88 Product focus | Antennas Optimisation of such systems makes judicious use of spectrum analysers and vector network analysers (VNAs) for cycling the handcrafted elements to observe in real-time the frequencies they are being attuned for. Doing so produces metrics that directly inform how the lengths, geometries and orientations must be tuned across its 3D structure to achieve the customer’s desired polarisation, frequency, bandwidth and so on. Despite being handmade, such antennas can be manufactured in volumes of tens of thousands per year, with lead times of less than a few weeks for batches of a few dozen or hundred. Hence, granular details on their production methods are proprietary, and many of the designs are patented, with different ones being optimal for UAVs, UGVs, USVs, stationary GCSs, body-mounted GCSs and so on. The evolving antenna Technological advancements in other areas are helping to optimise antennas to meet the pressing requirements of today’s uncrewed systems. As vehicles integrate higher numbers of data links, the development of antennas with internal bandpass and band-reject filters greatly enhances signal selectivity and minimises interference from colocated radios working at different bands, thus improving comms clarity and integrity for each link. Increasingly popular forms of internally filtered antennas include filtering microstrip antennas, filtering dipole antennas and (for 5G networks in particular) millimetre-wave filtering antennas. Also becoming more popular and widely offered for GNSS use are helical antennas. These have not been historically preferred by geospatial surveyors due to the instability of their phase centres – the apparent point from which EM radiation seems to spherically emanate – which limits their repeatable accuracy to a centimetre rather than millimetre level. However, for uncrewed systems, centimetric accuracy is often more than sufficient, and helical antennas are among the most weight-efficient configurations available, competing with monopoles and patches, but unlike the latter two, helical antennas do not require a ground plane to work, making them easier to integrate and operate. Additionally, as UGVs increasingly work in crowded streets and buildings, and as USVs become permanent fixtures of harbours, oil rigs and wind farms, the chance of accidental collision rises dramatically (while an uncrewed vehicle’s obstacle avoidance may work perfectly, human feet, moving doors and strong waves may not oblige). Fortunately, significant improvements in the mechanical robustness of new antenna products through selecting, adapting and validating enclosure materials and geometries from other ruggedised componentry have been achieved, reducing the rate at which they are damaged in operation or need replacing. Such improvements are also now accounting for chemical corrosion risks, which are pronounced risks for UAVs and UGVs performing agricultural spraying. As well as high vibrations and impact risks, USVs working amid strong sea states or UGVs on uneven terrain can suffer intermittent comms losses (depending on the power, polarisation or other factors of their antenna), but the development of articulated adjustment capabilities now enables antenna angles to be adjusted by up to ±90° to optimise signal reception and transmission by adjusting the antenna’s angle. June/July 2024 | Uncrewed Systems Technology Optimising the antenna element through anechoic chamber tests and other means is vital to achieving the right performance and radiation pattern (Image courtesy of Southwest Antennas)
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