Military Technology 06/2021

grams. Both genres of platform are a good deal smaller that conventional medium and large UAVs. This means they have a much smaller radar cross section (RCS) than their larger counterparts. The relatively small RCS of a micro- or mini-UAV may cause a radar to struggle to detect them. There are multiple reasons why a small UAV might be difficult to de- tect using radar, discussing which deserves an article in its own right for a proper examination. Nonetheless, put simply, a small UAV may reflect very little RF energy back to a radar. Radars transmit radio waves, which travel at the speed of light, hit an object such as an aircraft and are reflected back to the radar. By halving the time taken for the radar to transmit the RF pulse and for said pulse to hit the object and return to the radar, said radar can calculate the target’s range. For example, if the pulse’s round trip takes 0.08 milliseconds, it will have travelled 26km and the range to the target is therefore 13 kilo- metres. The problem for a radar is that the pulse’s strength diminishes as it travels from the point of transmission and bounces off a target. The radar must listen carefully to ‘hear’ the pulse reflected from a target. This is complicated by the fact that the ether is a noisy place. Naturally occur- ring electromagnetic radiation, and interference from other radio trans- missions may be received. A target like a small UAV might only reflect a small number of pulses back to the radar, which may be so weak that the radar struggles to ‘hear’ them above the prevailing electromagnetic noise. Thus, the small UAV becomes difficult to detect. Equally, a radar might mistake a small UAV for another target that it subsequently ignores. For instance the radar’s processor detects a few weak pulses from a small UAV, but its software erroneously determines that this is a bird. As a re- sult, the radar may dismiss this target as ‘clutter’ that it does not need to bother the operator with. Other factors further complicate things. Many small UAVs are con- structed from materials intended to save weight. For example, Yuneec’s TYPHOON H PRO hobby UAV is made primarily of carbon fibre. This helps lighten the aircraft and improves its performance. However, materials like carbon fibre can be difficult to detect by radar, compared to the tradition- al metallic surfaces used by conventional aircraft. It is no coincidence that materials like carbon fibre are used in combat aircraft such as the F-22A RAPTOR. Such aircraft are a ‘first day of war weapon,’ designed to The Problem Azerbaijan’s victory clearly demonstrated the effectiveness of UAVs on the battlefield. They proved their worth, not only as intelligence, surveil- lance and reconnaissance (ISR)assets, but also for kinetic effects. The use of UAVs in future wars is unlikely to diminish. The global UAV market is growing. In September, Precedence Research stated that demand for UAVs could rise to $36 billion ( € 32 billion) by 2030, valuing the market at some $14.3 billion in 2020. The research house predicted that, on aver- age, the market will increase by 14% annually between 2021 and 2030. Should these predictions materialise, by 2030 there will be many more civilian and military UAVs than there are today. This increase in the global fleet size will see more UAV use on the battlefield, and will have an impact on the civilian world as well. Incidences of unauthorised civilian UAV use are growing – this writer’s apartment building was ‘buzzed’ by a UAV several months ago. Local police re- vealed that they had no way of detecting or intercepting the UAV. In the wrong hands, a UAV can cause disruption or worse. On 8 January 2019, flights at London’s Heathrow Airport were suspended for an hour follow- ing a UAV sighting. Famously, between 19-21 December 2018, flights at London’s Gatwick Airport were seriously disrupted after similar reports. The disruption cost the airport and airlines in excess of $69 million, ac- cording to British media reports. Unauthorised drone flights may exercise impact over and above the financial, however: on the night of 8-9 August this year, in Nimes, southern France, a UAV supplied contraband, includ- ing weapons, to prison inmates. UAVs can be detected with conventional optronics or infrared sensors. Nonetheless, weather can impinge upon optronics’ ability to accurately detect and track UAVs. Radar is another useful technology, although de- tecting and tracking a UAV with a ground-based air surveillance radar is easier said than done. Large MALE-like UAVs are comparatively easy to detect and track with a radar. These aircraft are typically large, mimicking the size of light aircraft. They also fly in a manner reminiscent of a conven- tional aircraft. Things become interesting as UAVs get smaller. The Physics Mini- and micro-UAVs are particularly challenging: mini-UAVs typically weigh between 1-25kg, whereas micro-UAVs can weigh as little as 250 Specialising in radar, communications, electronic warfare and all things C4I, Thomas Withington is a defence journalist, writer and regular contributor to MilTech . Thales’ GAMEKEEPER radar was developed by Aveillant. It has been deployed at several locations to help protect against UAVs entering runway glide paths. (Photo: Thales) C4ISR Forum MT 6/2021 · 61