fonction de gain

OBS: Variation du gain d'une antenne de réception en fonction de la direction de réception.

CONT: In evaluating the performance of an antenna as a radiating system one considers only the field at a large distance, where the induction field can be neglected. The antenna is then treated as an effective point source, radiating power that, per unit solid angle, is a function of direction only. The directive properties of an antenna are most conveniently expressed in terms of the ""gain function"" ... The gain function is defined as the ratio of the power radiated in a given direction per unit solid angle to the average power radiated per unit solid angle ... The maximum value of the gain function is called the ""gain"" ... The gain of an antenna is the greatest factor by which the power transmitted in a given direction can be increased by using that antenna instead of an isotropic radiator.