# Dual Cancelled Channel STAP for Target Detection and DOA Estimation in Passive Radar
## 4 Performance Analysis in Simulated Scenarios  
In this section, we analyse the effectiveness of the AB-STAP approach for a multichannel mobile passive radar, and we compare its performance with respect to the corresponding full array solution in terms of target detection and DOA estimation capability. To this purpose, we tested the considered schemes against a simulated clutter scenario.  
We considered the case of a side-looking airborne receiver exploiting a DVB-T transmitter as illuminator of opportunity. Starting from a simulated reference signal, the clutter returns were generated, assuming a distribution of stationary and independent scatterers according to the model in [10]. Table 1 summarises the main simulation parameters.  
A clutter-to-noise ratio (CNR) of 20 dB was set at the input of each channel before range compression. Two identical moving targets were simulated at bistatic range \(R_{b}=2\) km and 5 km, having DOA \(\phi_{t}=90^{\circ}\), bistatic radial velocity \(v_{b}=8\) m/s (\(f_{D}\cong 18\) Hz), and signal-to-noise power ratio (SNR) \(-50\) dB at the input of each channel.  
In Figure 2(a), the range-Doppler map obtained from a single channel is reported. As is evident, the non-negligible receiver altitude caused a non-uniform distribution of clutter in the near range region, where the first target was located. In contrast, in the far range region of the second target, clutter distribution was uniform, spreading over a Doppler bandwidth of approximately \(2v_{p}/\lambda\cong 60\)\(Hz\). The resulting target SCNR after range compression and Doppler processing was \(-27\) dB and \(-26\) dB, respectively, so that both targets were completely buried into clutter returns. The SCNR was measured as the ratio between the power level at the target range-Doppler location, when the processing was fed only with the target echo, and the disturbance power level estimated on the area surrounding target location, when only clutter and noise were present.  
Figure 2(b) shows the range-Doppler map obtained when applying the full array STAP scheme, using \(N=4\) channels, \(L=3\) adjacent Doppler bins, and \(K=2 NL=24\) training data. The clutter was effectively cancelled, and the SCNR of the target at far range was brought to 16 dB, with an improvement of 42 dB. For the near range target instead, the achievable SCNR was limited to 12 dB, due to the inhomogeneity of clutter data. To avoid this, in Figure 2(c), the sample support was reduced to \(K=16\). In this case, however, the small number of training data yielded higher adaptivity losses, rising the residual disturbance background and limiting the final SCNR to 8 dB for both targets.  
The result obtained when applying the AB-STAP scheme with \(K=16\) training data is shown in Figure 2(d). The array was split into two non-overlapped sub-arrays of \(N_{0}=2\) antennas, forming the A and B channels. With \(N=4\) elements at disposal, this choice ensured the largest phase centre displacement. In this case, the clutter was still effectively  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Values** \\ \hline Receiver altitude & 1000 m \\ Receiver velocity & 13 m/s \\ Carrier frequency & 690 MHz \\ Bandwidth & 7.61 MHz \\ CPI duration & \(\approx\)0.57 s \\ Number of channels & 4 \\ Element spacing & \(\lambda/2\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Parameters of the simulated scenario.  
Figure 2: Range-Doppler maps from the simulated clutter scenario: (**a**) single channel; (**b**) after full array STAP with \(K=24\) training data; (**c**) after full array STAP with \(K=16\) training data; (**d**) after AB-STAP with \(K=16\) training data.  
suppressed, and the limited number of secondary data counteracted the effect of non-homogeneous clutter at near range, without introducing undesirable adaptivity losses. As a result, a final SCNR of 15 dB was obtained for both the far and the near range targets.