85 with electromagnetic fields to receive or transmit RF signals. It typically presents as a metal rod as per a monopole antenna (in ‘whip antenna’ form; monopoles housed in a blade-like aerodynamic fairing are referred to as blade antennas) or two symmetrical rods per one dipole antenna, a flat square of metal in a patch antenna, or as many elements combined in an array antenna. As the active element directly regulates the antenna’s resonant frequency and radiation pattern, optimising it is fundamental. Beyond the element is an internal network of devices typically comprising capacitors, inductors and transformers designed to optimise the impedance matching with the coaxial cable that links the antenna with the radio, thereby achieving the highest possible rate of power transfer and the lowest possible rate of radio signals being reflected back from the antenna (which leads to losses and distortions). Following this, bandpass or band-reject filters are application-critical circuits that allow signals of certain frequencies to pass through the antenna and block others from undesired radio frequency (RF) bands, so choosing the right filters is paramount for safeguarding signal integrity against congestion, interference, and so on. Internal matching networks and filters tend to be most complex in ultrawideband (UWB) antennas; GNSS and satellite communication antennas will often also integrate a low-noise amplifier (LNA) somewhere between the internal matching network and receiver to boost the very low-power signals coming from satellites without excessively decreasing signal-to-noise. Like filters, LNAs must be tuned to accept and amplify signals, particularly frequency bands, and, by comparison, drown out-of-band signals. As one nears the radio or GNSS receiver, one may find a spring base for allowing the antenna to bend and sway flexibly without breaking, maintaining its integrity and functionality in hazardous environments prone to physical contact, such as forests, warehouses or cramped urban corridors. If using a monopole antenna, one will find a counterpoise for reflecting the active element’s electromagnetic (EM) waves into an efficient radiating system with the ideal radiation pattern and impedance characteristics (naturally, size and positioning closely relate to antenna performance). At the base, one finds a connector – usually a SMA, N-Type or BNC, chosen for the frequency range and power levels of the application – and a coaxial cable, which together link the antenna to the radio or receiver. Signal integrity and connection efficiency depend on the quality of the connector and cable. While these might not seem like an especially long list of building blocks, they encompass a massive algorithm of instructions that antenna manufacturers require of uncrewed systems engineers at an early stage to do their job optimally. Conversations with antenna makers A detailed description of the intended mission of an uncrewed vehicle will define the range, data rates, GNSS accuracy, and likelihood of obstacles or interference sources, which the antenna must be designed around (and extensive discussion of these points between customers and suppliers should account for how these may change between stages of an operation). A new UAV’s design bears numerous factors of high concern to antenna manufacturers who want to achieve the ideal construction, placement and specifications for the antenna they end up supplying, in order to maximise project success, and minimise failures and complaints down the line. For instance, the presence, type and geometry of carbon fibre used in the hull can act as a ground plane, altering the antenna’s radiation pattern, or it can block RF signals outright, meriting the use of RF-transparent materials over select parts of the body. Similarly, RF-isolating the antenna will become more important as the potential for selfjamming from other onboard electric or electronic subsystems rises. Additionally, the integrator’s request for a certain range and strength of data links for a mission’s duration may exceed what the available onboard power can provide due to insufficient battery or fuel capacity, or sharing power with other onboard systems (which may include power-hungry payloads such as Lidar, 4K cameras or mid-wave infrared (MWIR)). A UAV with a large, hybrid powertrain could be well placed for powering strong and consistent links for control, video and satellite navigation. However, if that powertrain is there for the aircraft Antennas | Product focus Uncrewed Systems Technology | June/July 2024 The use of flexible antenna bases is increasingly valued for preventing impact damage as uncrewed vehicles squeeze through cluttered areas (Image courtesy of Southwest Antennas)
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