We propose the silicon-on-insulator (SOI) based, phase shifted vertical side wall grating as a resonant transmission filter suitable for dense wavelength division multiplexing (DWDM) communication channels with $100\mathrm{GHz}$ channel spacing. The gratings are designed and numerically simulated to obtain a minimum loss in the resonant cavity by adjusting the grating parameters so that a high transmittivity can be achieved for the resonant transmission. The resonant grating, which is designed to operate in the DWDM International Telecommunication Union (ITU) grid C band of optical communication, has a high free spectral range of $51.7\mathrm{nm}$ and a narrow band resonant transmission. The wavelength selectivity of the filter is improved through a coupled cavity configuration by applying two phase shifts to the gratings. The observed channel band width and channel isolation of the resonant transmission filter are good and in agreement with the ITU specifications.