87 seeking transponders configured for ADS-B (as well as remote ID, but only where US and European law requires it). Also critical are the efforts of transponder manufacturers in developing transponders with thoroughly minimised weight, size, power consumption and failure modes to fit within the greater need for efficiency and autonomy in uncrewed system airworthiness. Innovations and investments in the UAV space are enabling the bulk production of transponders (including Mode S and S-ES compliant systems) smaller than smartphones that can broadcast scores of kilometres away with ten or fewer watts of power, as well as larger but no less power-efficient systems for broadcasting farther away in applications requiring hundreds of kilometres of traceability. As well as devising architectures and leveraging new components for advancing SWaP optimisation, new transponder standards are emerging that will soon be key for certifying which units and companies meet the highest grades for safety-rated avionics. These certifications are regulated and granted by the FAA, EASA and other aviation authorities, including defence departments defining military certification standards for Mode IFF (interrogation, friend or foe) devices. As of writing, DO-181F and the Technical Standard Order (TSO) C112e are the latest to define required performance standards on transponders, while DO-260C and TSO C166b govern ADS-B minimum performance and certification requirements. On top of these, future airborne collision avoidance system (ACAS) regulations for mixed crewed/uncrewed airspaces now have FAA-defined groups of algorithms, created through work with MIT and Johns Hopkins University, and categorised based on the size, weight and configuration of UAV (particularly whether they are above or below 25 kg, crewed or uncrewed, and fixed-wing or rotorcraft design). These will fuse ADS-B transponder data (labelling this ‘cooperative’ data) and radar or camera data (‘noncooperative’) into response formats that are stable and predictable as regulators like them, because simply installing cameras into every vehicle and trusting them to duck below or dodge other vehicles would be a haphazard and unsafe way of organising the world’s airspaces. All of this is driving the design evolution across transponders, being formed through discussions between regulators and leading manufacturers, so that integrating such products can help reduce the barriers to routine flying for high-end UAVs. Anatomies and ecosystems The components of a transponder-type device can be few or many, depending on the kind being considered. If one thinks principally of an ADS-B Out solution, whether of higher or lower power, then one will find, at a minimum, a highly sensitive receiver for detecting low-power ADS-B signals from tens or hundreds of kilometres away, and a high-power transmitter for delivering such signals over such distances on defined frequencies. Just as important is an integrated circuit for deciphering received signals, and requesting the necessary onboard data for generating and communicating a signal of its own. As transponders are required by standards to respond Transponders | Product focus Uncrewed Systems Technology | August/September 2024 Compliance with TSOs is critical for certification. In future, algorithms for ACAS will enable and signify higher levels of airspace safety (Image courtesy of Sagetech)
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