Analogies with physical phenomena indicate that modulation of a material or geometrical parameter of a periodic structure enriches its original band structure. The present work aims to provide an insight into the band-splitting phenomenon in the case of commensurate modulation for a parallel-plate waveguide technology-based geometry. A modulated one-dimensional parallel-plate waveguide signal integrity structure is numerically analysed to exhibit the appearance of band splitting and new bandgaps. The modulation mechanism has a potential in dispersion engineering, as it allows controlling the number and position of the electromagnetic bandgaps and the in-band characteristics of the field propagation. Generation of modes with negative group velocities for a given frequency band is also achievable by this technique.