Negative group velocity and anomalous transmission in a one-dimensionally periodic waveguide

This study presents a theoretical investigation of the negative group velocity (NGV) and anomalous transmittance of waves in the stop band of a corrugated parallel-plate waveguide (CPPWG). The two different schemes, scattering analysis for a finite CPPWG and the dispersion relation of an infinite CPPWG, were used to investigate the physical insight of the wave process. The NGV zone corresponds to the stopband slanted at an angle on the Brillouin diagram, following the mutual verification of the results obtained by the two different approaches. This class of stopband is caused by the contra-flow interaction between the fundamental mode and the space harmonics of higher-order modes. Additionally, fluctuation was also found in the transmitted coefficient within the conventional stopband, caused by the excitation of the first higher-order mode within the stopband of the fundamental mode.