Definitions and terms
Small Antennas

Small antennas are called "electrically small antennas" or ESAs. This name implies that their physical size is much smaller than their wavelength.

According to Wheeler , an antenna is said to be electrically small (ESP) if its maximum dimension is less than the wavelength λ divided by 2π. This value is commonly referred to as the "radianlength" and corresponds to the radius of the so-called "radiansphere". It constitutes the...