RF Direction Finder (DF) Arrays

What is Direction Finding?

Direction finding (DF) or Angle of Arrival (AoA) techniques are perhaps the most conceptually straightforward geolocation methods available. We simply measure the direction from which a signal arrives, and then project a line of bearing (LOB) back out along the same direction. Doing this with receivers at two spatially separated locations allows two LOBs to be drawn, which will intersect at the signal source position.

This conceptual simplicity at the surface level, though, obscures a more complicated picture. The devil is in the detail, and in this case, the detail is in the seemingly simple task of working out the direction of the incoming signal.

Radio Direction Finders – RFeye Array

RFeye Arrays are available in a range of sizes and antenna configurations for fixed or vehicle-based deployment. With frequency range options from 20 MHz to 18 GHz and twin receiver channels, Arrays provide simultaneous monitoring, DF and geolocation capabilities.

Superior signal interception

The RFeye Array is a fully integrated, multi-mission system for continuous 24/7 spectrum monitoring and surveillance. Used for detecting and locating unauthorized, suspicious or interfering transmitters, Arrays are designed to:

  • Intercept signals, however transient
  • Perform signals analysis and classification
  • Geolocate target transmitters

This can all be performed in real time or recorded for future analysis.

The RFeye Array uses a unique multi-layer approach that is more sophisticated and versatile than traditional RF antenna direction finding systems. High performance spiral directional antenna modules are optimized for different frequency bands and arranged in multiple orientations. The Array is sensitive to the majority of incoming signal polarizations, including all linear polarizations, allowing reliable detection of signals, including those invisible to most DF systems that use only vertically polarized direction-finding antennas.

Beyond direction finding

The RFeye receiver commutates at very high speed around the antennas to make near-simultaneous measurements in multiple directions. It measures correlations and calculates actual positional probabilities using augmented Time Difference of Arrival (TDOA) and/or Power on Arrival (POA) techniques. In addition, it gives an Angle of Arrival (AOA) bearing based on received power at each antenna.

Measurements from these different techniques can be overlaid onto a wide variety of maps, satellite images and 2D/3D GIS datasets to give a unique positional display showing source geolocation probabilities. All signal types can be mapped, irrespective of signal power, bandwidth or frequency.

RFeye Array 300 mounted at a satellite ground station

Modular and flexible deployments

Each RFeye Array is fully self contained within a robust IP65-rated radome designed for hostile conditions. Close coupling of the RFeye Node and antenna modules reduces cable runs and cable losses and significantly improves performance at higher frequencies. Various directional antenna options are available from 100 MHz to 18 GHz, and a frequency extender module is available for AOA on VHF signals down to 20 MHz. Arrays can be networked over large distances as part of a wider monitoring and TDOA network with other RFeye receivers.

CRFS Van with Array 300

Array 300 mounted on a van

Array 100

Vehicle-mounted, transportable or ground-fixed installations

Array 300

Outdoor ground-fixed or vehicle-mounted installation complete with IP65-rated radome