Adiabatic Floquet-Wave Solutions of Temporally Modulated Anisotropic Leaky-Wave Holograms

In this paper, the aperture field estimation technique and generalized adiabatic Floquet-wave expansion method is developed for two-dimensional temporally modulated anisotropic holograms. The determinant equations for propagation eigenstates in the presence of space-time modulation are obtained, and the behaviors of the corresponding dispersion curves are investigated. Injecting temporal modulation causes asymmetrical displacement of the dispersion curve, which is studied in detail in this paper. The consequence of temporal modulation is the Doppler-shift effect and nonreciprocal response observed in these structures. Results show that its nonreciprocity can be controlled by varying the modulation frequency injected to the hologram. The proposed method significantly expands the range of applications of leaky-wave holograms. The main advantage of leaky-type modulated metasurfaces over the transmissive/reflective counterparts is their non-protruding feeds making them suitable for integrated structures. As an example, a nonreciprocal circularly polarized hologram is designed. Tensorial impedance surface is exploited to achieve high polarization purity.