On the Impact of the Mutual Reactance on the Radiated Power and on the Achievable Rates

In this brief, we consider the mutual reactance of hypothetical isotropic radiators and the influence of the mutual reactance on antenna arrays with zero mutual resistance. We compute the mutual reactance of hypothetical isotropic radiators using passivity, which has not been considered in wireless communications literature. We show that when an antenna array with zero mutual resistance is excited by ideal current sources, the mutual reactance does not have any influence on the radiated power. However, practical radio frequency amplifiers are not ideal current sources, but can often be modeled as linear sources. Then the radiated power depends on the mutual reactance. Furthermore in receive mode, the mutual reactance introduces noise correlations between the antennas. Numerical results show the impact of neglecting the mutual reactance on the radiated power and on the ergodic up- and downlink rates in an independent and identically distributed channel for a base station using a uniform linear array consisting of hypothetical isotropic radiators spaced by λ/2, or a uniform circular array consisting of 3 λ/2-dipoles.