Efficient Methods to Calculate Mutual Coupling between Generic Antennas on Large Platforms

Sammanfattning: This thesis presents research on methods for calculating the mutual coupling between antennas. The mutual coupling between antennas is a measure of the amount of energy transmitted from one antenna that is received by another, and is a key parameter when installing antennas on platforms, such as aircraft. To avoid interference between systems connected to the antennas, the mutual coupling should be as low as possible. The risk for interference can be minimized in several ways; by designing the systems to be resistant to interference or to install the antennas in a way that makes the coupling between antennas low. This thesis focuses on the latter.Electromagnetic problems, such as finding the mutual coupling between antennas, can be calculated in simulations using commercial software. On large platforms, simulations become very computationally intensive. This thesis examines ways to efficiently calculate the mutual coupling between antennas on large platforms. The intention has been to develop methods that can be used in practical situations.One possible way to increase efficiency is to use appropriate approximations that simplify calculations. Two approximations have been evaluated; approximate wave propagation model and equivalent representations of antennas. Both of these approximations have the potential to reduced computation times, but suffer from the fact that the size of the errors introduced is not predictable. This contributes to an uncertainty in estimating the coupling between antennas that make them less interesting to use in applications. The reaction theorem, that describes the coupling as an interaction of electromagnetic fields, has been very useful in this work. Two novel formulations of the theorem have been derived that decompose fields into scattered components. It is shown that some of the components do not affect the reaction. The reaction theorem and the derived formulations have been used in two applications. The first application shows practical possibilities to calculate mutual impedance between two antennas installed on a common platform. It is also shown how the reaction theorem can be used to visualize coupling paths, which show how the coupling between the antennas is spatially distributed.The second application of the reaction theorem suggests an effective method for antenna placement on platforms that minimize the mutual impedance between antennas. The method enables field data to be reused, which significantly reduces the calculation time. Both suggested applications post-process electromagnetic field data. The field data can be determined with commercial software.The main results in this thesis are described in five articles and conference contributions that are or will be published in international scientific journals or at international conferences.