Limitations of online calibration methods in antenna arrays

Various online calibration methods have appeared in the scientific literature for attempting to correct errors in antenna arrays using signals of opportunity. These methods are also known as autocalibration, self-calibration and blind calibration methods, and have the principal advantages of not requiring calibration sources in known locations and to adapt seamlessly to a changing electromagnetic environment. The studies concerning online calibration methods have only considered very favorable scenarios, and it is currently unclear how they would perform in realistic conditions. In this paper, important underlying assumptions in online calibration methods are highlighted to understand their limitations, and three methods used with uniform linear or circular antenna arrays are evaluated.