Unmanned Systems Technology 033 l SubSeaSail Gen6 USSV l Servo actuators focus l UAVs insight l Farnborough 2020 update l Transforma XDBOT l Strange Development REVolution l Radio telemetry focus

bandwidth links such as video, and the lower bands for other telemetry. The 802.11 standards also extend into the millimetre wave band, particularly above 59 GHz. 802.11ad and its successor, 802.11ay, add support for beamforming and phased array antennas to improve the range of mmwave links in these unlicensed bands. The channels defined in 802.11ad are 1.8 GHz wide, which gives much more flexibility than lower frequency bands. Halving the channel width halves the noise, and gives a 3 dB improvement in the link budget. A quarter-channel gives 6 dB and doubles the range, albeit at lower data rates. If the required data rate is only 100 Mbit/s then that gives the longer range. These standards – 802.11ay is being approved this year – also add beamforming and phased array antennas. This is driving a new generation of active antenna designs that can be integrated alongside the radio in a single module. Different antennas can be used for the 24-29.5 GHz band with 5 Gbit/s data, and the 57-71 GHz with 7 Gbit/s. These provide support for six full RF channels according to the IEEE 802.11 standard, with additional support for half- and quarter-channels. The performance of the antennas is critical to the performance of the links in the mmwave bands. While the wide bands give higher bandwidth links, the antennas have to send and receive over much wider bands than mainstream 5G or wi-fi. While radar system designers have experience of working with such antenna technologies, they have to be miniaturised and reduced in cost for use in ground vehicles and UAVs. That means adopting multi-layer construction techniques optimised for low cost using fibre-resin substrates and standard process technology, and eliminating exotic soft-board or ceramic substrates. A 64-element beam-steering antenna configured in a two-dimensional scanning array with 22 dBi gain across the full frequency range can be 87 Radio telemetry | Focus and weighs only 57 g. It draws 1.16 A at 28 V while providing more than 10 W of OFDM power using binary phase-shift keying coding, or 0.65 A at 28 V with 2 W of OFDM power using 64 quadrature amplitude modulation coding. Millimetre wave The millimetre wave (mmwave) band comes into its own when the data rate is high, for ultra-high definition 4K or even 8K cameras, but it can struggle with range. Mmwave tends to refer to 28 and 38 GHz bands specified for 5G and the unlicensed band from 59 to 72 GHz. Tests in the 28 GHz band have shown that 5G links can run at 2.8 Gbit/s. In the 60 GHz band a radio with 40 dBmi of transmit power can provide 300 Mbit/s. This can be used to provide high data rate links for high-resolution camera feeds or provide telemetry data using much less power than other links. That comes from the higher spectral efficiency of the modulation used. As a result, this is being explored for high-altitude pseudo-satellites (HAPS), which fly at up to 70,000 ft (23 km) to provide broadband services or surveillance. Fleets of HAPS aircraft have also been proposed, and these would need to communicate at that altitude. The difference in operation is important, as at around 60 GHz the radio signals can be significantly reduced by absorption by water droplets and oxygen for a link to the ground. That means links at high altitude can be inherently longer range, although ground stations can have much larger, more powerful beamforming receivers to provide high- bandwidth links. The WARC-19 2019 global radio frequency conference authorised a band at 38 GHz for HAPS, so it is now feasible to broadcast 1-2 Gbit/s to a UAV at 66,000 ft (20 km) altitude using beamforming with the right link budget – that is, with enough power. This would be 10 W of broadcast power, or 10 mW of power consumption for the radio. However, the whole radio system uses around 35 W for the radio, modem and network processor packetisation. It is the network processor that takes most of the power. As of the end of 2019, 3GPP also specifies 28 and 38 GHz for 5G links. With flexible processing, this would allow the mmwave bands to be used for high- Unmanned Systems Technology | August/September 2020 A millimetre-wave evaluation kit (Courtesy of Blu Wireless Technology) Millimetre-wave systems need a complex RF design (Courtesy of Peraso Technology)