Input impedance of small antenna provides Purcell factor

The Purcell effect, which consists in change of a spontaneous decay rate, is a fundamental effect in a quantum electrodynamics of a quantum source- resonator interaction. However, a spontaneous decay effect is not a purely quantum phenomenon and is well known in classical physics. In this article the expression for the Purcell factor calculation through imaginary part of the Green´s function in relation to small dipole antenna is obtained. Developing this concept, we propose a new methodology of calculation and measurement of an electric and magnetic Purcell factor through an input impedance. The results of experimental verification of the proposed method in a microwave range are presented.