. Two wave incident angles (\(\phi=59^{\circ}\) and \(\phi=90^{\circ}\)) were analyzed, which follows the experimental setup and geometrical scenario as illustrated in Figures 1 and 2 respectively.  
The Cartesian and polar plots of vehicle's RCS were analyzed in order to examine the effect of incident angle to the RCS in passive FSR. The models of the vehicles were designed in Autodesk software based on the actual dimensions of the vehicles. As an example, in  
Figure 1: Topology of passive forward scatter radar setup showing wave incident angle, \(\phi\).  
Figure 2: Aerial photo of geometrical experimental site showing LTE base station.  
of the Small SUV is L = 4420 mm, W = 1695 mm, H = 1740 mm as shown in Figure 3. These models were then exported to the CST for simulation and the plane wave from LTE base station is used as the radar signal's source. The RCS was calculated for the 2.6 GHz LTE carrier frequency and angles of incident plane wave, \(\phi\) at 59\({}^{\circ}\) and 90\({}^{\circ}\) as shown in Figure 4.  
The influence of the cross sectional shape and the size of the vehicles on the RCS are presented in the RCS radiation pattern for all bistatic angles at the LTE carrier frequency of 2.6 GHz. The results were analyzed in the form of polar and Cartesian plots as shown in Figure 5. The RCS attributes for the Small SUV at two incident angles are compared in Table 1. The figure and table point out that the amplitude of RCS when \(\phi\) = 90\({}^{\circ}\) is higher than \(\phi\) = 59\({}^{\circ}\), and can be seen at the main lobe magnitude. Moreover, this result explains that the vehicles more likely to be detected at an incident angle, \(\phi\) = 90\({}^{\circ}\). The side lobe level of \(\phi\) = 90\({}^{\circ}\) is smaller compared to \(\phi\) = 59\({}^{\circ}\), which highly fluctuated. This could be the fact that the target's silhouette of the vehicle is much more visible at \(\phi\) = 90\({}^{\circ}\). However, regardless of the angle of the incident wave, the RCS is always maximum at FSR (\(\beta\) = 180\({}^{\circ}\)). This is the main advantage of using forward scattering mode in passive radar where the effects on enhanced RCS can be seen [20].  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multicolumn{2}{c}{**Incident Angle, \(\phi\)**} \\ \cline{2-3}  & **59\({}^{\circ}\)** & **90\({}^{\circ}\)** \\ \hline \multicolumn{1}{c}{Bistatic angle, \(\beta\) of Max RCS (\({}^{\circ}\))} & 180.00 & 180.00 \\ \multicolumn{1}{c}{Max RCS magnitude (dBm\({}^{2}\))} & 60.04 & 62.75 \\ \multicolumn{1}{c}{Side lobe level (dB)} & \(-\)31.30 & \(-\)23.50 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Small SUV RCS values for different incident angles, \(\phi\).  
Figure 4: Radar source towards target at incident angle, \(\phi\) at (a) 59\({}^{\circ}\) and (b) 90\({}^{\circ}\).  
Figure 3: Model of a Small SUV for RCS calculation.