This article proposes a four-port integrated antenna structure with a dielectric medium, which can be used to increase the pattern gain. To enhance the multiple-input-multiple-output (MIMO) performance, a low correlation is required between antenna elements. First, the refraction effect of the proposed medium is explained, including a derivation of the phase variation. Second, a new four-port integrated monopole antenna is proposed, which operates at 2.4 GHz and is appropriate for supporting a beamforming technique with high gain and small size. The proposed antenna can be useful for reducing correlation with the use of a dielectric medium to increase the pattern gain. This allows the achievable MIMO channel capacity to be increased to the ideal MIMO gain by increasing the pattern gain.