Ideal wave filters

The increasing usefulness of wave filters in the telephone plant, together with rising standards of quality, emphasizes the need of a systematic method for approximating ideal characteristics as closely as we please. By an ideal filter is meant a network having the properties of a distortionless transducer over a given frequency range and suppressing all other frequencies. A design method is presented whereby an arbitrarily close approximation to these properties may be realized in a physical network. Examples of actual designs illustrate the engineering features involved in the practical application of the theory.