Digital Waveguide Filters

A Digital Waveguide Filter (DWF) is any digital filter built by combining unit-length waveguide sections together [411]. In the case of a cascade (series) combination, they are essentially the same as microwave filters [346] and unit element filters [127]. This appendix, adapted from [411], shows how DWFs constructed as a reflectively terminated, cascade chain of waveguide sections can be transformed by means of elementary equivalence transformations to conventional ladder filters, such as those used in speech modeling [275].

Digital waveguide filters (DWF) are obtained (conceptually) by sampling the unidirectional traveling waves which occur in a system of ideal, lossless waveguides. Sampling is across time and space. Thus, variables in a DWF structure are equal exactly (at the sampling times and positions, to within numerical precision) to variables propagating in the physical medium in an interconnection of uniform transmission-lines.