# Synchronization of Monostatic Radar Using a Time-Delayed Chaos-Based FM Waveform
## 8 Conclusions and Perspectives  
The recent interest in chaos opens more trends to develop different secure applications in radar communication systems. Indeed, the key issue for modern military and civil radars still depends on how to let the radar exhibit more robustness over a wide-band noise. In this paper, to overcome the problems encountered in VLF and other VHF radar systems, such as radar size, large transmission energy, and less precision in range resolution, we developed a new 0.3 GHz indirect mono-static FM-based chaotic system which is based on a time-delay chaotic system. Here, the main contribution is to utilize the Phase-Locked Loop (PLL) for the synchronization process in this radar in order to detect the target's echo \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Type of Direct Radar** & \begin{tabular}{c} **SNR** \\ **Range** \\ \end{tabular} & **Synch. Type** & \begin{tabular}{c} **Parameters** \\ **Mode** \\ \end{tabular} & **Bandwidth** \\ \hline \begin{tabular}{c} Based on Colpitts \\ Oscillator [8] \\ \end{tabular} & \(-20\) dB & Error Feedback & Match & \begin{tabular}{c} Wide-band \\ (\(f>1.6\) GHz) \\ \end{tabular} \\ \hline \begin{tabular}{c} Based on Time-Delay \\ Feedback [2] \\ \end{tabular} & \(-60\) dB & Adaptive Observer & Match and & Broadband \\ \
\begin{tabular}{c} Feedback [2] \\ \end{tabular} & \(-50\) dB & Pecora and Carroll (PC) & Mismatch &
\begin{tabular}{c} Broadband \\ (\(f<3\) kHz) \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: A comparison example of the direct Chaotic Radars. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Indirect Radar** & **SNR Range** & **Synch. Type** & **Bandwidth** & **Simulation** \\ \hline \multirow{3}{*}{\begin{tabular}{c} Lorenz-Based Radar \\ (Bistatic Radar) \\ \end{tabular} } & \multirow{3}{*}{\(6\) dB} & Pecora \& Carroll & Wide-band \\  & & & (PC) (complete) & \(f_{c}=2.5\) GHz, [9] \\ \cline{2-5}  & & & & \(f_{\mathrm{s}}=10\) GHz, [10] \\ \cline{2-5}  & & & & \(B.W=500\) MHz [13] & System (ADS) \\ \hline \multirow{3}{*}{\
\begin{tabular}{c} Proposed \\ Time-Delayed \\ Feedback \\ (Monostatic Radar) \\ \end{tabular} } & \multirow{3}{*}{\(-15\) dB} & \multirow{3}{*}{
\begin{tabular}{c} Phase Locked \\ Loop (PLL) \\ \end{tabular} } & Wide-band \\  & & & \(f_{\mathrm{c}}=0.3\) GHz & MATLAB \\ \cline{1-1} \cline{3-5}  & & & \(f_{\mathrm{s}}=5\) GHz & Simulink \\ \cline{1-1} \cline{3-5}  & & & \(B.W=150\) MHz & \\ \hline \end{tabular}
\end{table} 
Table 2: A comparison of indirect FM Chaotic Radars when a time-delay feedback radar with echo delay = 2 ns. signal accurately under different noise levels and with less design complexity. Thus, the loop gain (G) is carefully set when utilizing PLL in this model. This means that the system has been successfully designed with no need to utilize any complete self-synchronization or complex projective synchronization such as adaptive observer to correctly recover the echo signal. Nevertheless, the effect of sampling interval (in ns) utilized in designing this system begets some restrictions on the signal processing during the simulation process. Therefore, the simulation stop time is set at 0.01 s for proper operation, and hence the robust indirect chaotic radar can be implemented. As a result, such a radar system is considered as one of the state-of-the-art models to detect the target over a high noisy environment and less degradation in the recovered echo signal. Upon these results, this work can identify some aspects for further study, as follows: (i) The Doppler effect of the echo signal needs more intensive investigation using ambiguity function for moving targets. (ii) To provide a high range resolution, the indirect chaotic radar based on FM can be developed to operate in wider microwave bands (e.g., beyond 1 GHz-3 GHz). Moreover, the different hyperchaotic systems may be also suggested to design monostatic/bi-static radar systems using FPGA.