This paper proposes a periodic structure to improve isolation using ferrite materials for small controlled reception pattern antenna arrays. The periodic structure is composed of metal and ferrite plates with high permeability, and the ferrite material is used as a replacement of the perfect magnetic conductor in the soft surface to reduce the size of the corrugated geometry. This structure improves the isolation between array elements by eliminating the tangential components of electric and magnetic fields on the surface of metal and ferrite plates, respectively. The result shows that the proposed structure is capable of improving the isolation in extremely small arrays.