A Group of Near-field Coupling Formulae for Closely Spaced Electrically Large Antennas by Modified Friis Equation and Power Balance Theory

This paper has theoretically presented a group of the near-field mutual coupling formulae for the closely spaced electrically large antennas (ELAs) when the normalized far-field distance no more than 0.125 by the modified Friis transmission equation (MFTE) and the uniform path-loss (UPL) model based on the power balance theory (PBT). Firstly, the near-field MFTE and the surface area of the Fresnel ellipsoid has been introduced. Secondly, the on-axis or off-axis coupling formula in the Fresnel region has been deduced, respectively. Finally, the effectiveness has been validated by comparing the near-field measurements with the numerical simulation. It shows that this paper suggested formulae are effective on ELAs near-field coupling forecast.