I. Introduction
A recent study of a phased array antenna for an airborne weather radar application [1] required evaluation of the array's integrated sidelobe ratio (ISLR), which is the ratio of energy in the sidelobes of the radiation pattern to that in the main lobe. ISLR is most commonly applied to the point-spread function of a synthetic aperture radar (SAR) image, but the customer for the weather radar study specified it for the antenna pattern itself. While textbooks and papers discuss the importance of ISLR and its impact on SAR system performance, a literature search performed for the study just mentioned turned up no references to ISLR computed for an antenna radiation pattern.