Cumulative coupling in antenna arrays

This paper describes a cumulative coupling problem encountered in large, uniformly spaced, flat, phased arrays. Large impedance mismatch and radiation pattern degradation can occur at certain critical scan angles for which the radar steering phase advances match the antenna coupling delays. Many antenna elements may then contribute in-phase, to the active impedance mismatch of an antenna element in the interior of a large array. Several phased arrays have exhibited scanning "blind" regions which appear to be a consequence of this phenomena. The mechanism is described here and equations are given relating the critical scan angle to antenna coupling coefficients.