If your application uses GNSS, you’re not alone. Legions of hackers, rogue nation-states, and other bad actors are right there with you and your customers, jamming and spoofing the GNSS signals that aviation, defense, and civilian applications rely on.
For example, some jamming attacks target aircraft, from drones to jumbo jets, to prevent them from ascending or descending to the right altitude. This type of attack uses strong RF signals in the GNSS band or adjacent ones to overpower the legitimate satellite signal.
Spoofing attacks use fake GNSS signals to trick the GNSS receiver into believing that it is in a different location or at a different point in time. By relying on these false signals, the receiver provides incorrect timing and positioning data. (For a deeper dive into how spoofing and jamming attacks work, see “Countering GNSS Jamming and Spoofing for Aerospace and Defense Applications.”)
The good news is that device OEMs, systems integrators, and end users have several ways to mitigate GNSS attacks. In the case of spoofing, a powerful new option is Galileo’s Open Service Navigation Message Authentication (OSNMA), which verifies that signals are coming from the Galileo system and have not been modified by a third party. Launched in July 2025, OSNMA is free for use by a wide variety of civilian and other applications.
However, OSNMA isn’t something that can be simply added to an existing device with a software or firmware update. To take full advantage of its cryptographic features and benefits, the device’s hardware must be designed to support OSNMA, starting with its GNSS antenna system. Read on to learn how OSNMA works, why it’s so effective, the key antenna considerations, and how to incorporate it into your device design.
How OSNMA Enables Trust by Verification
One way to think of OSNMA’s role is like a wax seal on an envelope containing an important message. The seal tells the recipient that the letter inside has not been tampered with since it left the sender.
The Galileo Open Service (OS) provides geolocation information in its Navigation Message (I/NAV) broadcast on the E1B signal component. OSNMA certifies that geolocation information by transmitting authentication data in previously reserved fields of the E1 I/NAV message. The navigation data includes the public keys and the digital signature. This architecture means that OSNMA doesn’t create an overlay that would affect OS receiver performance.
Only OSNMA-ready receivers can decode the dedicated I/NAV OSNMA fields. The receivers in devices deployed before OSNMA will continue to function normally because they will ignore OSNMA data. (For more information, download the “Galileo OSMA Info Note.”)
The Antenna’s Critical Role in OSNMA-Enabled Systems
To maximize OSNMA’s cryptographic benefits, the receiver needs a stable, uninterrupted data stream to collect and verify the authentication information. That means the receiver needs a GNSS antenna system capable of providing it with a strong, reliable signal.
When designing an OSNMA-ready device, avoid low-quality GNSS antennas with poor axial ratio or gain patterns, which can introduce phase errors and make the signal more susceptible to corruption. A clean signal is easier to decode reliably. Device designers should focus on antennas with a low, stable axial ratio to ensure consistent signal reception regardless of orientation.
A second key antenna consideration is resistance to interference because OSNMA doesn’t help if the receiver is being jammed. To mitigate that threat, device designers should focus on antenna systems with:
- Multiband Support to provide access to the E1/B1C signals where OSNMA is broadcast.
- High Out-of-Band Rejection with filters that reject cellular (e.g., Band 13) and other RFI that can disrupt the data stream.
- Robust LNA and Filtering to minimize noise and preserve the signal-to-noise ratio (C/N₀), ensuring the data bits are decoded correctly.
Finally, focus on antennas that provide phase center stability. This reduces positioning errors, which is part of the overall “trust” ecosystem.
The bottom line is that antennas play a fundamental, critical role in enabling OSNMA to shift GNSS from a “trust by default” model to “trust by verification.” The receiver handles the cryptographic processes, but it can’t do its job unless it has a high-performance antenna providing the authenticated signal even under the most challenging conditions.
Don’t let your antenna be the weak link in your secure positioning solution. Contact Taoglas’ Engineering team by clicking the button below.
