Grating-Lobe Suppression for Periodic Leaky-Wave Antennas at the Full Array Level

The scanning range of a periodic leaky-wave antenna (P-LWA) is limited by the appearance of grating lobes, which are brought by the radiation of higher order space harmonics. The proposed method in this letter manipulates the phases of space harmonics and suppresses the grating lobes at the full array level. The P-LWAs operate as subarrays with their perturbations successively shifted along the propagation direction. Feeding the P-LWAs with specific phases, the radiation of the desired space harmonic is retained while radiation of other space harmonics is cancelled out. The proposed method is capable of achieving a large scanning range with a relatively small waveguide index (defined as ${n}_g = {{{\lambda }_0} \mathord{/ {\vphantom {{{\lambda }_0} {{\lambda }_g}}} } {{\lambda }_g}}$). Specifically, the single-beam full-space scanning can be realized with ${n}_g$ less than 2, which is the lower limit for existing works. Based on the proposed method, A prototype consisting of three subarrays was designed with ${n}_g \!=\! 1.426.$ A main lobe pointing to $41.1^\circ $ was realized with two grating lobes suppressed by more than 11 dB at $ - 6.5^\circ $ and$ - 61.8^\circ $. The sidelobes brought by the slow-wave radiation were also obviously suppressed. Measured results agree well with the simulation and the theoretical prediction.