Introduction to Important Concepts of RF, Microwaves, and mm Waves Technologies

A commonly used term for higher-frequency spectrum includes radio frequency (RF), microwave, and millimeter wave. All these three bands together cover the frequency range from 1 MHz to 300 GHz. The corresponding wavelength range is from 300 m to 1 mm (Oliner, IEEE Trans Microw Theory Tech, MTT-32, 1022–1045, 1984; Sarkar et al., History of wireless, Wiley, Hoboken, 2006). The RF band is also referred to as meter waves as the corresponding wavelength is in meters; at microwave frequency, the band wavelength is in cm; thus, technically, it can be called cm waves, and finally, the wavelength is in millimeters in the mm-wave frequency band. These frequency bands have distinctive features, wherein low-frequency circuit theories cannot be applied as signals are represented as waves. Some of the unique characteristics of these high-frequency bands are discussed in this chapter. RF to mm-wave bands cover almost all wireless applications. The important applications of these frequency bands are also discussed here, including 1G–5G communication systems, which have evolved into indispensable constituents of our day-to-day life.