Nonreciprocal signal growth in space-time modulated transmission lines

Nonreciprocity in space-time modulated photonic crystals has been explored in the context of nonreciprocal propagation and polarization. In this study, we investigate reconfigurable nonreciprocal wave growth in space-time modulated crystals. By imposing an adaptable progressive phase shift between successive time-modulated cells, we induce blue and red shifts in the forward and backward momentum band gaps around the typical normalized growth frequency of 0.5. This spatiotemporal scheme is applied to engineer the dispersion relation of a loaded transmission line-a 1D periodic structure-in the microwave regime. The nonreciprocal wave growth is studied and analyzed under conditions that either allow or forbid backward propagation.