Near-Field Analysis of Electromagnetic Interactions in Antenna Arrays Through Equivalent Dipole Models

This paper presents an analysis of the near fields of antenna arrays using an alternative approach taking into account field variations due to mutual coupling. The method does not require solving Maxwell's equations under the customary boundary condition, but is based instead on searching for equivalent dipole models that are capable of reproducing the same radiated fields of the actual array (ideally obtained through accurate measurement.) We treat mutual coupling between array elements as essentially a multiple scattering effect and propose a method to calculate the near field of arbitrary linear arrays with significant electromagnetic coupling. It is found that a single (analytical) dipole model obtained under certain circumstances, which are detailed in the paper, can be used to predict correctly the near field radiated by arbitrary-size antenna arrays. The paper ends by developing an application of the equivalent dipole method by expanding the near fields into a sum of propagating and nonpropagating parts. It is shown that the 3-D spatial Fourier transform required in this expansion can be eliminated when the dipole model is used in computing the near field in the domain of the validity of the model.