Anti-jam antennas protect against GNSS interference by dynamically adjusting the effective antenna gain pattern and steering 'nulls' in the gain pattern towards the direction of the interferer. This prevents the majority of the interfering power from entering the GNSS receiver. NovAtel's GPS anti-jam technology uses multiple antenna elements and digital null forming antenna electronics, allowing a connected receiver to continue to provide a PNT solution in the presence of interference.
Multi-frequency receivers also provide a means of protecting against interference. For example, if interference in the L1 frequency band around 1575 MHz is completely jamming GPS and GLONASS, it is usually possible to continue to calculate a PNT solution using the L2 GPS and GLONASS frequency band around 1227 MHz.
If the duration of the interference is short, an integrated solution, like NovAtel's SPAN® technology, which deeply couples a GNSS receiver with an Inertial Measurement Unit (IMU), can be used to bridge the GNSS outages. In general, the better the quality of the IMU, the better the PNT solution during these outages. Additional sensor inputs such as odometer or altimeter inputs can be used to further aid the PNT solution, and there is a growing trend to use low-frequency RF systems like eLoran in conjunction with GNSS and other sensors.
With any GPS denied scenario, it is ideal to have situational awareness to know if jamming (intentional or otherwise) is occurring so that actions can be taken to reduce or eliminate the jamming. NovAtel® has been conducting research in this area by taking samples of the GNSS Radio Frequency (RF) spectrum and time-tagging the samples with precise GNSS time stamps. This is done with standard NovAtel OEM628™ receiver hardware. Neil Gerein, NovAtel's Defense Product Manager stated, “By analyzing short “snapshot” samples, we can not only detect jammers, but also “fingerprint” the jammer by examining the signal characteristics. Taking this one step further we have demonstrated that if multiple receivers can 'see' the jammer simultaneously we can determine the location of the interference source.”
In March 2014 the Canadian Army conducted trials of NovAtel's GPS Anti-Jam Technology(GAJT®) in an operational environment. The successful trials, which were done under the auspices of the Build in Canada Innovation Program (BCIP), showed that GAJT protected the Position, Navigation & Timing (PNT) systems of the vehicle even while there was GPS jamming in action. The Light Armoured VehicleIII Observation Post Variant (LAV III OPV) was chosen for its particular PNT needs, especially for artillery target acquisition equipment which was shown to operate with GAJT to the same level of precision and functionality as with the standard GPS antenna.