This lecture lists the frequency ranges over which radio frequency waves (RF), microwaves and millimetre waves are commonly defined.

RF is typically defined across the range 30kHz to 3GHz with 1GHz = 1,000,000,000Hz.

We then discuss the idea of lumped element and distributed circuits. Distributed circuits become increasingly important at higher frequencies because the physical size of conventional lumped element components (such as resistors, capacitors etc.) becomes comparable to the wavelength of the RF waves passing through them.

We also consider the importance of RF and the remarkable growth many applications now in widespread use throughout society.