Microwave Filters for Communication Systems: Fundamentals, Design and Applications

CHAPTER 18

MULTIPLEXER THEORY AND DESIGN

Previous chapters have dealt with the design of microwave filters as an individual component of a communication network. In a multiuser environment, communication systems employ a range of microwave filters as individual components, as well as part of a multiport network required to separate or combine a number of RF channels. This is commonly referred to as a multiplexing network or simply a multiplexer. This chapter is devoted to the design and tradeoffs of multiplexers for a variety of practical applications.

18.1 BACKGROUND

Multiplexers (MUXs) are used in communication system applications, where there is a need to separate a wideband signal into a number of narrowband signals (RF channels). Channelization of the allocated frequency band allows flexibility for the flow of communication traffic in a multiuser environment. Amplification of individual channels also eases the requirements on the high-power amplifiers (HPAs), enabling them to operate at relatively high efficiency with an acceptable degree of nonlinearity. Multiplexers are also employed to provide the opposite function, that is, to combine several narrowband channels into a single wideband composite signal for transmission via a common antenna. Multiplexers are, therefore, referred to as channelizers or combiners. Due to the reciprocity of filter networks, a MUX can also be configured to separate the transmit and receive frequency bands in a common device, referred to as a ...