VHF / UHF Filters and Multicouplers: Application of Air Resonators

Chapter 7

Channel Multiplexing

7.1. Definitions

Having finished the individual study of filtering elements, it is now possible to tackle that of the association of filters or cavities. The generic term which covers this technique is that of multicoupling. We have seen previously that the word coupling entered the definition of different concepts: there was the coupling of resonators, entry/exit coupling, undercoupling, overcoupling, and there is now multicoupling, which is not a concept but a technique. It consists of making arrangements of several filters, in the most general meaning of the term, in order to realize in the first place a multiplexing of radio channels. The problem is always the same: on one side there is a single antenna and on the other several radio channels that must reach it, which means several emitters or receptors, or both at the same time. It is thus necessary to conceive equipment ad hoc, as passive as possible, and with minimal losses, that allows each channel to use the antenna as if the other channels did not exist. To do this it is necessary to dispose of two types of components: firstly, selective filters, cavities or band-pass, which attenuate the neighboring frequencies sufficiently, and afterwards a system of interconnection by means of lines, very often coaxial cables, that by transformation of the impedance will present, at a common central point, the other channels as open circuits. This will be the harness.

7.2. The duplexer

The simplest of ...