Unmanned vehicles, such as UAVs (unmanned aerial vehicles), UGVs (unmanned ground vehicles) and AUVs (autonomous underwater vehicles) transmit and receive a variety of signals. These signals may include GPS/GNSS signals, telemetry and sensor data, and cellular and wifi communication signals that allow the vehicle to form part of a network or connect to the Internet of Things (IoT).
The unmanned vehicle may communicate with a ground station, satellite or another vehicle and will require an antenna – a transducer that converts electrical energy into electromagnetic waves and/or vice versa – to transmit and receive signals. With advances in modern materials, antennas for UAVs can be constructed with a smaller size and embedded into the aircraft with a low profile, resulting in less weight and less aerodynamic drag on the aircraft.
Antennas are tuned to specific frequencies or frequency ranges, and can be either linearly or circularly polarized. Linearly polarized antennas can be simpler to construct and may provide greater range. However, due to the need to keep transmitting and receiving, antennas are aligned to ensure maximum signal overlap, which can make them unsuitable for fast-moving unmanned aircraft, which might change direction frequently and thus bring the antennas out of alignment.
Circularly polarised antennas are more suitable for fast-moving vehicles as the radiation pattern ensures that there is some overlap no matter the angle of antenna alignment.
Antennas can also be classified as directional or omni-directional. Directional antennas can achieve greater range at the cost of coverage, whereas omni-directional antennas provide coverage 360 degrees horizontally from the antenna but are limited in range. Some unmanned vehicle control stations may incorporate both types of antenna, monitoring the signal reception and switching antennas as needed.
Most unmanned vehicle communications signals will occur in the radio frequency range, however due to increasingly crowded airwaves, microwave communications are becoming more common. Microwave signals provide greater bandwidth than radio signals but cannot be refracted in the way that radio frequency signals can, thus limiting them to line of sight (LOS) applications.