On methods to estimate bandwidth performance for array antennas with ground plane

Array antenna impedance bandwidth performance is a critical factor for antenna design, in particular for arrays in radar application and more recently for array antennas in communication systems. A priori methods to quantify bandwidth include stored energy-based estimates through the quality factor antenna Q, and sum-rule based estimates based on the antenna as a scattering object. A recently introduced, array figure of merit, uses a square window or walltype estimate on the return-loss to obtain bounds in terms of return-loss level, bandwidth, scan-range and unit-cell specific geometrical and material information, it is based on a fundamental physics result, linking bandwidth to essentially the thickness of the array. An alternative approach is based on the Bode-Fano theory, resulting in bandwidth measures in terms of one or several quality factors. Both methods apply both to single and multi-band array antennas. Here we present these methods and make a comparison between the two approaches.