Broadside Radiation From Chern Photonic Topological Insulators

Broadside radiation from Chern photonic topological insulators (PTIs) is studied in this work. The one-way dispersion of the topological edge mode is located in the fast wave region, making leaky-wave radiation possible. In this communication, design guidelines are presented and validated by full-wave simulations: the Berry curvature and the Chern number of photonic crystals are calculated to design a topological edge mode, then a leaky-wave antenna is proposed where a perturbation is utilized around the source location to eliminate open-stopband behavior and generate broadside radiation with high efficiency. It is demonstrated that leakage of the topological edge mode is capable of both frequency and bias scanning to generate a steerable beam across the broadside direction. Moreover, the mechanism behind the immunity of PTIs to defects is also investigated in detail. Although topological edge waves can bypass PEC-slab defects ideally, the phase change along the defect affects the radiation pattern. The switch between sum-difference beams by tuning the scale of the PEC-slab is direct evidence to verify our analysis. To sum up, the open-stopband behavior is overcome to realize broadside radiation, and the conditional robustness of PTIs in terms of antennas is clarified.