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.