Lower Bound on Scattered Power from Antennas

A lower bound on the total power scattered from a lossless and matched receiving antenna, for a given incident wave, is presented. The vector spherical wave expansion is used to describe the scattering and power absorption mechanisms. Scattering is the main reason behind antenna absorption. This poses a fundamental limit on minimization of antenna scattering. In other words, if we are to extract any power from the incident wave, the receiving antenna cannot be completely invisible, and scattering is an inevitable consequence of the power capturing process. To demonstrate the phenomena, a linear array antenna is optimized such that its scattered power is increasingly reduced and the total amount of scattered power for various incident angles is compared to our predicted lower bound.