Design procedure for multioctave combline-filter multiplexers

A new general design procedure is presented for multioctave multiplexers having any number of combline channel filters satisfying an equiripple response, with an arbitrary number of resonators, bandwidths, and interchannel spacings. The design procedure is developed for bandpass combline filters connected in series at a common junction for broadband applications. Commencing with the expression for element values of a double-terminated-bandpass prototype combline filter satisfying an equiripple response, the multiplexer design procedure modifies the elements in the nearer half to the common junction of each channel filter and preserves a match at the two points of perfect transmission closest to the band edges of each channel filter, while taking into account the frequency dependence across each channel. Examples of several multiplexers are given indicating that the design process is valid for a wide variety of specifications and gives very good results as demonstrated by the computer analysis of multiplex multiplexer examples and by the experimental example of a combline-filter diplexer constructed in a coaxial form of realisation.