Issue 37 Unmanned Systems Technology April/May 2021 Einride next-gen Pod l Battery technology l Dive Technologies AUV-Kit l UGVs insight l Vanguard EFI/ETC vee twins l Icarus Swarms l Transponders l Sonobot 5 l IDEX 2021 report

80 transmitted, based on inputs for requested data such as GNSS, altitude or velocity. These chips come in several varieties, with differing component architectures, most of which are increasingly SWaP-optimised for UAV integration. Most emerging transponder chip varieties are engineered for ADS-B comms, but a growing number are designed according to the FLARM protocol, given how it goes beyond ADS-B in several important ways. While many organisations strongly recommend FLARM in lieu of ADS-B Out (or other outright replacements of older standards with newer ones), some transponder chips can now embed both functionalities, as well as additional capabilities such as ADS-B In or Modes A and C, into single-chip devices. That is achieved by combining the latest single- and multi-core processors with FPGAs. The latest single-core processors enable all the real-time data throughput and different algorithmic functions needed for ACASs among UAVs in shared airspace, across the most popular protocols being put forward, while weighing 1.5 g or less, allowing form factors suitable even for very small airframes. Multi-core processors also further widen the envelope for handling data and algorithms. This ensures that ground stations and infrastructure have a fallback for coordinating different aircrafts’ transponder signals and flight paths, even if many different modes and protocols are being used within a given patch of sky. In both cases, the capacity of FPGAs for performing a single algorithmic function at super-high rates makes them ideal for ‘outsourcing’ certain core transponder functions from the processor, enabling the processing power to be right-sized for overall SWaP- optimisation of transponder chips. Fusing these components and algorithms is challenging, but the end result enables easier integration and significant future- proofing for how TCAS and ACAS modes might evolve. Board engineering and testing While making SWaP-optimised components is always important for UAVs, the proliferation of smartphones and other IT and telecoms products over the past decade has greatly increased the availability of very small RF and processor units. Also, concerns over the security of supply chains has driven some high-end UAS transponder manufacturers to develop their own RF components either in-house or to work with local partners to develop their manufacturing capabilities. The challenge historically associated with sourcing small, lightweight and high- quality transponder components has therefore been eclipsed by the difficulty of designing them with effective heat dissipation, as well as accounting for their mounting and cabling needs. Various design tools are available from the likes of Matlab, Solidworks and Eagle for optimising the designs of transponder boards for electrical, thermal and radio sensitivity. Finite element analysis through such software is ideal for optimising how the transponder’s PCB and housing dissipate heat, for example. This can also be handled more easily if the housing’s form factor does not restrict engineers’ ability to install their transponders where cooling is available. That means the number and placement of connectors must be minimised, as well as the housing’s size and shape. Excess wiring harnesses consume scarce weight and volume, so to reduce wire counts transponder manufacturers are using fewer connectors and more pins. A single 51-pin rectangular connector can provide all the transponder’s power and data needs (except for the coaxial cables running to the antennas) while enabling a flat, tight shape for the housing. Securing connectors using fasteners or locking mechanisms is also critical for ensuring antennas and autopilots are never accidentally disconnected from the transponder during flight, which would effectively turn a certified aircraft into an illegal one. Of course, different customers have differently shaped pockets of space inside their avionics bays, and may connect their transponders to very different sets of electronics – autopilots and GNSS processors, for example – via serial, Ethernet or other ports. Transponder makers will therefore also often customise their connectors and housings to requested specifications or provide open systems for customers to install their own connectors and cable harnesses. Working with autopilot manufacturers can also ensure common interfacing methods for plug-and-play compatibility between such systems, making life much easier for systems integrators. Beyond integrating transponders inside UAV fuselages, key component choices can help immensely with operating UAVs in shared airspaces. As mentioned, dynamic RF front ends can enable toggling of transmission power to reduce spectrum congestion. They are designed using new forms of power architecture, with high-quality April/May 2021 | Unmanned Systems Technology The ZPX-B Mode 5 IFF transponder from uAvionix is the latest system to have received the DoD AIMS Mk XIIB certification (Courtesy of uAvionix)