Abstract
This chapter gives an overview of the microwave diplexer, starting with a background into the radio frequency and the microwave spectrums. The chapter also covers the aims and objectives of the book, the motivation, and the diplexer design method discussed in the book. A detailed literature review into the various diplexer design and implementation approaches is also detailed in this chapter. The chapter also looks at a number of transmission line technologies that have been utilised in the implementation of microwave diplexers including slotline, stripline, coplanar waveguide, microstrip, waveguide, and the substrate integrated waveguide (SIW). The microstrip and the SIW implementations of the diplexer is reviewed in more detail, with numerous existing research examples. The chapter concludes by highlighting the emerging research and the opportunities in diplexer design introduced and established in the book.