POWER TRANSFER BETWEEN ANTENNAS IN CLOSE PROXIMITY.

The article discusses the theoretical determination of the power transfer between aperture antennas so closely coupled that one is located in the Fresnel region of the other. A new approach to calculating the fields in the Fresnel region is included. A series expansion for the power transfer between aperture antennas is derived. The Friis formula is given for the far-field power transfer. For the near-field or Fresnel region, a new gain factor is determined and substituted in the Friis formula in place of the far-field gain. A more fundamental approach uses a general integral representation for the power transfer, but the expressions can be integrated easily only when the antenna separation is such that the far-field approximation applies. To avoid these complicated integrals, a novel approach is described using a plane wave and a number of plane wave derivatives. An expression for the generalized transmission coefficient is derived. However, application to rectangular apertures shows that the formula is inadequate for close spacings of apertures, since it is written in terms of an infinite series which apparently diverges when antenna separation becomes small. Author