The utilization of substrate integrated waveguide (SIW) higher-order modes can significantly reduce the number of metal posts and thus simplify the component structure. In this paper, two wideband excitation structures for higher-order modes in SIWs are proposed and investigated to implement slot arrays. Two parallel coupling slots along the SIW are used to excite the TE40 mode. The excitation structures exhibit broad bandwidth and good mode purity. Moreover, they can be extended to realize transitions exciting TE60, TE80, . . ., TEm0[m = 6, 8, . . . 2 x (n + 3), n is a natural number] modes. As application examples, a 4 x 4-element slot array is designed. Measured results demonstrate that the slot array inherits the merits of the excitation and shows a simple structure, broadside radiation, high aperture efficiency, and good radiation efficiency.