Published in the February/March 2021 Issue – Radars on the battlefield track and detect a diverse collection of targets. Is it feasible or desirable to develop a single radar to perform these disparate missions?
Battlefield radars perform four core functions: They can detect people or vehicles, aircraft; Rocket Artillery and Mortar (RAM) fire and even equip vehicles to detect incoming ordnance. Armies must often deploy several types of radar to support the manoeuvre force. This could include Ground Surveillance Radars (GSRs) to detect people, vehicles and some low-flying aircraft such as Uninhabited Aerial Vehicles (UAVs). These maybe reinforced with ground-based air surveillance radars to detect hostile fixed- and rotary-wing aircraft, and UAVs at range, together with Weapons Locating Radars (WLRs) to detect incoming RAM fire. Finally, armoured vehicles may use radars to detect incoming munitions to alert their Active Vehicle Self Protection Systems (AVSPSs). Why have radar engineers not developed a standard, deployable radar that could perform most, if not all, these missions? Would this not save on the cost and logistics having to deploy multiple radars for this array of targets?
A written statement from RADA Electronic Industries notes that these diverse surveillance and detection missions “have very different operational constraints.” This is because they involve “different target types” notes a written statement from Weibel Scientific. The targets each radar type detects all behave in a particular way: “With that in mind, it may be very difficult to solve all these missions at the same time with the same radar.” Nonetheless, a written statement from Blighter cites “a clear move towards the use of multi-mission radars,” although cautions that “trying to achieve a one-size-fits-all” approach inevitably involves compromises.
For example, RADA says that GSRs do not prioritise elevation coverage, unlike ground-based air surveillance radars which must determine an aerial target’s altitude. Furthermore, “ground targets have a very small radar signature,” observes Weibel. “The targets move extremely slowly with a limited line of sight, meaning it is difficult to acquire and track targets which have a tendency to disappear in ground clutter.”
As a result, GSRs need high Doppler resolution. Radars exploit the Doppler Effect. Named after Austrian physicist Christian Doppler, this is the phenomenon by which the frequency of the pulse of electromagnetic energy transmitted by the radar increases when it hits a target moving towards it. Likewise, the frequency will decrease if the object is moving away from the radar. An oft-quoted example of this is the apparent rise in tone of a police car siren as it approaches a stationary observer and its apparent decrease as the police car drives away. This is because the crest of each wave of radio frequency (RF) energy transmitted by the radar takes less time to reach the antenna. As the target moves away as each wave crest takes longer to reach the radar. Providing the observer with an accurate depiction of a target’s range and speed is vital for a GSR. Given that a vehicle or a person maybe moving slowly, having accurate Doppler resolution is vital to ensuring that the GSR provides accurate information, the RADA statement notes.
Ground-based air surveillance radars also require high Doppler resolution particularly if being used for fire control to guide a surface-to-air missile to an aerial target where accurate range, velocity and bearing information is vital. Unlike GSRs, they must provide elevation coverage, RADA adds. WLRs, meanwhile, must have a fast-scanning rate. The scanning rate refers to the number of times per minute or per second that a radar looks at a particular area. This is important as artillery, rocket and mortar fire may travel at exceptionally high speeds and may have moved significant distances in the interregnum between each illumination of the ordnance by the radar’s antenna, RADA says. Finally, radars equipping AVSPSs typically only need to cover a comparatively short range, unlike ground-based air surveillance radars, but like WLRs will need to regularly scan a large area around and above the vehicle to detect and track ordnance moving at high speeds.
The physical architecture of a radar also complicates matters: The larger an antenna’s radar that narrower its radar beams will be to provide sharp coverage of an aerial target albeit with a lower scan rate. This is fine for a ground-based air surveillance radar but “less suitable for short ranges requiring wider beams, higher scan rates and elevation coverage,” notes RADA’s statement.
Software Defined Radar
Much like it has in the tactical radio world, the advent of software-defined architecture in the radar world has revolutionised how these systems perform their mission. Software tunes the radar and generates the appropriate waveform according to the task the radar is to perform. For example, if a GSR only needs to be tracking and detecting vehicles and not people, then the operator can simply select this operating mode and the radar’s software does the rest.
Nonetheless, the development of multi-mission radars that can perform all the missions noted in the article’s introduction is not only a matter of overcoming physical hardware limitations like antenna size, but also overhauling the radar’s signal generation and processing. In a nutshell, you are asking one radar to perform a multitude of different tasks at once with different waveforms. A hypothetical true multi-mission radar will need to detect and track all the targets mentioned above simultaneously across a large area. On top of this the radar will have to sort out all the echoes it receives from the targets it illuminates: “These challenges are very complex,” say RADA with the radar having a huge processing burden from the plethora of radar echoes it is receiving from targets. Ultimately, “developing a true multipurpose radar combining all these missions will require a massive development effort before it is feasible,” say Weibel. “One has to apply a certain amount of realism when it comes to the ability to develop a true multi-role radar that solves all tasks equally well all of the time,” Blighter argues.
One possible answer is to deploy radars that can perform a couple of missions, rather than all those listed above, which would still help to reduce procurement and operational costs, and logistics burdens. Weibel says that its Xenta series of X-band (8.5GHz to 10.68GHz) radars can perform several disparate tasks simultaneously including the detection of rotary and fixed-wing aircraft. Equally, the radar can be optimised to detect UAVs, “likewise, we have a RAM functionality that is being refined.”
There is a danger that the hypothetical ‘all seeing radar’ could become not a help but a hinderance: “If a radar could see all types of targets at the same time, it would mean that the operator is provided with too much information, that it would be impossible to digest,” warns Weibel: “How would an operator be able to handle a multitude of target sets and types that have to be potentially engaged with different effectors?”
It may be more practical to use conventional radio communications to network an array of radars on the battlefield and fuse their respective radar pictures together to generate a detailed radar picture of what is happening across the battlefield: “An array of tactical radars, properly connected and synchronised, maybe part of the solution,” RADA says. Blighter believes that this approach could be achieved through the deployment of “lower cost, high-mobility” radars which can “provide a resilient, fused multi-sensor common operating picture.” One potential solution mooted by the firm includes the development of thin and lightweight radars using Active Electronically Scanned Array (AESA) technology where all the radar’s transmit, receive and processing elements are mounted on a single radar tile. These tiles could cover the skin of a vehicle providing surveillance and diverse target detection around the vehicle. The vehicle could share its radar picture to help create this fused picture of the area of operations. The firm cautions that making such radars lightweight and thin enough to equip a vehicle’s skin will be challenging: “Although we are optimistic for the development of such radars, we are mindful that cost and component barriers will provide hurdles for a while yet.”
Furthermore, networking requires bandwidth. There is an inherent danger that networking radars together on the battlefield could tax the bandwidth of deployed communications networks. One possible solution could be to embrace emerging technologies like the secure fifth generation wireless protocols now entering service in the civilian and commercial worlds, and so-called millimetric wave communications in frequencies of 30 gigahertz and above. Both may offer high data rate communications without taxing existing networks. Yet federating these radars takes us back to the same potential dangers that a single multi-mission radar could have vis-à-vis operator overload. Having a single operator monitoring the consolidated radar picture from all these disparate sensors risks the danger that “the human span of control would be exhausted in a very short time,” says Weibel. “It is not only a technological hurdle, but also a human factor hurdle that would need to be handled.”
Vulnerability is a further factor. Like anything on the battlefield that emits RF radars are potential targets for electronic and kinetic attack. One risk for the hypothetical all-seeing radar is that “most battlefield radars are active and so their transmission signature is detectable remotely, rendering them prone to attack and making an all-in-one sensor vulnerable,” warns Blighter. The firm believes that it might be possible to develop a radar capable of handling this quiver of missions simultaneously but that “it is unlikely this would be the optimal solution when looking at all the elements that would need to be factored in for battlefield success.”