On the Physical Aperture and the Power that Exits a Surface Enclosing a Receiving Antenna release_ugrst7tnhvh7hc6wk4qgozlc2a

Abstract

A straightforward application of the Poynting theorem over a closed surface around a receiving antenna shows that the net power exiting the closed surface is related to an illuminated area, which is arbitrarily specified. However, One such specification can be usedto define the physical area, as shown below. This definition pertains to both large and small antennas, and has a finite value for wire antennas as well. Correspondingly, the concept of the aperture efficiency can be generalized and not be restricted to aperture antennas only. It is then seen that aperture efficiency determines the fraction of the incident power which is absorbed in the load of a matched receiving antenna, the rest of the power being scattered. For example, when the aperture efficiency tends to unity and the antenna is perfectly matched, then all the received power within the physical aperture as defined above is converted into absorbed power; i.e., the antenna acts as a perfect absorber.
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