The tiny lens antenna with big potential

Living in a satellite world

From finding our way around a new city to delivering medical help to those in need, satellite navigation has become an essential part of our daily lives. However, our dependence on this technology makes it an obvious target for malicious actors, who can disrupt it in multiple ways.

The most common is ‘jamming’, when receivers are overwhelmed with signals that clog the airways, making them unable to function properly, and ‘spoofing’, when fake signals are sent to mislead a receiver. During a spoofing attack, your smartwatch might show the wrong time, or your maps app might say you are kilometres away from your actual location.

To mitigate these threats, the European Space Agency (ESA) is exploring new ways to protect satellite navigation systems, as well as identifying which technologies perform the best against interference.

Going round

ESA navigation engineers propose a solution that builds on technology which has existed for over half a decade: a spherical lens antenna.

Noori Bni Lam, ESA’s radio navigation engineer, explains: “In the context of antennas, a lens is a plastic ball that can focus or bend radio waves, just like an optical lens does for light.

“We focused on a specific type of lens – called the Luneburg lens – which is spherical and made up of layers that have different densities. The outermost layers are the least dense, while the core is the densest.”

“Because the lens is symmetrical by nature, it can steer a signal beam coming from the antenna underneath it in almost any direction, making the antenna capable of receiving signal from any satellite,” adds Lionel Tombakdjian, research engineer at Université Côte d’Azur in France. During his PhD research project with ESA’s Navigation Laboratory, he explored ways to make this technology cheaper and easier to manufacture.

“While a Luneburg lens is not specifically designed to mitigate jamming and spoofing, its inherent beamforming properties naturally provide a degree of resilience in certain interference scenarios,” mentions David Gomez Casco, ESA’s navigation systems engineer.

“Because the lens forms several narrow beams that each point in a different direction, the beams that are not facing the jammer – the device emitting disruptive signals – naturally receive much less of its power. As a result, some beams are far less affected by the jammer, allowing the receiver to pick up the real satellite signals more clearly.

“In addition, the ability to focus on a specific direction allow Luneburg lenses to receive stronger and clearer signals. This helps reduce the reflections of signals off nearby surfaces, which is a common source of positioning errors.”

Printing a magic ball

While the properties of Luneburg lenses make them uniquely suited for navigation applications, any attempts at manufacturing them so far have been too expensive and resulted in bulky and complex structures.

That is where Lionel’s research comes in.

“In my project, I designed, 3D printed and tested a Luneburg lens made of plastic, specifically polylactic acid (PLA), which is the most commonly used 3D printing material,” says Lionel. “Although PLA has its limitations, these first successful 3D printing attempts opened a path to a flexible, low-cost solution for real-world satellite navigation applications.”

Since it was made in 2024, ESA engineers have already brought the 3D-printed lens twice to Jammertest – the world’s largest open air testing campaign for jamming and spoofing resilience, organised every year on the remote island of Andøya, Norway.

David adds: “In addition to providing a degree of resilience against jamming and spoofing, the structural properties and beamforming abilities of the lens make it suitable for use in very high latitudes where satellites pass relatively low above the horizon. In these conditions, the lens can offer additional benefits by forming beams that point towards the regions of the sky where satellites are actually visible.”

“The study of the Luneburg lens for navigation began as a small exploratory contract to expand ESA’s Navigation Laboratory equipment, yet it quickly demonstrated strong potential as a promising technology for satellite navigation applications,” adds Paolo Crosta, ESA’s Head of Navigation System Implementation & Validation Section.

“The core idea behind the design was to generate multiple simultaneous beams, each pointing toward a different region of the sky, thereby improving signal reception and robustness. We immediately saw that the lens had very high potential for navigation because it simplifies the receiver’s processing and can be scalable with respect to new emerging constellations and different frequency bands.”