Jamming Techniques Share Common Goals

2020-02-29  |  5 min read 

Through the continuous, fast-paced changes in technology, jamming remains a major threat for military systems. As threats grow in sophistication, countermeasures evolve at or beyond that pace. In radars, for example, every evolution brings more complexity. Yet countermeasures achieve that same complexity and potentially move beyond it. In this game of cat and mouse, jamming techniques continue to evolve. To understand how they work, however, one can look at some well-known approaches.

Broadband noise is an example of a simple jamming technique. Think of an RF receiver. Radar works by sending out a pulse, which reflects off things in the environment and bounces back. If you send out a pulse in the air where an F-35 is flying, RF energy bounces off that F-35, returns to the radar receiver, and you see the return. That’s called an echo return or a skin return of a platform.

Potentially, the simplest way that you can undermine a radar is by jamming it with broadband noise. At the same time at which that skin or echo return hits the receiver, you can send RF energy into the receiver. The skin return is not detectable because they can only see this huge amount of energy.

With jamming techniques like range gate and velocity gate pull offs, you take this one step further by sending a pulse back that looks like the skin return, but changes it slightly. As a result, the object off which the reflection is sent appears to be moving in a different direction so you lose tracking on it. In the example of an aircraft, this approach makes it seem like it’s flying in a direction other than its true course.

Another well-known jamming method is digital radio frequency memory (DRFM). It comprises taking in the RF signals, digitizing them, and turning them around to create new RF energy based on the pulse received. Because this approach has a very fast turnaround time, it can be used to create multiple false targets.

Running through these approaches is the goal of creating confusion around the true target – whether it is there at all or, if it will be detected, misconstruing its location or number. With stealth technology, for example, radar sends out a pulse but cannot get a good skin return. Due to the design of the fighters and bombers and the materials – which do not reflect RF energy well – the radar struggles to detect them.

Last fall, however, an article from The National Interest indicated that stealth in particular may soon prove obsolete. The state-owned China Electronics Technology Group Corp. announced that it had created a practical meter wave sparse array synthetic impulse and aperture radar. It claims that its multiple transmitting and receiving antennas — tens of meters high, scattered in a range of tens to hundreds of meters — can continuously cover the sky as the radar receives echoes from all directions. According to the article, the radar can supposedly track an aerial target and identify a stealth aircraft’s exact coordinates.

Whether technologies have truly found a way to take advantage of stealth’s vulnerability to low-frequency beams, the fact is that EW developments– and ways to overcome them – will eventually be surpassed by new, more effective methods. EW techniques continue on a fast path of evolution, thanks to developments like software-defined radio and machine learning. All of these efforts have the same goal: to characterize and exploit the operational environment to increase understanding, deny access to adversaries, and expand the maneuver space. Success in these areas provides a lead in the EW cat and mouse challenge.

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