Unmanned Systems Technology 006 | ECA Inspector Mk2 USV | Antenna systems | Northwest UAV NW-44 | Unmanned ground vehicles | Navigation systems | Lunar X challenge

40 Focus | Antenna systems satellite. However, recent developments have reduced the size of the tracking system and minimised the diameter of the array used to less than 15 cm (6 in), although receivers still tend to weigh about 10 kg as they include a low-noise signal block and a tracking mechanism controlled by a GPS receiver and gyroscope. Smaller dishes can be used, as the ‘spot’ beams in the Ku and Ka bands from the current generation of comms satellites are more powerful. Ground control The antenna on an unmanned craft is only half the solution. The height of the antenna on a ground station can have an effect on a UAV’s range as it gives a longer line-of-sight connection. This however presents a challenge in balancing the size and polarisation of the ground antenna with its use on a mast that also rotates to track the aircraft. Ground antennae typically use 30 sectors of 15 º and are steered using the GPS coordinates of the craft, but they have to be designed so that they do not catch the wind and become in effect a sail at heights of up to 5 m. The control centre antenna usually provides the higher gain part of the link and may be a medium-to-high gain omnidirectional, medium-gain sector or a high-gain directional antenna. A directional antenna is likely to need a two-axis steering system, although a less complex but compact multi-sector antenna array can be deployed quickly to provide intermediate range coverage for communicating with a UAV. Antenna systems are also used for very short range data transfer links. These closely coupled links use an antenna on the data electronics to transfer video and other data quickly to a handheld terminal, which avoids having to open up the craft – whether it be a UAV, UGV or submarine system – to access a USB plug to transfer the data via a cable. It also means the electronics can be sealed to prevent moisture or dust from interfering with the sensitive electronics. Conclusion The antenna is a key part of the design of an unmanned system. From the humble dipole used on many UAV craft to the latest electronic metamaterials providing a conformal satellite antenna, the range of technologies is only increasing. Close cooperation between the antenna developer and the system integrator provides the optimum trade- off between range, data rate and weight, depending on how the unmanned craft is to be used. Acknowledgements The author would like to thank Brad Coleman at Broadcast Microwave Services and Adam Doskocil at MP Antennas for their help with researching this article. February/March 2016 | Unmanned Systems Technology An omnidirectional multi-element antenna (Courtesy of MP Antennas) Data transfer links use an antenna to transfer video and other data quickly to a handheld terminal, so the electronics can be sealed against moisture or dust The Boeing X48-B uses three blade antennae, for telecommand, telemetry and video links (Courtesy of NASA)