Air defense

CRFS passive RF technology detects & geolocates commercial & military airborne emitters with a high degree of discrimination and accuracy 


Despite its versatility, radar emits RF energy, enabling counter targeting by hostile forces. Passive air defense systems can augment radar by identifying and geolocating aircraft transmissions while remaining invisible to electronic detection. RF receivers deployed at ground level, operating 24/7 can be tuned to detect specific signals of interest (ADS-B, TACAN, IFF, tactical data links) emitted by airborne targets.  

CRFS’ air defense solution allows users to hunt across a wide and congested spectrum with dedicated signal detectors that discriminate specific signals of interest hundreds of kilometers away from the RF sensor network.  

It uses wide-area 3D TDoA to achieve highly accurate geolocations of airborne targets over time. For longer ranges (hundreds of kilometers), the system uses directional antennas to provide a 2D geolocation line of bearing derived from time-of-flight data.  

Results can be displayed in any number of ways to represent distance, signal strength, signal type. Users can identify specific transmission types and fade geolocations over time to build a complete intelligence picture. This data can be displayed live or fed into an existing C2 system. 

  • Passive real-time situational awareness 

  • Commercial / military applications 

  • Intelligent detectors 

  • Discriminatoryaccurate geolocation 

  • Proven hardware & software 

  • Open architecture for third-party integration 

  • Highly configurable  

Air defense applications

Radar augmentation

Passive air defense can complement radar by detecting hostile airborne targets without alerting the enemy, providing covert intelligence and augmenting friendly missile defense systems.  

Spoofing detection

Passive air defense systems can detect spoofing by analyzing emission signatures, cross-verifying geolocations, and assessing signal behavior against established baselines and patterns of life. 

Detection of military & commercial drones

CRFS RF receivers provide wide frequency capability to detect MALE, COTS, and modified drones operating on frequency bands from 100 MHz to above 10 GHz. 

Target acquisition

By leveraging the capabilities of passive detection, militaries can maintain the element of surprise and improve the effectiveness of their defense and offensive strategies. 

Border security monitoring

Passive systems can detect and geolocate aircraft flying below radar coverage or attempting to evade detection by using terrain-following techniques.  

Talk to an advisor about air defense

Air defense expertise

Principles of geolocation techniques

This white paper describes the underlying principles of geolocation techniques (AoA, TDoA, FDoA, & PoA) and outlines their applications.

Passive geolocation with 3D TDoA
Learn about the passive technique known as Time Difference of Arrival (TDoA), which uses the time difference between receipt of signals at spatially separated receivers to determine the location of the source.
Advanced geolocation capabilities

Learn about advanced geolocation capabilities, AoA, TDoA, PoA, multi geolocation, and much more.


How a NATO partner built an air defense platform to increase national security 

Read the story

Related reading

Passive air defense: geolocating airborne targets using detector-based 3D TDoA
Passive air defense: geolocating airborne targets using detector-based 3D TDoA
by Jon Bradley
While radar is a widespread and versatile tool for detecting and locating in the battlespace, it has a critical Achilles heel. As active systems, radars have their own EMS ...
Radar Jammers and Where to Find Them
Radar Jammers and Where to Find Them
by CRFS Marketing
A fully functioning radar provides crucial situational awareness in a wide variety of military settings. And as a key component in the electronic warfare arsenal, it is likely to ...
Tracking Multiple Targets with 3D TDOA
Tracking Multiple Targets with 3D TDOA
by CRFS Marketing
In a recent blog post, we described how 3D TDOA could be used to detect spoofed ADS-B signals from aircraft. And it’s fair to say that the area around an airport is a heavily ...