Team from Xidian University say they have used their mobile device to track civilian aircraft, with the data suggesting the technology works
Several research projects in China are focused on anti-stealth radar advances, including developing quantum radar technology

Chinese researchers say they have been tracking F-22 jets using anti-stealth radar technology since 2013. Photo: AFP

Scientists in western China have developed an anti-stealth radar so small it could be quietly and easily set up almost anywhere, including on a rooftop, according to the research team behind the project.

Anti-stealth radar systems usually require a large antenna to pick up the weak signature of stealth aircraft equipped with technology to absorb or deflect radar signals.

“Although the detection accuracy of the radar can be improved by increasing the antenna aperture, it will reduce the mobility and survivability of the radar platform,” said professor Yang Minglei in a paper published in the domestic peer-reviewed journal Modern Radar on August 11.

The metric wave radar array developed by Yang, of the national laboratory of radar signal processing at Xidian University, Xian, and his colleagues, is similar in size and appearance to a clothes-drying rack, according to a photo published in the journal.

The researchers said the mobile device showed superior performance in detection accuracy and range in a number of tests conducted on the roof of a university campus building.

China has a multilayered air-defence system with anti-stealth radar stations, especially along the eastern Pacific Ocean and the South China Sea coastline.
According to a public presentation in 2018 by Wu Jianqi, a lead scientist in the military’s anti-stealth radar programme, Chinese radar systems could detect and track American F-22 jets – regarded as the world’s most advanced and powerful stealth fighters – flying several hundred kilometres off the Chinese coast as early as 2013.

The coating and structure of stealth aircraft can weaken or redirect high frequency millimetre-long radio waves.

But the Chinese anti-stealth radar uses waves at much lower frequencies that are longer than a metre (3.3 feet). These low-frequency waves could interact with the stealth aircraft’s large components, such as its wings or tail, to produce echo signals more than 100 times stronger than those of military radar that operate at higher frequencies, according to Wu.
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Most metric wave radar systems are huge. Even mobile versions can be tens of metres high when fully extended. The devices usually need to be towed by large trucks and take hours to set up, making them easy targets for satellites and drones.
The anti-stealth detection device can be mounted on a rooftop. Image: National Laboratory of Radar Signal Processing, Xidian University, Shaanxi province

In 2019, the Israeli air force destroyed a Chinese-made JY-27 metric wave radar in Syria. Although the device was believed to be a watered-down version of those used by the People’s Liberation Army, the incident heightened concerns about how well these anti-stealth platforms can survive.

Radar satellites can detect objects that conventional satellites cannot see. Photo: Shutterstock

A team of Chinese military researchers said that they have developed an invisibility cloak that can hide ground military targets from spy radar satellites.

Hiding objects from advanced military radars is difficult because they can detect weapons or infrastructure that are invisible to normal cameras and can identify items no bigger than a shoebox from space.

Unlike a telescope satellite that works only in day time, radar satellites can also produce crystal-clear photos at night.

The new device, produced by a team at the Air Force Engineering University in Xian, Shaanxi province, is a piece of cloth that can be stretched to fit almost perfectly over a wide range of different items such as tanks, artillery or radar stations.

It is this unusual flexibility that can help make the object near-invisible even to radar satellites, according to lead researcher Xu Hexiu and his team.

They wrote that a target wearing the cloak would appear like “a piece of land with nothing on it” in a paper published in the Journal of Infrared and Millimetre Waves last month.

Technology already exists to mask stealth fighters and other warplanes from radar, but it does not work on the ground because radar signals bounce back after making contact with the land.

This means that of objects such as tanks that are coated with the materials used on stealth fighters – which either absorb radar signals or use geometric structures to deflect radio waves – would stand out because they form an unnatural contrast to their background.
The invisibility cloak is made from thin layers of material, including circuits that disrupt the radar signal. Photo: Air Force Engineering University

But Xu and his colleagues argued that another way is to change the signal pattern so that it resembles that produced by a natural landscape.

The invisibility cloak has several layers. On the top is a thin fabric carrying many printed circuits that can manipulate electromagnetic waves.

Xu’s team used a unique 3D-print technology that could draw the circuits on a soft piece of fabric as thin as a strand of human hair with extremely high precision.

The researchers then added more layers, including plastic and thin metals, to make what they called a “meta surface” that can change the direction of a return signal to mimic the radar signature of flat land.

Numerous metamaterials have been developed to cheat a radar satellite, according to Xu, but none can move as freely and extensively as the new cloak.

When radar waves hit an uneven object, they bounce back in various directions allowing a computer to work out its size and shape by measuring the differences in the signal.

But when the researchers tested the performance of the device in a simulation facility, the waves that hit the cloak returned in a uniform pattern similar to that from flat lands.

The greater the distance from the radar to the target, the less disturbance could be detected.

The scientists also said the technology can counter the effect of satellite radars changing the strength and angle of their beams to reveal more details about a target.

According to an estimate based on real world data, camouflage technology can protect more than 80 per cent of the military targets from being destroyed by missiles, according to a radar scientist from the Beijing Institute of Technology who asked not to be named because he was involved in a military programme.

But the device developed by Xu’s team does not work as a stand-alone item like something from science fiction or the invisibility cloak in Harry Potter, said the researcher.

“It needs to work with other methods including heat reduction, optical camouflage and decoys to achieve the desired effects,” he said.