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57 Griff 135 | Digest Small-object detection James Henderson, millimetre-wave engineering lead at Plextek DTS, says the radar system is based on Passive Electronically Scanned Array technology and that it operates in a band of frequencies in the licence-exempt 60 GHz waveband (a band the company has also investigated for UAV non-line-of- sight comms in urban environments). This equates to a free-space wavelength of around 5 mm, and operating in the millimetre-wave (mmW) band enables a small radar to achieve high resolution, detecting small objects at extended range. Radars operating at 60 GHz are also largely unaffected by adverse weather conditions such as rain, fog and dust within their intended operating range. The 60 GHz band does, however, have a minor linear loss associated with atmospheric oxygen absorption. This causes only a small reduction in the received signal level over the radar’s operating range, but over longer distances it significantly reduces the radar’s probability of intercept in military applications and lowers the risk of interference with other RF systems in civilian use. While the demonstrator operates on about 30 W, future flight tests will use Clarus, which will draw less than 10 W, measures just 200 x 100 x 80 mm and weighs less than 500 g. To achieve this power reduction Plextek DTS developed a radar processor architecture centred on a Xilinx Zynq SoM FPGA. The core transceiver technology is a mmW antenna integrated into a radio- frequency printed circuit board, which also contains the mmW electronics. Henderson explains that although there were many technical challenges associated with this approach, it makes the design inherently small, lightweight and efficient for the mmW signal. Plextek DTS’ business development director Peter Doig says ground tests with the radar mounted on a van have demonstrated the miniaturised radar’s ability to detect a wide variety of relevant objects and infrastructure, including roadside foliage and infrastructure such as central reservation barriers, out to ranges of 300 m. It can detect returns from trees and penetrate their leaf canopies, enabling it to detect the terrain and obstacles under the trees, and has demonstrated this capability at up to 100 m. One capability that Forde expects to be particularly important as standards and regulations governing UAV operations develop is sense & avoid, to protect against air-to-air collisions. A small mmW radar may not have sufficient range, so that capability is more likely to be an integrated comms and ranging system used in conjunction with a miniaturised, lower frequency microwave radar, which Plextek DTS is also investigating. Besides the large UAVs on which it is currently focused, Forde says customers are asking for vehicles with payloads of around 5-10 kg that can be certified for flight in populated areas under future regulations. The company plans to begin developing these this year, demonstrating one in cooperation with Airbus over Oxfordshire in the UK under the EU’s Harmony sustainable transport programme. Unmanned Systems Technology | February/March 2020 Dimensions (ready to fly): 226 x 241 x 47 cm Folded dimensions: 77 x 144 x 47 cm Maximum payload: 50 kg Maximum take-off weight: 125 kg Endurance with 30 kg payload: 20-25 minutes Some key suppliers Propellers: Mejzlik Flight controller: MicroPilot Navigation radar: Plextek Battery cells: Sony Murata Navigation system: Near Earth Autonomy Motors: Rotex Electric Comms links: Microhard Specifications Plextek’s e-scan radar technology demonstrator has been flown on this off-the-shelf DJI S-1000 octocoper (Courtesy of Plextek)