Decoupling networks composed of lumped elements for diversity/MIMO antennas

We show design equations for decoupling networks composed of lumped elements. These equations are valid for arbitrary two-element antenna arrays and plane-symmetrical three-element antenna arrays. The decoupling networks consist of series susceptances and shunt susceptances. We design small two-element and three-element antenna arrays with the decoupling networks, and verify the design equations by performing measurements and simulations. The sizes of the two-element and three-element antenna arrays including the ground planes are 0.12λ_c × 0.18λ_c and 0.25λ_c × 0.21λ_c, respectively. We confirm high isolation is achieved by the decoupling networks.