What does reciprocity theory suggest about antennas?

Reciprocity theory posits that the characteristics of antennas are the same when they are used for both transmitting and receiving electromagnetic (EM) energy. This principle is based on the fundamental physics governing electromagnetic fields and wave propagation. Essentially, an antenna that is designed to efficiently transmit signals at a certain frequency will also be equally capable of receiving signals at that frequency, given that it behaves symmetrically with respect to time-reversal operations.

This implies that the efficiency, impedance, and radiation patterns of antennas remain consistent whether they are transmitting or receiving, facilitating their dual functionality in communication systems. This symmetry is a vital consideration in antenna design and application, making them versatile components in wireless systems.