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

87 Antenna systems | Focus feeding both the left-hand and right-hand signals into the receiver, resulting in reception that is inadequate for the needs of modern unmanned systems. A dual-pin antenna, however, can have one antenna oriented in one axis and another at 90 º to it, the two being effectively deaf to each other. One will have a response to everything in a vertical polarisation, while the other will pick up on the horizontally polarised signals. After a 90 º phase shift, the antenna will have arithmetic equivalency to a circular response. In this way, a dual-pin antenna might be tuned to 1590 MHz and pass a far cleaner circular signal to the receiver. Any resonance from an LHCP signal ought to measure around 30 dB less than that of the RHCP signal. In addition to advances in multi- constellation reception and pre-filtering, improvements continue to be made in size and weight. For UAV designers aiming to achieve longer, more efficient flights, or autonomous road vehicles looking to minimise energy requirements, incorporating dual-feed RTK GNSS positioning with minimal phase centre variation cannot add too much weight or take up too much space in the vehicle. Miniaturisation has been particularly challenging for antenna developers, as demands for high bandwidth typically mean using a larger ceramic head atop the RF assembly, and the heads can suffer from micro-fractures and become unstable as they are made larger. As a result, the dielectric loading (the loading of electrical insulation that enables polarisation) can vary between units. Fortunately, some alternatives to this problem have appeared in the past few years. Some antenna systems now use air as their dielectric core, saving weight. Another option is for dual-feed patch antennas to use capacitive coupling to electronically couple to other circuit elements, and combine signals from different satellite networks with much smaller and cheaper components than previously possible. Additive manufacturing Producing complex RF set-ups for specific applications and environments can entail individually fabricating dozens of intricate elements before mounting and fastening them together. Using CNC machines to make large numbers of antennas for consumer goods does not pose an issue, but they are not cost-effective for manufacturing small numbers of systems, as would be needed for testing prototype vehicles or designing for niche operations, owing to the time and cost involved in retooling and reconfiguring such machines. Additive manufacturing (AM) typically sinters or extrudes only the metal additives that are required to achieve the desired electrical and mechanical performance in the end-product, and needs only software adjustments for customised antenna structures, avoiding costly retooling expenses. This also allows the finished structures to be lighter, and can also avoid the high volume of waste that occurs in conventional antenna manufacturing. The precision of AM-produced parts is also such that conformal antenna assemblies can be designed to fit precisely with the desired aerodynamics of a UAV. Components can be designed and ‘printed’ to act as mounting structures for other systems as well, potentially allowing unmanned systems in the air or elsewhere to carry more hardware than previously feasible. Integrating RF simulators with AM design software, and advances in computing power, have been key to making AM for antennas in unmanned vehicle applications possible. Component designs can now be scaled and reconfigured across multiple simulations in parallel, to resolve specific data link requirements. It also allows design cycles for complicated antenna assemblies to be shortened by months. Modern AM methods work with materials common to RF components, including a range of aluminium alloys with similar weight, conductivity and shock and vibration resistance to 6061 aluminium. Steel, titanium, cobalt-chrome and Unmanned Systems Technology | April/May 2018 Metal additive manufacturing enables complex antenna structures such as 4 x 4 element arrays to be fabricated along with other components as a single integrated part (Courtesy of Optisys)