Abstract: The Coupled Taper Slot line Antenna (CTSA) possesses the advantages of equa lized beam in both E and H planes, and reduced side lobes in H plane. With proper feed network, CTSA can radiate linear polarized sum and difference beams respectively. Although several methods have been employed to analyze a single TSA, it is lacking in theoretical analysis. In this article, radiation patterns are analyzed from a reaction integral equation by using MoM for a CTSA without dielectric substrate, the computational results are presented and discussed.