Reduction of Mutual Coupling Between Closely Spaced Patch Antennas Using Dielectric Contrast Techniques

Abstract

Phased array antennas require a distance of the array elements to be smaller than half a wavelength in order to avoid grating lobes while scanning through the whole visible space. In the case of planar dual- or multi-band antenna arrays, the capability of wide-angle scanning at the operational bands defines strict constraints on the electrical inter-element spacings, especially at the low frequency band. For patch antenna arrays, these requirements lead to the formation of closely-spaced antenna elements and thus, increased levels of mutual coupling. This thesis aims firstly on understanding the physics of mutual coupling phenomenon between closely-packed patch antenna elements by investigating the behavior of different field/power components that are associated with the space, surface and total waves obtained from some simplified analytical models of patch antennas. The second aim of the thesis is to decrease mutual coupling between antenna elements by using dielectric contrast techniques. To reach this aim, different vertical/lateral dielectric stratifications inside the homogeneous substrate have been investigated and applied to reduce the mutual coupling while having no negative impact on the scanning performance, radiation pattern characteristics or radiation efficiencies. The performance of the MATLAB-based mathematical model has been evaluated both via theoretical analysis and FEKO/CST simulations. The simple model has shown great potential to explain the origins of mutual coupling and to be used for optimization purposes in the vertical stratification technique. More detailed analysis and optimization have been performed in CST in order to understand the limits and capabilities of vertical/lateral dielectric stratification. The results of the simulations have shown that by proper selection of the position, permittivity and thickness of the additional high-permittivity layer, it is possible to achieve satisfactory performances in terms of mutual coupling for E-plane arrays. Furthermore, a novel four-layer substrate design has been proposed that combines high and low permittivity layers and is able to decrease mutual coupling in E-plane while improving the efficiency without any need to redesign the array topology.