# Review and Simulation of Counter-UAS Sensors for Unmanned Traffic Management
## 2 Review of the State-of-the-Art Technology
### Active Detection Radars
The detection results of this system show that the detection of the SDR platform if successfully performed in real-time operations, so it can be used for air safety applications by detecting and warning of the threat UAVs. An example of mmWave Radar with a precise detection and 3D localization system for drones can be observed in [10]. The positions of drones are estimated from spatial heatmaps of the received radar signals, obtained by applying a super-resolution algorithm. These positions are improved analyzing the micro-Doppler effect, which is generated by the rotating propellers. This radar presents a novel Gaussian Process Regression model to compensate for systematic biases in the radar data. Finally, another way of detecting UAVs using radars is by means of the Multistatic Forward Scattering Radar (FSR) [11]. The most important principle of a FSR for target detection is the use of the shadow field. When the diffraction angle, which is the angle between the direction of the transmitter-target and the direction of the target-receiver, is approximately zero, the shadow field can be observed at the receiving point. This shadow field is considered in narrow regions where the diffraction angle is approximately zero, causing the forward scatter radar section to increase considerably compared to monostatic radar sections, which occurs only when the size of the target is larger than the wavelength. In the multistatic configuration of a FSR, a certain number of transmitting and receiving positions in the air and receiving positions on the ground must be used. The altitude of the targets must always be equal to or less than the altitude of the airborne transmitter positions, which could be placed onboard UAVs or any other type of aircraft. This kind of airborne sensor network is described here for completeness, but we do not model it in the second part of the paper. To summarize, the highest disadvantage of active radars is the need for specially designed transmitters that can be difficult to deploy. Next, we detail some commercial active radars. The ART Midrange 3D [12] is a high-resolution C-UAS FMCW surveillance radar. This high-performance sensor is specifically designed to detect small unmanned aerial vehicles (C-UAS) and for its use in unmanned aerial vehicles. The detection of the radar is based on the detection of the radar, which is a multi-mode, and the detection of the radar is based on the detection of the radar. The detection of the radar is based on the detection of the radar, which is a multi-mode, and the detection of the radar is based on the detection of the radar. aircraft traffic management (UTM). The radar is composed of a 3D multibeam antenna system and a high-power amplification stage and is capable of detecting, tracking, and classifying micro quadcopters and micro fixed-wing UAVs, with extended elevation coverage. The main specifications of this solution can be seen in Table 1.  
Another commercial solution, provided by Indra [13], called ARMS, includes another FMCW radar. Its main characteristics are detailed next, in Table 2.  
German company HENSOLDT has developed a drone detection system called Xpeller Counter UAV solution [14]. This solution can detect the potential threat through a radar system whose specifications can be seen in Table 3 (two different radar systems may be integrated). Meanwhile, Echodyne [15] has developed an alternative active radar solution based on an Electronic Scan Antenna capable of simultaneously tracking (with very high detection \begin{table}
\begin{tabular}{c c} \hline \hline
**Specification** & **Value** \\ \hline Frequency Band & Ku-band \\ Bandwidth & 1 GHz \\ Elevation Control & +/\(-\)5 degrees \\ Instrumental Detection Range & 5000 m \\ Coverage Area & 78 km\({}^{2}\) \\ Azimuth Coverage & 360\({}^{\circ}\) \\ Scan Rate & 60 rpm (configurable) \\ Range Resolution & 1 m-0.2 m \\ Range Accuracy & 0.25 m–0.05 m \\ Communications & TCP/IP over Ethernet \\ Protocol & XML-based on NMEA0183 \\ \hline \hline \end{tabular}
\end{table}