We derive explicit design rules of optical phased-array planar 1 × N switch to achieve small insertion loss, large extinction ratio, and non-dispersive waveguide structure required for wavelength-independent broadband operation. The minimum number of phase shifters and slab lengths were studied as a function of N and the optimized array shape was derived to minimize the optical path length. We show that the length depends nonlinearly on N, and may become significantly shorter compared with that of a tree-structured switch under certain conditions.