Unmanned Systems Technology 019 | Navya Autonom Cab | Batteries | UGVs Insight | UAV Factory UAV28-EFI | Swiss Aerobotics Hummel | UMEX 2018 report | Antennas | Oceanology International 2018 report

81 and also focus waves onto the aerial for reception. Beyond this, however, there is a wide range of antenna types to choose from, with varying combinations of RF performance, frequency, size, weight, power, aerodynamic signature, polarisation and construction qualities. Given that the number of antenna types available is greater than what is optimal for the intended application of the vehicle, the ideal antenna for an unmanned system’s intended mission and environment depends on a range of factors. For an aerial vehicle, it may include the speed at which it will fly, the distance it is required to travel from the ground control station (GCS), the type of terrain it will travel over, the material used in the construction of the hull, and where on the vehicle the designer has left space for it to be integrated. Some of these will apply to a UGV as well, but there will be other questions regarding the degree of multi-path interference it might face, and whether it will be operating in urban environments, under forest canopies or anywhere with a lot of reflective or suppressive obstacles. While autopilots and sensor algorithms allow fully autonomous operation beyond visual line of sight (BVLOS), until such missions are permitted by the pertinent regulations a constant link between the vehicle and its control station must be maintained. Furthermore, higher-stakes applications requiring real-time HD video feeds and controller responses require an antenna set-up with a high bandwidth and robust link. As unmanned vehicle data links widen from the UHF and L bands to the Ku band and beyond, achieving the ‘optimal’ antenna set-up becomes an exponentially complex project. It therefore becomes evermore crucial for vehicle manufacturers to pay close attention to the defining parameters and latest advances in antenna systems to avoid potentially catastrophic losses of comms or costly gaps in data capture. Polarisation Antennas will exhibit different orientations of their radiated EM waves, and this polarisation can be linear, acting along a particular plane in the direction of propagation, or circularly polarised, in which the radiation’s field rotates in time perpendicularly to its direction. As unmanned systems traverse their mission spaces in the air, on the ground or the water’s surface, an antenna’s polarisation is at risk of changing in tandem with a vehicle’s orientation. This polarisation mismatch is especially pronounced with single-input single- output radios, where only a single antenna is used in both the transmitter and receiver modules. Such systems can experience losses of up to 80 dB of signal, owing to movements of the vehicle and changes in atmospheric conditions. The popularity of multiple-input multiple-output (MIMO) radios, which use multiple antennas, has grown significantly in recent years, not least because different antennas can have different polarisations. This could enable a MIMO-enabled GCS using linear polarisation to exploit horizontal as well as vertical polarisations. A UAV with a vertically polarised antenna installed could therefore maintain a favourable signal-to-noise ratio (SNR), even while banking from side to side and changing its polarisation to horizontal, since MIMO antennas can receive separate and uncorrelated signals as they take advantage of the multi-path propagation characteristics. Alternatively, a circular polarisation may be preferable to vertical linear set-ups for unmanned aerial systems as they are less affected by clouds or precipitation. The nature of circular polarisation also means the vehicle is always properly aligned with its GCS as far as antenna polarisation is concerned, regardless of pitch, roll or yaw. That can help prevent gain issues or signal fading that might otherwise reduce the effective range of the craft’s comms system. UUV and USV designers can also be selective about the polarisation of their antennas, depending on the sea state in which a given system is meant to operate. The more severe the rolling and movement expected from waves, the more specific the antenna requirements. Subsea craft are likely to suffer far worse from this, despite only using RF comms when surfaced. Being far less protected against waves than USV antennas are, they may need telescopic mechanisms to raise their antennas above the Antenna systems | Focus Unmanned Systems Technology | April/May 2018 By integrating multi-antenna set-ups, MIMO radios can exploit both vertical and horizontal polarisations, avoiding the intermittent signal disruptions that can occur with single-input, single-output radios (Courtesy of Persistent Systems)