# Dual Cancelled Channel STAP for Target Detection and DOA Estimation in Passive Radar
## 5 Experimental Results  
This section provides an experimental validation of the effectiveness of the AB-STAP scheme for moving target detection and localisation in mobile passive radar. The data are acquired by a multichannel receiver developed by Fraunhofer FHR, mounted on a ground moving vehicle and exploiting DVB-T transmissions (see Figure 7a). The experimental setup and the considered dataset were formerly used in [18], where the full array STAP scheme was successfully applied. In this paper, the full array solution is compared with the AB-STAP approach in order to verify the benefits of the latter in a real scenario. Figure 6: Comparison of DOA estimation accuracy as a function of the amount of training data. Target input SNR was set to \(-45\) dB and bistatic velocity to \(7\) m/s. Figure 7: **(a)** The experimental radar system installed behind a vehicle in side-looking. **(b)** The ultralight aircraft (Delphin). The campaign was carried out in a rural area in western Germany. The selected illuminator of opportunity was the Eifel DVB-T transmitter. The receiver configuration consisted of two PARASOL units [36], each providing two receiving channels. The four available channels were displaced in the along-track direction to form a side-looking ULA. An absorbing material was used to attenuate possible back lobe returns. The available channels were all employed as surveillance channels, while the reference signal was reconstructed by resorting to a decode/recode strategy. Figure 8 shows a sketch of the bistatic acquisition geometry. The transmitter was in a direction approximately opposite to the observed scene. An ultralight aircraft (Delphin) was employed as a cooperative target during the acquisition campaign (see Figure 7b). In addition to the real target, four simulated moving targets were injected into the acquired data. The parameters of the real and simulated targets are reported in Table 2.  
It is worth noting that the same strategy presented in [18] for calibration of the spatial steering vector component was adopted here in order to mitigate the impact of the potential angle-dependent inter-channel imbalance on the target detection and localisation performance. Specifically, this was applied to vector \(\mathbf{s}\) in the full array STAP scheme and equivalently to vectors \(\mathbf{s}_{A}\) and \(\mathbf{s}_{B}\) in the AB-STAP scheme. Figure 9 reports the range-Doppler maps resulting from a CPI of \(\approx 0.57\) s (corresponding to 512 OFDM symbols of the DVB-T signal). In particular, Figure 9a shows the map resulting from a single channel, namely, before STAP, normalised to the noise power level. Given a platform velocity of 13.8 m/s and a carrier wavelength of 0.43 m, the stationary scene echoes appeared to spread over a Doppler bandwidth of approximately 64 Hz. The radial velocities and DOAs of the real and simulated moving targets were such that they fell within Doppler bandwidth of clutter, being mostly buried into it and therefore not easily detectable. Notice the average SCRN values were higher compared with those of the simulated case, since targets compete with a lower local clutter power. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Delphin** & **T1** & **T2** & **T3** & **T4** \\ \hline \(R_{b}\) & \(6596\) m & \(4700\) m & \(3600\) m & \(6850\) m & \(2400\) m \\ \(v_{b}\) & \(-24.5\) m/s & \(-6\) m/s & \(6\) m/s & \(11\) m/s & \(7\) m/s \\ \(\phi_{t}\) & \(\approx 37^{\circ}\) & \(37^{\circ}\) & \(157^{\circ}\) & \(109^{\circ}\) & \(70^{\circ}\) \\ \(f_{D}\) & \(-31.1\) Hz & \(11.7\) Hz & \(-14.9\) Hz & \(15.9\) Hz & \(26.7\) Hz \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Parameters of the real and simulated moving targets. Figure 8: Optical image of the acquisition area. The position and direction of motion of the receiver and the aerial target are indicated with yellow and white arrows, respectively. Red arrow indicates the transmitter direction of arrival. Dashed lines represent the bistatic iso-range curves.