The engineers at Narda Safety Test Solutions (STS) have developed an automatic direction-finding antenna for signals between 200 MHz and 2.7 GHz. Used with the SignalShark real-time receiver, the ADFA 1 quickly identifies a bearing - a complete measurement cycle takes just 1.2 ms - and is insensitive to reflections, ever present in urban environments. The antenna is compact, weighing just 5.6 kg with a diameter of 480 mm, making it well-suited for cellular network providers and security applications.
Direction finding measures the phase differences of a signal among several antenna elements. The heart of the ADFA 1 is an array of nine antenna elements around a central omnidirectional reference antenna. Combining the array with phase shifters and complex algorithms enables the ADFA 1 to precisely determine signal direction using only a single-channel receiver, at a much lower cost than multi-channel direction-finding systems. The central reference antenna receives signals from all directions, observing the broadband spectrum simultaneously with determining the direction of the signal being traced. The ADFA 1 also determines the elevation angle of the signal, which is important in urban settings where localizing to an individual floor may be needed.
In most applications, the ADFA 1 is attached to the roof of a vehicle with a magnetic mount, which does not require drilling holes or other modifications to the vehicle. The immunity of antenna performance to the mounting surface means that correction tables for the specific vehicle are not needed. Once the vehicle-mounted system identifies the building, an additional hand-held antenna can be used with the SignalShark to determine the floor and room where the source is located.