1. Definitions and terms

1.1 Electrically small antenna

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 boundary between the near field, where electromagnetic energy is stored in the antenna, and the...