EW Europe 2018: New Threat Radars Present Intel Challenges

Başlatan Alkyone, Haz 07, 2018, 02:44 ÖS

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EW Europe 2018: New threat radars present intel challenges

Digital radar systems that use new frequency bands and have multifunction capabilities are making it increasingly difficult for electronic intelligence (ELINT) analysts to identify emitters and could soon make current jamming techniques obsolete.

The secretive ELINT world is often a game of cat and mouse between those that want to identify and disrupt emitters through anti-radiation weapons or electronic countermeasures, and the radar operators that want to detect enemy aircraft and neutralise them with anti-aircraft weapons. As countries such as Russia and China build up their electronic warfare capabilities they are developing highly-complex radar systems that can not only detect stealthier aircraft from longer ranges, but also evade detection from equipment designed to map an enemy's electronic capability and order of battle.

For some experts, this duel in the electromagnetic spectrum is currently favouring the radar, especially as many ELINT/ESM systems are not optimised for operating in the frequency bands occupied by emerging radars. That means some radars could go undetected, or a countermeasure is unavailable, which is a risk to personnel. Challenges include the renewed development of digitised VHF radars, operating in the lower 150MHz spectrum, which were once considered obsolete until it was realised they could track stealth aircraft.

'This is a major issue for [electronic support measures] receivers, they tend to start at 2Ghz, so these are pretty much invisible,' said Nigel Lawton, a former Royal Navy ELINT specialist and now ELINT and radar-ESM systems product manager at German EW specialist Rohde and Schwarz.

Digital VHF radars continue to be developed with China showcasing an AESA VHF/UHF radar at the 2016 Zhuhai Air Show known as the JY-26 Skywatcher-U. Developed by the 14th Institute (Nanjing Research Institute of Electronics Technology, or NRIET), the radar reportedly has a 500km detection range and has been able to track F-22 stealth fighters operating over South Korea.

Radars are also being developed that emit in the high-frequency K-Band or higher, generally between 33-36Ghz. 'You're finding that more radars are moving up the band, so that's very difficult for us as collectors to intercept these radars and radar designers know this,' Lawton said. To intercept a K-Band radar often needs an ELINT collector to actually see the radar, which is dangerous for operators if the sensor is connected to a gun or missile as part of a defensive weapon system.

Unlike previous generation radars, today's sensors also emit just enough power to detect the target and do not radiate more energy than required. Multifunction radars operating in the 2Ghz range, for instance, are increasingly difficult to intercept and analyse as they employ more sophisticated low probability of intercept (LPI) features. Ultimately, according to Lawton, the proliferation of these complex radars means it can now take ELINT operators months to put a profile together for a database.

Lawton singled out Frequency Modulated Continuous Wave (FMCW) radars as particularly troublesome. 'The problem is the power is spread through the spectrum, it's just noise, so unless I can see this radar as early as possible in processing chain I will not intercept and I certainly cannot process it with conventional ESM processes.'

Legacy mechanically scanned radars were relatively easy to collect and analyse, with ELINT operators able to look at the pulse repetition frequency (PRF) to identify the radar and ultimately jam it. These systems would use magnetrons or travelling wave tubes that could be 'fingerprinted' by ELINT systems. That has fundamentally changed with today's digital active or passive electronically-scanned technologies, which can adapt radar pulses to the environment. These systems can cycle through different modes - including acquisition, target tracking and target illumination - in one time period, allowing multi-mode operations simultaneously.

'That's a major problem if you have a wide open receiver…if that waveform doesn't change I don't know what he is doing' said Lawton. 'And how do you jam [a multi-mode radar]? I have no idea. I think jamming may be obsolete in the next few years.'
Many modern ELINT/ESM systems are no longer sensitive enough, and wideband receivers are often 'blocked' by radar emitters that can push out two simultaneous high-power pulses. Narrow band receivers also present challenges, mainly a lower probability of intercept and not addressing the growing bandwidth of radars. Rohde & Schwarz has developed a two-stage detection process for its systems such as the WPU 500 wideband processing unit, which includes a pre-processing phase. This means that it is optimised to detect complex, low-power threats such as solid-state and FMCW radars.

'We are looking into the spectrum before we are processing the radar,' said Lawton. 'If you were to process the radar and you want to analyse it, you need to get 12-13dBs above noise. So a low-power radar that does not give me that signal-to-noise ratio will not produce good pulses that I can analyse.'
'What we do, we match the processing bandwidth to the bandwidth of the transmitting radar…we see the radar before we process, we see the bandwidth of the radar on the frequency, once you know the bandwidth I can put my processing channel exactly around the bandwidth of the transmitted radar.'   
This, along with other advances in the ELINT world, could give operators their edge back over the new-generation of advanced radars, but for how long?

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