In-Situ Calibration of Antenna Arrays Within Wireless Locating Systems

Antenna arrays are frequently used for localization of active communication transmitters or passively reflecting radar targets by evaluating signal phases at spatially distributed antennas. Unfortunately, the localization performance is degraded because of mutual coupling, unknown time delays, and imprecisely known antenna positions, especially if large arrays with spatially distributed antennas are used. Furthermore, these errors are altered until the array is steadily installed at its destination, which occurs because of position misalignment and cable phase instability. Hence, an in-situ array calibration is necessary to perform faultless phase measurements. For this purpose, this article proposes a novel calibration procedure for antenna arrays, correcting both the mutual coupling and positioning errors using an incoherently transmitting beacon. Because the in-situ calibration will be affected by multipath, measurements at random reference positions within the array's near field are used for calibration. In addition, the algorithm copes with randomly varying path losses because of unknown antenna polarizations and patterns. Calibration measurements are performed, providing physically reasonable results without using an anechoic environment. Furthermore, the calibration results are validated via indoor localization using three antenna arrays that were calibrated with the proposed algorithm.