Interference Localization using a Controlled Radiation Pattern Antenna (CRPA)

The need to ensure the continuous availability of Global Navigation Satellite Systems (GNSS) continues to increase along with the implementation of PBN and ADS-B. For this purpose, a Radio Frequency Interference (RFI) Mitigation Plan is being developed by Eurocontrol, which includes a comprehensive set of preventive and reactive measures to limit vulnerability to RF interference. Among the reactive measures is the need to be able to detect, locate and eliminate an RFI source in a timely and efficient manner. A cooperative concept is foreseen for this purpose, where aerial capabilities aim to quickly identify the approximate location of an RFI source. This should allow dispatching ground measurement vehicles to a limited search area, ensuring a good chance that the precise location of the source can be identified and lead to successful enforcement action. Limiting the time of exposure to an RFI source will then make an important contribution to mitigating GNSS vulnerability to RFI. However, currently, only very few flight inspection or other aerial work platforms are equipped with RFI localization capabilities with the sensitivity required to detect GNSS interference sources. Another problem is that if an aircraft flies into an area of GNSS interference, its own positioning capability may be impacted, affecting both aircraft navigation and the ability to fix the position of RFI sources. In order to both maintain ownship position while looking for RFI sources and improve the speed and accuracy of RFI source localization capabilities, the use of a GNSS CRPA is being evaluated. A CRPA is a Controlled Radiation Pattern Antenna, which can dynamically modify the gain pattern and either form beams of positive gain towards the satellite signals being received, or steer nulls (negative gain) towards the interference sources. The CRPA is expected to both preserve GNSS positioning while also providing at least an azimuth angle towards the source of the interference. If the latter is integrated with an AHRS (Attitude and Heading Reference System), only a few lines of position pointing towards the RFI source could provide a fast indication of the probable ground location. The paper will present the results of the conducted technical studies and test campaigns. Concept validation so far mainly includes laboratory simulations using a wavefront simulator, and open air tests using a moving van platform. An overflight with a flight inspection aircraft using a non-GNSS specific localization capability was conducted as well. The paper will discuss system integration challenges, operational concepts and provide results in terms of system sensitivity to typical RFI sources and angular accuracy.