# Review and Simulation of Counter-UAS Sensors for Unmanned Traffic Management
## 2 Review of the State-of-the-Art Technology
### Passive Detection Radars  
Passive radars do not require a specially designed transmitter. There are two types of passive radar, the single station passive radar, which exploits only one illumination source, and the distributed passive radar, which uses the existing telecommunications infrastructures as illumination sources to enhance the UAV detection. Typically, two different widespread signals are used: cellular systems and the digital video broadcasting systems.  
Passive bistatic radars (PBR) have a challenging problem in the detection of UAVs due to their low RCS [18]. Range migration (RM) occurs in the coherent processing interval, which makes it difficult to increase coherent integration gain and improve radar detection ability, although there are techniques to alleviate this problem. An example of single-station passive radar is the investigation presented in [19], where it is possible to localize small UAVs in 3D by exploiting a passive radar based on Wi-Fi transmissions. A demonstration  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Specification** & **Value** \\ \hline Detection range & 2.5 km \\ Frequency & 24.05–24.25 GHz \\ Field of view & 120\({}^{\circ}\) azimuth \\  & 80\({}^{\circ}\) elevation \\ Angular resolution & 2\({}^{\circ}\) azimuth \\  & 6\({}^{\circ}\) elevation \\ Search while track & object tracks are updated at \(\sim\)10 Hz while \\  & continuously scanning entire field of view \\ Track acquisition rate & \(<\)1 s \\ Max tracks & \(\leq\)20 simultaneous tracks \\ \hline \hline \end{tabular}
\end{table}
Table 4: Echodyne Counter-Drone Radar specifications.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Specification** & **Value** \\ \hline Instrumented range & 7800 m \\ Micro-UAV detection range & 1200 m \\ Mini-UAV detection range & 2100 m \\ Small UAV detection range & 4000 m \\ Minimum detection range & 10 m \\ Scan sector & \(\pm\)45\({}^{\circ}\) (fixed)–360\({}^{\circ}\) with pan/tilt mount \\ Vertical coverage & \(\geq\)40\({}^{\circ}\) \\ Number of simultaneously displayed tracks & Up to 512 \\ Electronic scan rate & 2 Hz or 4 Hz \\ Minimum detection velocity & \(<\)0.1 m/s \\ Range accuracy & \(\pm\)3 m \\ Angular accuracy (azimuth) & \(<\)0.8\({}^{\circ}\) \\ Angular accuracy (elevation) & \(<\)5\({}^{\circ}\) \\ Operating frequency & X-band \\ Connectivity & Ethernet \\ \hline \hline \end{tabular}
\end{table}
Table 5: Ranger R8 SS-3D specifications.  
of the capability of the radar to estimate the position of the target from the ground by exploiting multiple surveillance antennas is performed.  
In the case of distributed passive radar, a possible approach is the one proposed in [20], where the detection system uses reflected global system for mobile communications (GSM) signals to locate and track UAVs. Another example of distributed passive radar is the one presented in [21], where a fixed-wing micro-UAV using passive radar based on digital technology is detected using audio broadcasting signals up to a distance of 1.2 km. The experiment was achieved at a lower frequency of 189 MHz in the VHF band.  
The major disadvantage of passive radar is that a large amount of postprocessing effort or multiple receivers are required to obtain acceptable detection accuracy.