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20 In conversation | Kevin Bean 60,000 ft, as per aircraft traffic regulations. That is where we need to fly to sit above the weather and be able to provide a comms service over a large area, and legally use the HAPS-dedicated parts of the RF spectrum for our 5G activities that we want – typically around 2.1 GHz. “It’s also a good place to fly a comms payload since there’s far less interference in terms of shadowing from mountains, and stratospheric winds are nice and low there. We need to station-hold with high stability if we’re going to provide a high- quality service to telecoms operators, let alone get the aircraft certified.” As the HAP flies, it powers its antenna in order to enable transmit-receive of cellular comms across a 140 km- diameter circular area below. Collectively, a formation of seven such vehicles could provide 5G across an area roughly equivalent to the southern half of England. Airborne 5G antenna At roughly 3 x 3 m, the HAP’s payload system is the largest civilian airborne antenna in the world. It is a digital steerable phased-array antenna weighing 140 kg, composed of 2048 dual polarisation phased-array transceivers with a transmission power output equal to 500 terrestrial antennas. “We’re not a low-Earth orbit satellite [defined as 160 to 2000 km above the surface of the Earth], so we’re not that far away from the ground – the stratosphere sits 12 km above temperate regions and 20 km above the equator – meaning we get latencies of up to 1 ms, which is better than a normal mobile phone’s latency. Whether you’re in logistics, transport or emergency services, if you can genuinely notice discrepancies of 1 ms, you’re superhuman,” Bean muses. An onboard hydrogen power generation system will supply 22 kW of power for running the antenna and onboard telecoms systems. The antenna will dynamically adjust itself to create theoretically any cell pattern on the ground in order to provide targeted coverage to different villages, streets, motorways and communities. “At 60,000 ft, the HAP’s coverage of up to 140 km would provide a great service for rural areas. But say for example you need a 5G boost in an area of high population density; we can adjust the beam pattern or use a different frequency or waveform to shrink our coverage area and provide higher data densities where needed,” Bean says. “We’re also waveform-agnostic; we use a bent pipe architecture, which means we can transmit and receive 3G, 4G, 5G February/March 2022 | Unmanned Systems Technology Bean and his team will engineer each HAP to supply 5G, 4G or 3G internet over a 140 km-wide area – the equivalent of 500 terrestrial antennas (Courtesy of Stratospheric Platforms) TWI and Stratospheric Platforms have worked together for the past few years to study optimal liquid hydrogen storage methods (Courtesy of TWI)