Efficient Computation of the Near-Field Mutual Coupling Between Antennas on Vehicles

Abstract: A near-eld generalization of Friis transmission equation has previously been proposed in the literature. Using this generalization, it is possible to calculatethe mutual coupling between two antennas as a weighted integral over the antenna far-fields. In this thesis, a change of variables is used to remove the singularity in the integrand and a normalization of the antenna far-field is suggested to take mismatch and thermal losses into account. The resulting non-singular integral has been implemented in a computer program that can be used to calculate the mutual coupling between two arbitrarily polarized antennas given the antenna far-fields and the geometrical separation between the antennas. The program has several advantages compared to previous programs based on the near-field generalization of Friis transmission equation. Firstly, this program can calculate the mutual coupling between two arbitrarily polarized and oriented antennas whereas previous programs could only be used for linearly polarized and polarization-matched antennas. Secondly, the advantage of the non-singular form is the improved numerical stability. The mutual coupling calculated using this program is demonstrated to agree well with results from full three-dimensional simulations of antennas located in each others near-fields using commercial software. Finally, we investigate for the first time if this integral relation can be used to calculate approximate values of the mutual coupling between antennas on an electrically large vehicle.