Abstract— In this paper, filtering characteristics of guided waves in a rectangular waveguide with corrugations on the side walls are investigated. The parameters of the sidewalls offer an added degree of freedom to the filter designer for controlling the width of the stopband region. A rectangular waveguide with sinusoidal and square corrugations, that are uniform along the structure depth, is simulated using two commercial full-wave solvers, the HFSS and CST Studio Suite. However, the frequency response for a uniform waveguide with sinusoidal corrugation has the undesirable effect of high ripple levels, which corrupts the filter response without a clear isolation between stop-band and pass-bands. Apodization profile is introduced to decrease the level of the ripples. The Gaussian apodization profile has been examined. The square corrugation profile has been used to investigate the multi-bands in the frequency response.