Abstract-Performance of a fully planar four-port crossover coupler is investigated. This bisymmetric circuit consists of a ring and two inner orthogonal sections connecting the diagonal ports. Based on the transmission line theory, analysis equations are formulated and design curves are presented. Two crossover junctions are fabricated and measured for validity confirmation. The measured data have good agreement with simulation.Index Terms-Crossover, directional coupler, four-port network, transmission line theory.