Decoupling Methods for Antenna Arrays

A variety of approaches are being employed to realize desirable high isolation levels between the antenna elements in densely packed arrays. This chapter illustrates the most widely used mutual coupling reduction strategies, i.e., electromagnetic bandgap (EBG) structures, defected ground structures (DGSs), neutralization lines, polarization rotators, decoupling surfaces, metamaterial structures, and parasitic resonators. Typical examples related to each of them are presented. In order to verify the decoupling effectiveness of the EBG structure between the two antenna elements, two pairs of microstrip antenna arrays with and without the EBG structure were fabricated and measured. Neutralization lines can be added between the array elements to compensate for the existing complex electromagnetic coupling pathways. The reflecting elements in the array-antenna decoupling surface can be classified into two types based on their functionality: the primary reflectors and the secondary reflectors. Another form of decoupling occurs naturally from the electromagnetics theory point-of-view, i.e., two orthogonal polarization states.