## 6 Validation in a Semi-Urban Bistatic Radar Scenario
### Array Signal Processing Performance Evaluation
#### 6.2.2 Second Array Signal Processing Stage: Target DoA Estimation  
The \((m,p)\) coordinates in the CAF domain of each declared target are supplied to the second array signal processing stage to estimate their azimuths. The DoA estimation is carried out in a new beam-space with better accuracy (steering angle increment of 0.01\({}^{\circ}\)) and better resolution, using beamforming weights calculated for maximizing the directivity. Figure 21 depicts the radiation patterns with a maximum radiating axis towards the broadside, for the NULA with weights calculated to maximize the directivity, and weights calculated to control the SLL, showing a narrower main beamwidth for the first one.  
For the \((m,p)\) pair associated with each declared target, a new set of radiation patterns is generated with maximum radiating angles varying from \(-30^{\circ}\)--\(-30^{\circ}\), with a step of 0.01\({}^{\circ}\) (\(\Phi_{DoA}=\{-30^{\circ},-29.99^{\circ}....,29.99^{\circ},30^{\circ}\}\)); the target DoA is estimated as the maximum of the beamformer output spectrum expressed in Equation (16).  
As an example, the detection matrix of the 30 th CPI is presented in Figure 22a. The detections associated with each considered target (\(T1\), \(T2\) and \(T3\)) are marked in yellow. The beamformer output spectrum built for each target detection is shown in Figure 22b. The estimated target azimuth will be the maximum of the associated beamformer output spectrum.  
\begin{table}
\begin{tabular}{c c c c} \hline  & **T1** & **T2** & **T3** \\ \hline Single radiating element & \(1/25\) & \(31/52\) & \(70/80\) \\
**NULA (\(\mathbf{w}_{SLL}\))** & \(\mathbf{15/25}\) & \(\mathbf{45/52}\) & \(\mathbf{80/80}\) \\ NULA (\(\mathbf{w}_{MD}\)) & \(14/25\) & \(43/52\) & \(80/80\) \\ \hline \end{tabular}
\end{table}
Table 11: Number of detections with respect to the number of Coherent Processing Intervals (CPIs) associated with the considered trajectories.  
\begin{table}
\begin{tabular}{c c c c} \hline  & **T1** & **T2** & **T3** \\ \hline Single radiating element & 5.9 dB & 8.9 dB & 13.2 dB \\
**NULA (\(\mathbf{w}_{SLL}\))** & \(\mathbf{9.7}\) dB & \(\mathbf{14.8}\) dB & \(\mathbf{17.2}\) dB \\ NULA (\(\mathbf{w}_{MD}\)) & 9.3 dB & 14.1 dB & 16.9 dB \\ \hline \end{tabular}
\end{table}
Table 12: Signal-to-Interference Ratios (SIR) study for the selected targets.  
Figure 21: Comparison of azimuth radiation patterns of NULA with weights calculated for maximizing the directivity (blue) and for guaranteeing \(SLL<15\) dB (red).  
Figure 23 presents the estimated angles of all of the detections for the three considered trajectories in the acquisition interval. At this point, 3D targets parameter space can be transformed to 2D map coordinates. When the trajectories are depicted in the radar scenario (Figure 24), the target movement dynamics fits well with expected target echoes generated by vehicles running along the Alcala-Meco road and R2 highway, respectively. GPS data are also represented validating the results obtained with the NULA and the two-stage beamformer.  
Figure 23: DoA based on the beamformer output spectrum for targets \(T1\), \(T2\) and \(T3\).  
Figure 22: DoA based on the beamformer output spectrum for detections in the 30 th CPI associated with the considered trajectories.