Design of a Planar EBG Structure to Reduce Mutual Coupling in Multilayer Patch Antennas

EBG structures have the ability of suppressing surface waves within a given frequency range. The purpose of this work is to use one of the simplest 2D EBG (a planar periodic structure made of metallic patches on a grounded dielectric slab) in patch antenna arrays to reduce mutual coupling. Also, we pretend to keep both the array element separation smaller than lambda₀ for grating lobes avoidance (as the work is focused on broadside arrays) and the patch antenna size large enough to have a good antenna directivity. To accomplish with this two conditions, the use of a multilayer dielectric substrate composed of high permittivity and low permittivity layers is fundamental. This allows the use of an EBG made of small elements printed on the high permittivity material and, at the same time, the low permittivity layer helps the bandwidth and the directivity of the antenna to be increased. A prototype has been manufactured and the mutual coupling has been measured. The reduction is larger than 10 dB with a completely planar structure.