In an ADFA, there are several elements of antenna arrays, an omnidirectional reference antenna, four phase shifters, a summing stage and a switch matrix. The ADFA translates signals from several antenna elements into a single-channel DF signal. The SignalShark controls and synchronizes the switch matrix and determines the bearings automatically, based on the single-channel DF signals. A complete bearing cycle can be as short as 1.2 ms for channel bandwidths greater than or equal to 3 MHz.
The DF method used in conjunction with the circular arrays is the correlative interferometer.
A bearing measurement or bearing cycle is a sequence of signal power measurements for each antenna element in combination with four phase shifters.
The parameter Cycle Time is the time needed for one complete bearing cycle. For the circular arrays it is the result of:
1 omnidirectional measurement
= 37 power measurements The filter settling time equals the minimum configurable measurement
time. In general: Broader CBWs allow shorter cycle times down to 1.2 ms. |
SignalShark calculates a so called covariance vectors out of this power measurements for every bearing cycle. This covariance vector is then correlated to stored reference data to evaluate the azimuth and elevation angle of the bearing.
The omnidirectional power and spectrum of the reference antenna element are also measured at the end of each bearing cycle, so the measurement results consists of bearings, as well as omnidirectional level and spectrum values This makes it possible to monitor changes in the signal level or spectrum concurrently with the bearings. Thus, you can optimize your bearing settings to the signal of interest and monitor the adjacent channels.
Following three conditions must be met to get a valid bearing:
1. The average power of the signal at the reference element is the same during all four power measurements for a single antenna element.
2. The signal to noise ratio is sufficiently high during the entire bearing measurement time.
3. The angle of arrival does not change during the entire bearing measurement time.