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

38 Cellular Cellular connections are sometimes used for unmanned aircraft, and are an option for ground vehicles as there is good coverage in cities and towns from existing mobile phone networks in many countries. The challenge though comes in rural areas that have no cellular coverage. Bands range from 800/900/1700/1800 MHz for lower-rate GPRS data to 2.6 GHz for 3G and 4G, while next-generation 5G cellular networks are aiming to have a far lower system latency and so are a contender for future driverless car data systems. 5G frequencies were allocated globally by the World Radio Consortium in 2015 (WRC-15) to include longer range 700 MHz links for densely populated urban areas, as well as opening up the 2.1 GHz and 2.6 GHz bands to provide more capacity. The 5G links will benefit from the development of cellular antennae and the availability of high-performance steerable active antennae on mobile phone base stations to provide data rates of up to 10 Gbit/s. The standards for 5G are still being defined but are expected to be formalised by 2018, with networks rolling out in 2020. Another factor in the development of antenna systems is demand for the unlicensed 2.4 GHz band, which is used for wi-fi as well as hobbyist remote- controlled quadcopters and aircraft. It is providing a volume market for antennae, which is driving down costs. V2V bands To provide communications links between vehicles (vehicle-to-vehicle, or V2V) and to roadside infrastructure (vehicle-to- infrastructure, V2I), a range of antennae are using the Dedicated Short Range Communication (DSRC) standard. The frequencies are 5850-5925 MHz in the US, 5855-5925 MHz and 5470-5725 MHz in Europe, and 5770-5850 MHz in Japan, using fin and simple planar antennae to support short-range links between cars and to the roadside infrastructure. The roadside antennae need more sensitive omnidirectional capability and also need to be robust enough to withstand weathering. However, the cost of installing the roadside infrastructure is leading autonomous car makers to look at satellite connectivity. Satellite Satellite networks can provide comms links in a number of bands from craft in a geostationary orbit, and there are several operators providing such global data services. These will be most useful for the planned large unmanned ships, which will not have size and weight restrictions and can therefore be fitted with satellite antennae. Larger unmanned aircraft also have the space to accommodate smaller satellite antennae. For higher data rates, the new generation of satellites are using the Ku-band (12-18 GHz) and the Ka- band (26.5-40 GHz). These offer data rates from 33- 50 Mbit/s via a small mechanically steerable satellite dish- style antenna for larger aircraft, although there are conformal antennae with lower size and weight that are now capable of receiving the signals. Types of antenna There are many different antenna technologies, each with their own trade- offs for the different frequency bands and applications from the craft to the ground station. The simplest antenna, and probably still the most popular, is the dipole type. This is essentially two straight rods or wires that resonate with the signal, capturing a standing wave in the conductor that generates a current captured by connectors at the end. The most common form is the half- wave dipole, where each rod element is about the length of a quarter of the wavelength, so the whole antenna is a half-wavelength long. This is vertically polarised and omnidirectional around the middle of the antenna, and this lends itself well to the 1-5 GHz bands. Microstrip antennae are made from etching an antenna element pattern in a metal trace on an insulating substrate such as a printed circuit board, and uses a continuous metal layer on the reverse as the ground plane. The etched pattern allows these antennae to be created in different shapes, such as square, February/March 2016 | Unmanned Systems Technology The planar satellite antenna for Toyota’s concept car (Courtesy of Kymeta) The unlicensed 2.4 Ghz band, which is used for hobbyist remote- controlled aircraft, is providing a volume market for antennas and reducing costs