An unprecedented radar experiment conducted by Chinese scientists in the South China Sea could change the game of future warfare.

Taking a DJI Phantom 4 Pro drone – about the size of a bird and with a radar cross-section comparable to that of a stealth fighter – the team launched it off the coast of Guangdong.

The ground-based radar did not sent out any radio waves to produce an echo, but the target appeared on screen. This was because the drone was illuminated by electromagnetic radiations emitted by a Starlink satellite flying over the Philippines, according to the scientists.

No other country has demonstrated this capability before.

Stealth aircraft, such as America’s F-22, reduce electromagnetic wave reflection through geometric shapes and absorbing coatings to cheat radars.

 

However, if a radar station can make use of the Starlink satellite signals – which are strong and almost everywhere – its detection capabilities could be “unaffected by the target’s three-dimensional shape and surface material”, wrote the research team led by Professor Yi Jianxin, with the school of electronic information at Wuhan University, in a paper published on August 26 in the Journal of Signal Processing.

This will “provide significant advantages in detecting small and stealth targets”, they said.

Also, ordinary military radars reveal their positions when operating, making them potential targets for enemies.

“By using third-party radiation sources, radar systems can have enhanced concealment and anti-jamming capabilities,” Yi and his colleagues wrote.

The experiment was supervised by the Chinese government’s State Radio Monitoring Centre, and the results were peer-reviewed before publication.

When an aircraft passes through the airspace between communication satellites and ground antennas, it can scatter some of the electromagnetic waves emitted by the satellites.

These waves, also known as forward scatter, can disturb normal communication signals.

Scientists can analyse these small disturbances to identify and track a target of interest.

 

The idea of using forward scatter to detect drones was first proposed by Russian scientists at an international academic conference in 2015. But Starlink did not exist at that time.

Today, this giant constellation built by SpaceX has more than 6,000 satellites, constantly emitting high-frequency radio signals to support internet connections up to 220Mbps.

This complex electromagnetic environment was not considered in the design of current stealth fighters several decades ago.

SpaceX’s Starlink cooperates closely with the US military and has played a significant role in the Russia-Ukraine conflict. Researchers in the Chinese military are developing technologies to destroy Starlink if necessary.

But some teams are instead looking at how Starlink can be turned against the US military.

“Low-orbit satellite signals have the advantages of [being] all-weather, cross-regional and low-cost, which can be perfectly combined with covert forward scatter radars,” Yi’s team wrote.

The Starlink signals are encrypted, and SpaceX founder Elon Musk does not provide services for Chinese users.

However, Yi’s team claims that they can build a Starlink receiver using inexpensive components easily available in the electronics market.

The antenna is fixed on a rotatable base, allowing it to track the satellite moving across the sky.

Before this study, scientists had used FM radio, digital television and even hostile military radar signals to detect large targets such as civil airliners and cargo ships.

However, detecting small or stealth targets is much more challenging.

Yi and his colleagues revised the model of forward scatter radar detection based on a deeper look at the fundamental physical mechanisms, and they developed a new algorithm.

They also used an undisclosed high-performance chip to process the received signals.

Currently, their radar antenna is only the size of a frying pan, and the drones in the experiment flew at relatively low altitudes. Therefore, the technology disclosed in the paper cannot be directly applied to military use.

But Yi’s team claims they successfully detected signals corresponding to detailed features such as drone rotor movement, confirming the “feasibility and effectiveness” of the method and system design in anti-drone and stealth fighter applications.

China uses various methods to detect stealth aircraft to enhance its regional denial capabilities.

These methods include using large-scale Earth observation satellite constellations to automatically identify and track flying US stealth fighters, and deploying over-the-horizon radars along the coast which emit long-wave detection signals that cannot be absorbed by stealth coatings.

To prevent US military intervention in the South China Sea and Taiwan, the Chinese military has also installed advanced anti-stealth radars on many warships to form an electronic warfare killing network, according to state media reports.