Extentions to the Theory and Design of Electric Wave-Filters

O N l i important problem which frequently arises in wave-lilter design is that of obtaining a terminal wave-filter impedance which is approximately a constant resistance at all frequencies in the transmitting bands. This ideal impedance characteristic is desirable where a wave-filter is terminated by such a constant resistance, as is usually the case. Under these ideal conditions, for frequencies in the transmitting bands all terminal reflection losses are avoided, and there are no impedance irregularities at the terminal junction to be reflected back through the wave-filter and produce objectionable impedance irregularities at the other end. The design of ladder type wave-lilters of any class,1 regarded from either the theoretical or the practical standpoint, involves taking into consideration two standard image impedances; and the internal or main part of a composite wave-filter structure, called the mid-part, usually has the equivalent of one or the other of these image impedances at each terminal. These two standard image impedances are the image ' " T h e o r y and Design of Uniform and Composite Electric Wave-Kilters," U. J. Zobel, B. S. T. J., January, 192.*. 28-1