# Target Detection of Passive Bistatic Radar under the Condition of Impure Reference Signal
## 3 Proposed Target Detection Method under the Condition of Impure Reference Signal
### Target Detection Method Based on Impure Reference Signal
Firstly, the ECA is performed to obtain the weights of the clutter suppression of the two methods, and the amplitudes of the weights of the proposed method are presented in detail in Table 4. As is shown, within the range cells where the clutter actually appears, such as in cells 1, 10, and 25, the corresponding weight values will have obvious peaks, while those corresponding to the other range cells are very small, which is consistent with the previous analysis. The core reason for this phenomenon is that clutter plays a major role due to the orthogonality between targets and the reference signal subspace. Then, the detection results of the two methods for target 1 and target 2 are depicted in Figures 6 and 7, respectively. By comparison, it can be found that exploiting the proposed method for target detection can effectively overcome the problems of weakening target energy and generating false targets occurring in the conventional detection method. Next, the detection results of target 3 using the two methods are given in Figure 8. Clearly, target 3 existed only in the

Figure 4: RDCC results of traditional target detection in pure case and impure case: (**a**) results of pure case; (**b**) results of impure case. Figure 5: Detection results of traditional target detection in pure case and impure case: (**a**) results of pure case; (**b**) results of impure case. surveillance signal and is insensitive to whether the reference signal is disturbed by other targets or not; at the same time, the proposed method will not have any negative impact on the detection of target 3. Moreover, Figure 9 shows an overall comparison of the detection results obtained by using the proposed method and the traditional method to process the impure reference signal. It is easy to observe that the proposed method effectively purifies the reference signal and achieves cleaner target detection results. Finally, based on Matlab2020b and Intel i5 CPU processors, the execution efficiency of the two methods is compared in Figure 10. It can be seen that the execution efficiency of the proposed method is lower than that of the traditional method. The main reason for this problem is that the proposed method regards the detection results of the traditional method as feedback information, and on this basis, signal recognition and reconstruction are added successively, thus reducing the computational efficiency. Furthermore, according to the flowchart of the proposed method in Figure 2, the proposed method is divided into three modules: one is the feedback module, another is the detection module, and the last one is the reference signal purification module. Table 5 provides the running time and proportion of time each module takes up in the proposed method. It is evident that the main computational cost of the proposed method lies in the feedback and detection modules. These two modules process different data, but the methods are the same, allowing them to be accelerated through parallel computing. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Range Cell** & \multicolumn{8}{c}{**Amplitudes (Rounded Results)**} \\ \hline
1–10 & 0.276 & 0.000 & 0.000 & 0.001 & 0.002 & 0.002 & 0.002 & 0.002 & 0.002 & 0.274 \\
1–20 & 0.003 & 0.003 & 0.003 & 0.003



Although the foregoing contents demonstrate the effectiveness of the proposed method in dealing with the problem of the impure reference signal, it is undeniable that the proposed method still has certain limitations. Firstly, for multiple targets with the same velocity, such as grouped targets, the tracks of these targets may fall into the same Doppler cell, causing interference in distinguishing real and false targets, thereby rendering the proposed method ineffective. Secondly, the proposed method is not applicable in cases where the surveillance channel is far from the reference channel--for example, when the surveillance channel and the reference channel are deployed back-to-back.