在乌克兰与俄罗斯之间这场大卫对歌利亚式的战争中，无人机被证明是一种极大的均衡器。乌克兰的短程飞行器正在切断俄罗斯向其占领部队的补给线，而远程版本则袭击远至西伯利亚的炼油厂、机场和仓库。
In the David and Goliath war between Ukraine and Russia, drones have proved a great equaliser. Ukraine’s short-range aircraft are cutting Russia’s supply lines to its occupying troops, while long-range versions attack oil refineries, airfields and warehouses as far afield as Siberia.
然而，并非所有军用无人机都携带弹头。许多反而被用于侦察和定位目标。其中大量无人机以光学或红外频率收集数据。但有些属于信号情报（SIGINT）领域的无人机则监听无线电波。在这一类别中，还有一些无人机的目的并非理解被广播的内容，而仅仅是识别并定位它，以便更好地攻击它——这一领域被称为ESM，即电子支援措施。
Not all military drones, however, carry warheads. Many are used instead for spying and target location. A lot of these gather their data at optical or infrared frequencies. But some, involved in the field of signals intelligence, or SIGINT, listen out for radio waves. And within that category are those which seek not to understand what is being broadcast, but merely to identify and locate it, the better to attack it—a field of endeavour that goes by the name of ESM, or electronic support measures.
据智库皇家联合军种研究所的电子战专家托马斯·威辛顿称，其结果是一场军备竞赛，用于控制无人机的无线电频率不断向频谱的高端和低端迁移，以试图逃避探测。跳频电台每秒从一个波长跳到另一个波长数千次，而且速度越来越快，因此发射机可能只是短暂可见；信号越来越多地被伪装以融入背景噪声。
According to Thomas Withington, an electronic-warfare expert at the Royal United Services Institute, a think-tank, the result has been an arms race in which the radio frequencies used to control drones have migrated ever further up and down the spectrum, in attempts to evade detection. Frequency-hopping radios, which skip from one wavelength to another thousands of times a second, are getting faster, so a transmitter may be visible only momentarily; signals are increasingly disguised to merge into background noise.
威辛顿博士指出无人机为ESM带来的优势。一套安装在卡车上的系统配有十米天线，可以探测到大约13公里外的发射机。同样的接收机装在海拔1000米的无人机上，则可以看到130公里外。当天线装在无人机上时，在攻击可能来自任何方向的情况下也更有用。它避免了地形造成的盲区。
Dr Withington notes the advantages drones bring to ESM. A lorry-mounted system with a ten-metre antenna can detect transmitters roughly 13km away. The same receiver on a drone at an altitude of 1,000 metres can see for 130km. Having antennae on drones is also more useful when an attack may come from any direction. It avoids blind spots caused by topography.
乌克兰人不愿谈论他们正在做什么。但并非所有研究都在内部进行。在6月举行的欧洲防务展上，德国制造商阿罗尼亚推出了一套可安装在无人机上的信号情报电子设备。开发人员称，三架搭载该设备的无人机协同工作，可在最远75公里外将发射机定位到25米以内。
The Ukrainians are reluctant to discuss what they are up to. But not all their research is being done in-house. At Eurosatory, a European defence exhibition held in June, Aaronia, a German manufacturer, unveiled a SIGINT electronics package that can be mounted on a drone. The developers say three such drones working in tandem can pinpoint transmitters to within 25 metres from up to 75km away.
阿罗尼亚的产品重5公斤，携带起来颇为不便。总部位于特拉华州的Sky Spy公司最近展示了“001号特工”，这是一个重500克的电子设备，可安装在小型Orqa四旋翼无人机上。在爱沙尼亚的一次演习中，该设备被证明能够探测、识别和定位“敌方”无线电。001号特工还具备机载处理能力，并与无人机摄像头相连，因此它可以朝发射机移动并拍摄视频，供操作员确认信号来源的身份。
At 5kg, Aaronia’s product is inconveniently heavy. Sky Spy, based in Delaware, recently demonstrated Agent 001, a 500-gram electronics package that can be mounted on a small Orqa quadcopter. This proved able to detect, identify and locate “hostile” radios as part of an exercise in Estonia. Agent 001 also has on-board processing, linked to the drone’s camera, so it can move towards a transmitter and capture video for its operator to confirm the identity of the source.
威辛顿博士表示，小型无人机的一个局限是它们所能承载的处理能力有限。而这种处理能力对于筛选信号数据至关重要。例如，无人机的控制信号可能隐藏在Wi-Fi信号中。
One limitation of small drones, says Dr Withington, is that the amount of processing capacity they can carry is restricted. Such capacity is essential for sifting through signal data. Drone-control signals may, for example, be hidden in Wi-Fi.
然而，新型处理器和人工智能软件正使小型无人机的能力大幅提升。北卡罗来纳州NxGenComm公司开发了一款名为“仓鸮”的设备，可安装在无人机上。NxGenComm的市场总监戴维·格罗斯表示，“仓鸮”会跟踪Wi-Fi范围内的所有通信流量，通过分析变化来识别隐藏的军用信号特征。他声称，这一过程的速度足以跟上最灵敏的跳频电台，其能力也足以扫描和分析带宽达800MHz的无线电信号。
New processors and AI software are, however, making small drones vastly more capable. One bit of kit that can be mounted onto a drone, known as Barn Owl, has been developed by NxGenComm of North Carolina. David Gross, NxGenComm’s marketing director, says Barn Owl follows all traffic in the Wi-Fi range, analysing changes to pick out the signatures of concealed military signals. He claims the process is fast enough to keep up with the most nimble frequency-hopping radios, and powerful enough to scan and analyse an 800MHz-wide swathe of radio signals.
情报既可传递给指挥官，也可直接传递给其他单位。在一套拟议的配置中，一组“仓鸮”将与拦截无人机直接联网。当它们探测到来袭无人机时，会发射一架拦截机并将其引导至目标位置，直到操作员能够通过视觉确认目标为止。NxGenComm希望在未来几个月内将“仓鸮”部署到乌克兰，并正在与美国军方客户进行洽谈。
Intelligence can go to commanders, or directly to other units. In one proposed set-up, a parliament of Barn Owls would be linked directly to interceptor drones. When they detected an incoming drone, they would launch an interceptor and guide it to the target’s location until it was close enough for visual confirmation by the operator. NxGenComm hopes to deploy Barn Owl to Ukraine in the next few months, and is in discussion with American military customers.
除了定位敌方无人机，电子支援措施还能帮助识别其控制频率，以便实施干扰。双方都通过让部分无人机经由光纤控制电缆飞行来应对这一威胁，电缆随飞行逐渐展开。这类无人机可携带50公里长的光纤，不发射任何无线电信号。同样，一些具备人工智能的无人机也能在无通联状态下运作，无需操作员输入即可飞行并打击目标。
As well as locating enemy drones, ESM can also help identify their control frequencies so that they can be jammed. Both sides get round this by flying some drones via fibre-optic control cables, which unspool as they fly. Such drones, which can carry 50km of fibre, emit no radio signals. Similarly, some AI-enabled drones can operate incommunicado, flying and striking targets without operator input.
然而，目前绝大多数无人机仍依赖无线电，电子战军备竞赛仍在持续。落后于人可能酿成灾难：如果敌方能干扰通信并击落无人机，自身却保持隐形，必将导致惨重损失。■
In the meantime, however, the vast majority of drones still rely on radio, and the electronic-warfare arms race continues. Falling behind can be disastrous: if an enemy can jam communications and knock drones out of the sky while remaining invisible, heavy losses are sure to result. ■