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

34 A lthough the antenna is one of the last items to be specified in an unmanned system’s design, it ends up being one of the most critical. Antenna systems are essential for communicating with craft, sending back data from them and for acquiring their position, as well as for navigation systems and transponders. The requirements of a wireless control link determine the design of an antenna, which in turn can have a significant impact on the performance of a craft. One way to achieve an acceptable link is to have multiple antennae across the body of a craft. However, this requires more holes in the airframe, which increases the drag on a UAV and reduces its range and time in the air. Using conformal antennae that mould to the shape of the craft can reduce this drag, but they are suitable only at certain frequencies. Using circularly polarised antennae can provide a more reliable link, but they are larger and heavier than the simpler, vertically polarised dipole antennae. Other options include scanning directional passive antennae, which can use a gimbal to direct a signal back to a ground station to provide more range, but they too are heavier to implement. Active scanning antennae are also heavier and can struggle with changes in the polarisation of a link. The choice of frequencies also determines the size and weight of the antenna and the data rates that are possible, as well as the size of the ground plane that is needed to make an antenna work effectively. All of this leads to innovative antenna design across a range of applications and frequency bands. Antenna design is also a key element in the sensor systems in unmanned craft, particularly for satellite navigation. The various global navigation satellite systems (GNSS) – GPS from the US, Russia’s GLONASS, the EU’s Galileo and China’s BeiDou – have slightly different frequency requirements that need to be considered in the antenna design if all frequency bands are to be supported. The effectiveness and reliability of the reception of the satellite positioning signals is vital for accurate navigation. Nick Flaherty investigates the growing range of technologies and design options for this key element of unmanned systems Are you receiving me? February/March 2016 | Unmanned Systems Technology The height of a ground station’s antenna has a dramatic effect on a UAV’s range (Courtesy of BMS)