Unmanned Systems Technology 038 l Skyeton Raybird-3 l Data storage l Sea-Kit X-Class USV l USVs insight l Spectronik PEM fuel cells l Blue White Robotics UVIO l Antennas l AUVSI Xponential Virtual 2021 report

84 Focus | Antennas in the pursuit of what needs to be a highly integrated solution. The software is just as complex: mastering programmable logic to ensure signals are always processed correctly across potentially hundreds of transceivers, digital buses and circuit boards takes much time and effort. Also, the fundamental issues around optimising the waveform for range and direction requires considerable management at both the physical and IP levels, to ensure that the fidelity of data received is not sacrificed for the sake of speed and network size. Managing all this collectively and packaging it into a transportable package can however be achieved with sufficient r&d, with some solutions weighing as little as 2 kg (power supply included). That is a markedly smaller size and weight than the 5G base stations currently being built, although the antennas are rather more complex to develop and optimise. Coaxial cables To ensure the fidelity and security of signals between antennas and radios, high-quality coaxial cables must be used during the integration process. Much like the antennas themselves, different products are available to suit different vehicle requirements. Typically the jackets form the main point of differentiation in terms of the trade-off between weight reduction and ruggedness. Polyethylene harnesses for example make for some of the more lightweight coax cables for UAV applications, and can be combined with polyurethane for fuel resistance if used in an engine-powered system; the latter would never be used in a manned vehicle, owing to toxicity concerns. Also, with some components in defence industry and high-altitude UAVs needing to have very long lifetimes, Teflons and other polymers with good dielectric properties are combined with vapour sealing for greater environmental ruggedness amid changing altitudes, air densities and condensation levels, which could otherwise damage the cables. Different conductive shielding configurations are also installed in coax cables to ‘catch’ EM radiation, preventing leakages of signal data to the outside of the cables, as well as ingress of foreign signals into the cable that could disrupt or corrupt comms fidelity. The most effective shielding option is generally metal foils. These completely encase the cable, and protect against noise and leakages more effectively the thicker they are, but they become inflexible if they’re too thick. Braided metal shielding is less expensive than foils, as less raw material is used, but the gaps in it can make it less effective. Modern designs however increasingly combine a thin foil with a braid as a compromise between flexibility and efficacy. The advent of swarm operations is spurring development of more compact coaxial cable and connector technologies than ever. Small UAVs for swarming could feasibly move beyond even MIMO antenna configurations and integrate significant numbers of micro- antennas (and hence antenna wiring harnesses) in their structures. The diversity of antennas means devoting more weight, internal volume and power to make it easier to hop between frequencies to prevent comms losses, but by using multiple antennas and frequencies, the chances are that at least one will work amid frequency congestion and multi-path effects. Coaxial cables therefore have to mitigate interference with each other more effectively or suffer wear within cramped internal electronics. More flexible designs and materials can be expected to follow in the future. Conclusion In addition to the miniaturisation of antennas and their ancillary components, newer generations of UAVs carrying greater weights and flying at increasing altitudes are expected to spur larger and more powerful antenna structures in the future. Considerable r&d is being conducted around the world to ensure these next- generation antennas can enable this new wave of connectivity in mobile systems safely, in line with however frequency band regulations on comms and GNSS might evolve in the years ahead. Acknowledgements The author would like to thank Giri Baleri and Ed Norse at Trimble, Allen Crawford, Julien Hautcoeur and Gyles Panther at Tallysman, Atle Sægrov at Radionor, Thomas Raggl at PIDSO, David Murray, Kevin Moyher and Carrie Obedzinski at Times Microwave, Chris Jones at Southwest Antennas, and Jeff Butler and Amol Parikh at Doodle Labs for their help with researching this article. June/July 2021 | Unmanned Systems Technology Coaxial cables for UAVs can use lightweight materials that would be unsuitable in manned vehicles owing to their toxicity (Courtesy of Times Microwave)