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.
TopBackground
The need for miniaturisation, as well as reduction of design complexity, of microwave and millimetre-wave components, circuits and devices; while maintaining (or even improving on) the RF/Microwave performance of such components, circuits and devices has recently drawn a lot of attention from researchers in the RF world. The term microwave, in this context, is used to describe electromagnetic (EM) waves with frequencies beginning from 300 MHz and ending at 300GHz. The microwave frequency range (i.e. 300 MHz to 300 GHz) corresponds to the free space wavelengths of 1 m to 1 mm as shown in Figure 1. EM waves with frequencies ranging from 30 GHz to 300 GHz are now commonly known as the millimetre-waves because their wavelengths fall above 1 millimeter and below 1 cm, i.e. ranging from 1 mm to 10 mm. Radio frequency (RF) spectrum lies below the microwave frequency spectrum. The boundary between RF and microwave frequencies is arbitrary and depends on the particular technology developed for the exploitation of the given specific frequency range (Hong & Lancaster, 2001). It is important to note that the frequency values in Figure 1 is inversely proportional to the wavelength values as prescribed by Eqn. (1) where c0 is the speed of light in free space, f is the frequency, and λ is the wavelength.
Figure 1. Radio frequency and microwave spectrums