Equivalent circuit for aperture antennas

The commonly used equivalent circuit based on a constant voltage generator does not correctly characterise scattering by an aperture antenna, nor does its dual, the constant current generator. This long-standing dilemma has been resolved by combining voltage and current sources to form a constant-power source. The power generated by this source is equated to the available power in a plane wave incident on the aperture. The voltage and current of the two sources and their respective internal impedances are then completely determined from a knowledge of the aperture area A0, the impedance ZA, the aperture efficiency ¿0 and the relative power pattern p(¿, ¿) of the antenna.