The growth of the field of electric wave filters since their original discovery by Dr. G. A. Campbell shows the filtering action by no means inheres in any particular ph ysical configuration. Filters have been built, for example, as recurrent or non-recurrent ladder structures, as lattices, as bridged-T's, and in a variety of combinations of transformers with ordinary elements. No general theory uniting all these configurations has, however, been developed. Each structure has been treated by methods which are primarily adapted to that configuration alone. In consequence, such questions as the relations between filters of different types and the possibilities of securing improved characteristics by going to a still wider variety of configurations have remained unsettled.
El autor presenta una teoría general de los filtros eléctricos contemplados como estructuras eléctricas y desde un punto de vista físico-matemático. No hay que olvidar que el inventor del filtro eléctrico como circuito aplicable en comunicaciones electrónicas y sistemas de control fue G.A. Campbell que lo patentó en 1922.