  Nonreciprocity in space-time modulated photonic crystals has been
investigated in the context of nonreciprocal propagation and polarization.
Here, we investigate a reconfigurable nonreciprocal wave growth in space-time
modulated crystals. Imposing an adaptable progressive phase shift between
successive time-modulated cells results in blue and red shifts of the forward
and backward momentum band gaps around the typical 0.5 growth normalized
frequency. We applied this spatiotemporal scheme to engineering the dispersion
relation of a loaded transmission line$-$a 1D periodic structure$-$in the
microwave regime.
