English: Diagram of the electric field (E) around a quarter-wave monopole antenna (A), showing origin of end effect. "End effect" is the reduction in resonant length of an antenna due to storage of charge at the end. The drawing shows an antenna driven at resonance by a radio frequency oscillating voltage from a transmitter (S). Because the electric field at the top of the antenna rod spreads out in a fan ("fringing field"), the end part of the antenna has more capacitance and is able to store more electric charge per unit length than the rest of the antenna. As a result, the electric current distribution (I(z), red line) along the antenna departs from a sine wave (blue line) near the top; it decreases faster with height. As a result, the height of the antenna (h) at resonance is shorter than a quarter wavelength (λ/4). Another way to say this is the node of the standing wave (N) occurs not at the top of the antenna but some distance above it. The thicker the antenna rod, the greater the capacitance and the shorter the resonant length. For a typical quarter wave monopole, the reduction in resonant length is roughly 5%.