Abstract: The distribution characteristics of electromagnetic field and surface current, which arise from the single ridge waveguide, are investigated by theoretical analysis and simulation, and then a novel slot array fed by single ridge waveguide is proposed for C band based on computer aided design. The array antenna is implemented by inserting slots in the ridge-walls of the single ridge waveguide. Therefore, the cross-polarization radiation of adjacent slots will be restrained for alternately tilted angles of slots. Simulation results show that the cross-polarization of array antenna is -50.26 dB, while the size is reduced by 53% compared to rectangular waveguide.