# Comprehensive Review of UAV Detection, Security, and Communication Advancements to Prevent Threats
## 3 Classification of UAVs
### Classification of Drones  
Drone is a very generic term and can refer to intelligent or autonomous vehicles such that there are unmanned aerial vehicles of different types. This can be hexarotors, quadrotors, multirotors or wing-based air vehicles. Mainly discussing the flying drones, they can be classified into three main categories as follows:  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Sr. No.** & **Bandwidth** & **Description** \\ \hline \multirow{4}{*}{1} & \multirow{4}{*}{2.4 KHz to 2483.500 MHz} & The appropriate standard is EN 300 328, which is digital wideband data transmission equipment, and sometimes, the standard used is EN 300 440, which is general short-range devices. \\  & & **Purpose:** Mostly used for short-range surveillance or short-range maneuvering missions. \\  & & Operational power is less or equal to 1 watt, whereas the power spectral density is less the 50 mW\(/\) 1 MHz frequency. The standard is EN 201 893, which is known as RLAN equipment. \\  & & **Purpose:** Long stay in sky operations, used mainly for aerial photography. \\  & & Its operational power rating is less than 25 mW and standard is EN 300 440, which is general short-range devices. \\  & & **Purpose:** Used for short-range surveillance with fast maneuvering and manipulating tasks. \\  & & **This is the frequency used only for the International Telecommunication Union (ITU) and, therefore, cannot be used for communication with drones. \\  & & **Purpose:** Used in such operations where data sharing is important with ground control room (GCR). \\ \hline \hline \end{tabular}
\end{table}
Table 1: Frequencies through which GCR communicates with UAVs.  
Figure 2: Communication channels mostly used to control UAVs.  
* Rotary-wing drones;
* Fixed-wing drones;
* Hybrid-wing drones;
* Flapping-wing drones.  
The drones with a vertical take-off and landing (VTOL) feature and that can hover at a high rate are known as rotary-wing drones. The most common example is a quadrotor unmanned aerial vehicle that has four brushless DC motors. Drones with the capability to fly aggressively and glide even with heavy payloads are known as fixed-wing drones. They perform a horizontal take-off and landing (HTOL). Lastly, the drones that have both fixed and rotary wings are known as hybrid-wing drones. They are designed to have both features of rotary- and fixed-wing drones so that they can perform HTOL and VTOL along with high-rate hovering. Some of the robots are designed to exhibit the flying motion of a fly [18], and here they proposed a 5% more power-efficient wing by changing the wing stiffener pattern parametrically. An experimental aerodynamic analysis found that this could relate to increased wing stiffness, as well as indications of vortex generation during the flap cycle. The experiments reported an improved generated lift, allowing the DelFly to be outfitted with a yaw-rate gyro, pressure sensor, and microprocessor. These flapping-wings were later scaled to the micro level and are known as flapping-wing micro air vehicles (FWMAVs), due to inspiration taken from microscopic insects. These FWMAVs have the ability to perform activities in urban and interior environments. However, there are many hurdles for the successful flight of these vehicles that are replicating insect flight, including their design, manufacture, control, and propulsion [19; 20].