A transmission grating can be used as a frequency scanned antenna, provided most of the incident power is transferred to the diffracted mode, i.e., the grating is blazed. A design procedure for blazing a rectangular bar transmission grating is presented. The performance of a number of gratings is presented. Efficiencies in excess of 99% can be obtained at a single frequency. A scan range of 55° between 3-dB points can be obtained.