Everything in the universe vibrates or oscillates and emits energy. Because of the nature of matter itself, everything has two fields, an electrical field and a magnetic field, and these fields are emitted perpendicular to each other. Radiation is the propagation, or movement, of these two fields in a direction perpendicular to both of them. Thus, this radiation is called electromagnetic radiation.

Electromagnetic radiation is propagated in the forms of waves. Each wave has a crest and a trough, and the distance between two crests is defined as the wave's wavelength. The wave's frequency is defined as the number of waves per second.

The electromagnetic spectrum is the complete range of possible forms of electromagnetic radiation ranging from radiation with a low frequency and long wavelength to radiation with high frequency and short wavelengths. The electromagnetic spectrum is normally divided into the following ranges:

• Radio waves
• Microwaves
• Infra-red
• Visible light
• Ultraviolet
• X-rays
• Gamma rays

RF engineers specialize in working with devices that emit radiation in radio waves portion of the spectrum, which are used primarily for communications. Radio waves are further divided into the following four types, based on their wavelength.

• Long wave - 1 to 2 kilometers (1,000 to 2,000 meters) in wavelength
• Medium wave - 100 meters in wavelength (used for AM radio transmissions)
• VHF (Very High Frequency) - approximately 2 meters in wavelength (used for FM radio, aircraft and taxis)
• UHF (Ultra High Frequency) - less than 1 meter in wavelength (used in television transmissions)