What is CRPA Antenna ?

CRPA means Controlled Reception Pattern Antenna. Controlled reception pattern antennas (CRPA) are active antennas that are designed to resist gps jamming and spoofing. They are generally used in navigation applications for UAV,Drones, Aircrafts etc.

Currently, at so many places across the world, militaries are jamming and spoofing GPS signals. CRPA antennas are generally designed to improve the reliability and accuracy of GPS and GNSS signals in jammed and spoofed environments. These antennas dynamically adjust their reception pattern to mitigate interference and jamming, ensuring robust signal reception. By enhancing GPS and GNSS signal integrity, these antennas enable drones and autonomous vehicles to operate effectively, even in spoofed or signal-jammed areas.

What is PNT ?

PNT Stands for  position, navigation, and timing (PNT). It is the service capable of providing an absolute position and autonomous time, global navigation satellite system (GNSS) signals are a key input to the multi-sensor positioning systems used by aerospace, defense, autonomous vehicles, advanced driver assist systems (ADAS), and other safety- and reliability-critical systems.

For developers, designers, and integrators of those systems, protecting the GNSS receiver against radio frequency (RF) signal interference is a key important thing. It’s an area where specialized anti-jam CRPA antennas can play an important role, but choosing which one and effectively integrating it presents a challenge.

New Warfare Domains

While all natural forms of RF interference like solar storms and ionospheric scintillation are well known, artificial NAVWAR threats such as signal jamming and spoofing, as well as adjacent-band interference (ABI), are continually increasing in prevalence, diversity, and sophistication. These are the new age domains of warfare. Without mitigation, they can significantly affect a receiver’s ability to compute an accurate position.

One way of countering these threats is to use a specialized CRPA antenna capable of rejecting interference waveforms and focusing on origianl GNSS signals. Such anti-jamming and anti-spoofing antennas are designed to provide increased interference protection at the receiver’s RF front-end by maximizing antenna gain towards genuine GNSS signals and/or minimizing gain towards interfering signals.

There has been latest discussion and experimentation with regard to modifying fixed reception pattern antennas (FRPAs) to enhance anti-jam capabilities – including using choke rings and shaped ground planes – but currently lets focus here on CRPAs.

Working of CRPA Antenna ?

A CRPA employs multiple physical antenna elements whose reception pattern can be dynamically adjusted by the receiver in response to interference signals detected in the environment. Because of this ability to detect and respond to interference, CRPAs are sometimes also called adaptive antennas.

CRPA designs vary, but typically include multiple individually controllable antenna elements arranged in a circular pattern around a central reference element. Signal processing algorithms detect interference signals and amplitude and phase from each antenna element are adjusted in real-time to either to form a null in the direction of the interference source (null steering), or to direct the peaks towards genuine signals (beam steering).

CRPAs can offer strong protection against interference, especially when paired with sophisticated interference detection and mitigation algorithms, but their large form factor can be prohibitive for smaller devices and devices where weight is a key consideration. They also consume more power than a FRPA and can be expensive, so making the right decision is critical.

Atom Anti jamming GNSS antenna for FPV/UAV

Atom Drones FPV Anti Jamming Module for Stable Drone Navigation

FPV Anti Jamming Module technology plays a critical role in maintaining accurate navigation during modern drone operations.
In interference-heavy environments, reliable GNSS positioning is essential for safe and predictable FPV flight.
Therefore, this GNSS anti-jamming module is engineered to protect navigation signals from intentional and unintentional interference.
Instead of relying on basic signal filtering, it uses advanced multi-band GNSS processing to ensure continuous and stable positioning.
As a result, FPV pilots gain improved control, situational awareness, and confidence during flight missions.

Atom FPV Anti Jamming CRPA Antenna Module with Multi-Band GNSS Signal Protection

At the core of this navigation protection module, support for multiple satellite constellations including GPS, BDS, and GLONASS enables wide-band signal reception.
Because these GNSS systems are processed simultaneously, positioning accuracy remains consistent even when individual signals are degraded.
Consequently, reliable navigation is maintained under jamming, obstruction, or multipath conditions.
Moreover, deep-coupled navigation algorithms further enhance resistance to signal distortion in complex RF environments.

Where are anti-jam CRPA antennas typically used?

Anti-jam antennas are typically used in GNSS receivers where either the equipment itself or a downstream application that relies on its PNT information requires high levels of protection against GNSS interference. Systems that would benefit from incorporating CRPAs include:

• Military Drones vehicles and equipment: CRPAs originated in the military domain with the need to protect vehicles and equipment against adversarial jamming and spoofing, key tactics used in electronic warfare and NAVWAR. CRPAs can also protect military receivers against Blue Force Electronic Attack (BFEA) waveforms, a type of selective jamming used to disrupt enemy access to GPS signals.
• Critical National Infrastructure (CNI): CNI – including power and utility grids, mobile base stations, stock exchanges, and more – has an increasing and increasingly critical dependence on timing data derived from GNSS. Lower cost CRPAs have been proposed to protect these important functions from the growing threat of RF interference.
• Autonomous vehicles (AVs): Self-driving vehicles require advanced protection against harmful interference to GNSS receivers to ensure they can position themselves with a high degree of accuracy and navigate accurately and safely at all times. GNSS is frequently used as the ‘truth’ signal within a multi-sensor AV positioning system, both to determine an absolute position and to discipline inertial sensors prone to drifting, so protection against jamming and spoofing is essential. Whether or not CRPAs become commonplace in civil autonomous vehicles will likely be decided by cost and regulation as the technology matures.
• Commercial aircraft: Civil aviation is increasingly subjected to jamming and spoofing attacks. As more nation states bring these tactics into their defensive and offensive arsenals, this problem will only increase. Similarly to autonomous vehicles, whether or not CRPAs are leaned on to solve this problem will likely depend on regulatory aspects such as export controls, and physical aspects such as size, weight, power and cost.

What kinds of interference can CRPAs protect against?

CRPAs are designed to protect GNSS receivers against multiple types of RF interference. It should be noted that they can’t always be relied upon to provide 100% protection, and therefore should be used as one element in a layered approach to PNT hardening.

However, the types of interference they can help to protect against include:

• Jamming: Intentional GNSS frequency jamming is a widespread threat, often caused by illegal jammers used to override vehicle telematics or by nation states engaging in electronic warfare. It works by flooding the RF environment with waveforms that ‘drown out’ the faint signals from GNSS satellites. Unprotected receivers may lose lock or output an inaccurate position without warning.
• Adjacent-band interference (ABI): This refers to unintentional interference from radio transmissions in bands close to the GNSS frequencies. It can stem from faulty equipment emitting signals on the wrong frequency or from legitimate services operating in spectrum bands close to the GNSS bands. As with intentional jamming, ABI can cause loss of lock or degraded positioning accuracy.
• Spoofing: The intentional transmission of fake GNSS signals has become easier with the rise of software-defined radio (SDR). Spoofed signals can cause the GNSS receiver to compute an erroneous position and time and the equipment to behave erratically as a result. Spoofing attacks on military equipment or critical national infrastructure (CNI) are becoming a more frequent tactic in electronic warfare.
• Multipath: In built-up areas, GNSS signals tend to reflect off buildings and other objects in the environment. These signals have slightly further to travel, and so arrive at the receiver slightly later than line-of-sight signals. Without mitigation, multipath interference can cause the receiver to calculate an inaccurate range measurement, which translates into an inaccurate position output.
• Obscuration: GNSS signals work on a line-of-sight basis and are often blocked by buildings, hillsides, and dense foliage. An unprotected receiver can be especially vulnerable to jamming and spoofing attacks in areas of high signal obscuration or when exiting a GNSS-denied area like a tunnel or underground car park. As the receiver attempts to reacquire a signal, it can be subjected to a spoofing attack, causing it to lock on to the fake signal rather than a genuine one.

White paper: Fundamentals of GNSS threats

This white paper provides an introduction to GNSS threats and vulnerabilities, from ionospheric scintillation to jamming, spoofing, and multipath.

Read the white paper

Evaluating CRPAs and other types of anti-jam GNSS antenna

Anti-jam antennas can vary significantly in cost, form factor, and functionality. To evaluate whether your device or system needs one, and if so, which one it needs, the key considerations are the function of the device or system and the type and amount of interference it’s expected to encounter.

Typically, anti-jam antennas are used in systems where continuous, accurate, and reliable GNSS-derived PNT is a non-negotiable requirement — that is, where a loss of GNSS availability or signal integrity could result in a serious safety issue, mission failure, or significant loss of business.

Due to their cost, size, and complexity, anti-jam antennas also tend to be limited to systems that are not only mission-critical, but are also likely to encounter frequent harmful interference, potentially of multiple different kinds. A thorough risk assessment should form part of the decision-making process when evaluating what type of antenna and receiver system to incorporate.

For the majority of safety- and mission-critical systems, a CRPA antenna will be the clear choice. The level of robustness added and the ability to enhance performance even when interference is not present make it the most powerful enhancement to GNSS.

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White paper: Characterizing CRPA Antenna and other adaptive antennas

This white paper takes a deep dive into evaluating, selecting, and testing CRPAs and other adaptive GNSS antennas for developers, integrators, and buyers of mission-critical PNT systems.

Read the white paper

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How to test the performance of CRPAs

CRPAs must be thoroughly tested to ensure they perform as expected in different types of interference conditions.

While testing outdoors in a live sky environment is possible, it can only be done on certified test ranges with the right permissions and equipment. The logistics of setting up the test range and obtaining authorization to transmit interference signals make outdoor testing very expensive and something that typically only happens in the final verification stages of product development.

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Video: Quick guide to CRPA testing

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At earlier stages of receiver R&D and integration testing, lab-based simulation equipment is used to transmit GNSS signals and interference waveforms to the device under test (DUT). Lab testing of receivers that use CRPAs can be carried out in two ways:

Conducted testing: This involves playing simulated GNSS signals and interference to the receiver (or antenna electronics unit for a CRPA) via coaxial cable, bypassing the physical antenna. This kind of testing is used to test the receiver system as a whole at the R&D stage. However, because the signals are conducted directly to the receiver, it doesn’t test the performance of the antenna hardware.

Radiative or over-the-air (OTA) testing: This involves transmitting real or simulated RF signals over the air to the DUT to evaluate the performance of the antenna and antenna electronics. This kind of testing is typically carried out later in the product cycle to validate the performance of the whole system including the physical antenna subsystem.

Because of the need to isolate simulated GNSS signals and interference waveforms, lab-based OTA testing must take place in a closed (anechoic) chamber. The chamber can be configured in different ways, from using traditional fixed broadcast antennas in static scenarios, to using a more sophisticated ‘zoned chamber’ setup to simulate satellite movement in orbit.

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Video: Using a zoned chamber for advanced CRPA testing

Spirent’s Steve Hickling presents a quick guide to over-the-air testing of CRPAs using a zoned chamber approach for longer and more realistic test scenarios.

Watch video

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Solutions for CRPA testing

Atom Drones offers a full suite of solutions to support both lab-based and field-based testing of CRPAs and other types of anti-jam GNSS antenna. Our solutions include:

• GNSS & wavefront simulation: Atom PNT X produces a comprehensive range of emulated multi-GNSS, multi-frequency RF signals, including classified signals such as GPS M-CODE and Galileo PRS, with class-leading flexibility, coherence, fidelity, performance, accuracy, and reliability. PNT X functions as an integrated wavefront simulation system designed for the testing of CRPAs and other adaptive antennas. Highly configurable capabilities, including embedded spoofing and high-powered jamming across 16+ elements, provide the flexibility and control needed for demanding applications. Unrivalled precision and phase alignment make this the established choice for CRPA integrators. Building on the groundbreaking capabilities of the GSS9000 platform, PNT X introduces intuitive CRPA configuration, enhanced realism for non-standard signals, continuous dynamic range, and more, combining unrivalled features with uncompromising performance.
• Zoned chamber support: Atom test and measurement engineers have significant experience in configuring our patented zoned chamber environment for realistic OTA testing of adaptive antennas. We can advise and support on any aspect of setting up and configuring a zoned chamber.
• In-field testing: The Atom Portable Simulator enables the introduction of interference threats to authorized range testing. From over-the-air interference to GNSS-synchronized spoofing testing, the Portable Simulator adds another dimension to CRPA testing.

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Case study: DLR tests its GNSS anti-jam and anti-spoof technology with Atom

Discover how DLR used Atom GNSS Simulation technology to characterize the performance of its GALANT anti-jam and anti-spoof receiver, incorporating CRPA technology.

Read the case study

Why are adaptive antennas needed?

The need for sophisticated adaptive antennas is being driven by two macro forces. One is the increasing reliance of the world as a whole on GNSS technology. Satellite-based positioning, navigation and timing (PNT) now play an essential role in many areas of critical national infrastructure, from cellular networks and energy grids to aviation, shipping and rail transport.

At the same time, manmade threats to GNSS signals are increasing in prevalence, adding to existing natural threats like ionospheric scintillation, obscuration and multipath effects.

GNSS signal jamming is now extremely common, whether it’s short-range jamming from personal privacy devices (PPDs) used to block GPS tracking of company vehicles, or powerful jamming used by nation states to disrupt enemy operations in conflict zones, which can affect civilian receivers over a very wide geographical range.

In 2019, for example, the aviation organisation EUROCONTROL received an unprecedented 3,500 reports from pilots of GPS outages in the Eastern Mediterranean region, attributed to the various conflicts taking place in Syria, Libya and Azerbaijan.

GNSS spoofing (illicit broadcasting of fake or delayed GNSS signals) is on the rise, too – often occurring in targeted hotspots and affecting all unprotected receivers in the area. In 2019, for instance, mysterious ‘circle spoofing’ attacks occurred in parts of Shanghai and Tehran, causing ships and fitness trackers to appear to be moving in a circle.

How adaptive antennas work

It’s clear that safety-critical and liability-critical GNSS receivers need to be protected against such threats – and one proven approach is the use of adaptive antenna systems.

These systems come in various forms and varying degrees of sophistication, but the basic principle is that they work to reject interfering signals. This can be done either by physically blocking them (using a choke ring, for example) or by detecting the presence of interference signals and adjusting the antenna’s reception pattern to minimise or eliminate their impact.

The latter type, called a Controlled Reception (or Radiation) Pattern Antenna (CRPA), comprises multiple antenna elements that can be controlled individually. Algorithms detect interference signals and direct antenna elements to form a null in the direction of the interference source (known as null steering), or to direct gain towards genuine signals (known as beamforming).

There are many ways to design a CRPA. Some highly sophisticated and classified designs exist in the military domain, which provide very effective protection against jamming in high-interference environments. In our recent webinar, Andriy Konovaltsev of the German Institute of Communications and Navigation (DLR) presented the design of DLR’s prototype GALANT receiver, which uses an adaptive four-element antenna with beamforming algorithms.

The challenges of testing adaptive CRPA antenna systems

As adaptive antennas are mission-critical, thorough testing is essential, but it can present many challenges. GNSS receivers with adaptive antennas are complex systems, and designing a test regimen requires a system-of-systems approach to ensure that every element is tested both in isolation and as a whole functioning system.

Evaluating the performance of the physical antenna is particularly challenging, because it requires GNSS, interference and (if required) spoofing signals all to be transmitted over the air.

That can be done on an outdoor test range, but obtaining permits to generate over-the-air interference or spoofing signals can be difficult and time-consuming, and the logistics of getting all of the necessary equipment to the test range can be quite daunting.

There are also the other perennial drawbacks of real-world testing: the signal environment is not repeatable, many of its elements are not controllable, the environment is limited to the satellites in view at the test location, and so on.

 

The operation of a CRPA Antenna relies on adaptive signal processing techniques, including:

• Beamforming: The antenna array combines signals from multiple elements to create a directional reception pattern that enhances the gain toward legitimate GPS satellites.
• Null Steering: The system identifies the direction of interfering signals (e.g., jammers) and creates “nulls” in the reception pattern to minimize their impact.
• Spatial Filtering: By exploiting the spatial separation between desired and undesired signals, the CRPA can differentiate between legitimate satellite signals and malicious transmissions.