Advancements in anti-jamming GNSS antennas
The modern world is ever more reliant on the Precision Navigation and Timing (PNT) services delivered by GNSS satellite constellations. The global coverage of GNSS, combined with its accuracy, is driving its adoption by an expanding range of applications and, as technological advancements increase, the availability of powerful, low-cost receivers, GNSS has become dominant wherever precise positioning and timing are essential.
The growing dependence on GNSS is accompanied by an increased awareness of its vulnerabilities and the attendant risks to global services and infrastructure. Spoofing and jamming attacks in particular are on the increase, and developers of GNSS systems are increasingly focused on combating these twin threats. This article discusses common jamming techniques before describing anti-jamming solutions and the crucial role that RF antennas play in defending against jamming attacks.
The economic benefits of GNSS
GNSS services contribute significantly to the global economy, with a 2019 study estimating that US private sector industries had accumulated US$ 1.4 trillion in economic benefits since GPS was first made available to them in the 1980s. A more recent study, commissioned in 2023 by the UK government, put the country’s economic benefits from GNSS at £13,622 million per annum (Figure 1), with the majority gained by the emergency services and the roads sector.
Figure 1: Share of economic benefits by sector (UK).
These growing benefits are accompanied by a corresponding increase in the risks associated with the loss of this critical infrastructure. By the time GNSS signals arrive at the Earth’s surface, their power is significantly lower than ambient noise levels, and receivers can easily be overwhelmed by more powerful transmissions within, or adjacent to, their frequency bands. While this interference may be unintentional, caused by factors including spectral overcrowding or site-based interference, deliberate attempts to disrupt GNSS services by malicious agents are on the rise. Such disruption can have severe and, in the case of applications such as autonomous driving, potentially life-threatening consequences. For industries including agriculture and construction, which rely on GNSS for precision guidance, positioning errors can have significant economic consequences, impacting crop yields, project timelines and overall profitability. Similarly, the loss of timing signals can critically impact communication networks and energy infrastructure, leading to financial losses and disruption to mission-critical services. The above UK study puts the financial impact on the UK of a seven-day loss of GNSS at £7,644 million, while the cost to the US economy of a single-day outage was estimated at around US$ 1 billion. [3]
Spoofing and jamming attacks
The growing dependence on GNSS has been accompanied by an increased threat of deliberate disruption, through spoofing or jamming attacks. Spoofing is an intelligent form of interference where false GNSS signals are transmitted in an attempt to make GNSS receivers believe they are at a different location. Spoofing attacks are considered the more dangerous form of malicious attack, since they can often go undetected, but are relatively more difficult to generate.
Jamming attacks, on the other hand, can be launched using cheap, readily available devices. GPS jamming has been on the increase since 2016, with the eastern Mediterranean, Black Sea, areas of the Baltic, Poland, and parts of Scandinavia the world’s most heavily jammed areas in 2024 (Figure 2).
Figure 2: Global jamming hotspots. Source: https://gpsjam.org/?lat=44.17986&lon=44.89385&z=2.8&date=2024-03-13. Image courtesy of GPSJAM, https://gpsjam.org [4].
Jamming techniques
Jamming involves transmitting an RF signal which exceeds the threshold of the GNSS receiver, effectively raising the noise floor and making it impossible for the receiver to distinguish between the satellite signal and the jamming signal. Receivers with poor sensitivity are more easily overwhelmed by strong jamming signals. Various types of RF signal can be emitted by the jammer.
Out-of-band jamming occurs when the jamming signal is transmitted outside of the target band, with the strong jamming signal spilling over into the GNSS band, causing interference and disrupting the receiver, or simply overdriving the receiver. With in-band jamming, the jamming signal is transmitted within the satellite frequency bands (L1, L2, L5) and is strong enough to overpower the weaker GNSS signal. In-band jamming is impossible to filter out, but out-of-band jamming might be overcome with adequate filtering.
Continuous Wavelength (CW) jamming is the most straightforward jamming method, where the full power of the jamming signal is concentrated into a single frequency, blocking anything else being transmitted on the same wavelength. Since modern receivers can overcome CW attacks using notch filters, attackers can also use sweep modulation techniques, where several CWs are transmitted sequentially, at alternating frequencies, increasing the effectiveness of the transmitted signal. Jammers can also use barrage techniques, transmitting a burst of narrow-band signals, one after the other, creating noise across the entire, or partial width of the targeted GNSS band.
Directional precision helps improve jamming attacks, and jamming devices can be found on the market which resemble guns, using a directional antenna, designed to precisely aim at a specific target. Although it is illegal to operate jamming equipment in most countries, including the USA and the UK, it is not difficult for an individual to acquire a jamming device, and an internet search will reveal a wide spectrum of devices available to purchase online. Small jammers, capable of transmitting at 1 Watt, are around the size of a cigarette packet, while larger, VCR-sized devices can transmit at up to 100 Watts. To put this into context, jammers used in the military conflict in Ukraine are usually around the size of a truck and transmit at around 1 kW.
Deliberate jamming, once a specialist military activity, is now available to anyone who can buy or build a signal jammer.
GNSS anti-jamming strategies and techniques
Designers of GNSS receivers have access to multiple strategies when combating jamming, including:
- Nulling systems, which generate a “null” in the direction of the jamming signal. If more than one jamming signal is present, multiple nulls can be generated in the direction of each jammer.
- Beamforming, where a “beam,” or RF pattern, is directed towards a known GNSS satellite, reducing the chance of interference, since any jamming signal would need to be coming from the exact direction of the known satellite.
- Excision, which eliminates any narrowband signal exceeding defined thresholds. Any signal exceeding these thresholds is eliminated, leaving the remaining signals to be transformed for “nulling” – described above.
As the first component of the receiver to process the satellite signals, the GNSS antenna plays a key role in anti-jamming, and therefore correct choice and installation of the antenna is crucial. If the antenna saturates, for example, the first line of defense fails, and the receiver will be unable to correct the GNSS signal.
Active antennas, which include embedded filtering such as surface acoustic wave (SAW) or ceramic, are effective against out-of-band jamming, maximizing gain within the GNSS band while attenuating signals outside it.
Whereas traditional GPS antennas are often omnidirectional, anti-jamming antennas focus on a specific direction of known GNSS satellites, reducing reception of the transmitted jamming signals. Controlled reception pattern antennas (CRPA) combine multiple antenna elements, spaced a known distance apart, in an adaptive antenna array. When combined with signal-processing techniques, this array can determine the direction of arrival of the jamming signal, enabling the radiation pattern of the antenna to be adapted, creating lower gain or “nulls” pointing in the direction of the jamming signal (Figure 3). CRPAs are highly effective at mitigating all types of interference, including in-band jamming, although a CRPA system needs sufficient antenna elements to counter each jamming signal.
Figure 3: Typical radiation pattern and radiation pattern with a null.
Antenna systems that support multiple GNSS bands and multiple constellations offer a level of diversity, which can provide alternatives when the primary GNSS signal is jammed. Sophisticated, multiband GNSS receivers can be combined with CRPAs to counteract multiple jamming attacks by independently nulling different GNSS bands.
Designing CPRAs and multiband antenna systems requires specialist knowledge and testing tools and can add significant time, complexity and cost to development cycles of GNSS receivers. Companies that specialize in antenna design, such as Taoglas, can significantly accelerate time to market by providing off-the-shelf devices, coupled with in-depth support and customization services.
Potential future developments in anti-jamming technology
Threats to GNSS signals are becoming increasingly sophisticated, requiring a constant focus on the development and implementation of advanced anti-jamming solutions. The military and government sectors are behind much of the research and development of anti-jamming technologies, with initiatives including:
- Advanced signal processing algorithms designed to improve anti-jamming performance.
- The development of compact, integrated anti-jamming solutions which integrate multi-element antenna arrays and signal processing in a single unit.
- The development of jam-resistant satellite communication (SATCOM) systems.
- Improvements in satellites, delivering more power to increase resistance to jamming.
As GNSS technology continues to evolve and becomes increasingly integrated with mission critical systems, the development of robust anti-jamming solutions will remain a priority to ensure its long-term integrity.
Author biography
Patrick Frank is an RF and Antenna Engineer at Taoglas with over 15 years of experience in the wireless industry. He holds a Bachelor of Science in Electrical Engineering (BSEE) from Minnesota State University.
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