Israel Aerospace Industries has launched a new airborne COMINT system which uses innovative Vector Sensing Antenna techniques to find emitters.
Launched in mid-February the EL/K-7065VU ComDart is the latest Communications Intelligence (COMINT) Electronic Support Measure (ESM) to grace the Israel Aerospace Industries (IAI) stable. Covering very/ultra high frequency wavebands of 30 megahertz/MHz to three gigahertz, the EL/K-7065VU is intended for space-constrained platforms like Uninhabited Aerial Vehicles (UAVs). IAI says that ComDart uses an innovative approach to locate emitters of interest in the form of a Vector Sensing Antenna (VSA).
TDOA and AOA
Traditionally, many ESMs use techniques like Angle of Arrival (AOA) and Time Difference of Arrival (TDOA) to find emitters. AOA will use two or more antennas which may be mounted on an aircraft’s fuselage or wings, on a ship’s mast or on a vehicle connected to an ESM. Each antenna will be capable of determining the bearing of an incoming signal. For instance, the emitter may be to the northeast of antenna A but to the northwest of antenna B. The point at which these two bearings cross, using the principle of triangulation, is where the emitter is located.
Likewise TDOA exploits an elegantly simple principle: Radio waves travel at 161,595 knots-per-second (299,274 kilometres-per-second). Let us suppose that an emitter is located 30 nautical miles/nm (16.2km) from antenna A but 20nm (10.8km) from antenna B. The signals from an emitter will take 0.0541 milliseconds/ms to reach antenna A, and 0.036ms to reach antenna B. Now imagine that you have drawn one ring around antenna A with a radius scaled to represent 30nm and one around antenna B with a scaled radius of 20nm. The point at which these two circles meet will be where the emitter is located. It does not matter how far or close the two antennas are from one another. As long as they are not located at exactly the same location, there will always be a difference in the time it takes the same signal to reach the antennas, albeit very small if they are very close together.
Both these techniques are reliable ways of determining where an emitter is, but in the air context, it can require two or more antennas to be placed on the airframe. The more antennas are used, the more reliable the determination of the emitter’s location. Using several antennas can be challenging if the ESM must outfit a diminutive airframe like a small uninhabited aerial vehicle. Where it is not possible to fit the multiple antennas on a single airframe to exploit TDOA/AOA techniques, “simultaneous detections from separate platforms are necessary to triangulate these angles and provide the location of the emitter on the map,” said IAI in a written statement provided to Armada: “Often, in practice, only a single platform is available, and legacy systems would need to move in space and rely on multiple communications from the emitter to provide a location. This is often difficult or impracticable to achieve.”
Vector Sensing Antenna
IAI has taken a different approach with ComDart using a Vector Sensor Antenna (VSA). According to IAI’s written statement the VSA uses a digital terrain map of the territory underneath and around the aircraft carrying the ESM. Meanwhile, the ESM will detect the bearing of the emitter of interest relative to the aircraft: “By calculating the point of intersection between this vector and a digital map of the terrain, an accurate two-dimensional geolocation is achieved,” says the company. One advantage of VSA architecture is that the “small size of the VSA as compared to TDOA or AOA antenna arrays, allows for installation on smaller platforms that cannot accommodate legacy technologies.” The antenna is circa 200mm by 300mm in size.
IAI is moving ahead with bringing the product to market: “We have finished development, and we are ready for full flight demonstrations.“