Wideband tri-port MIMO antenna with compact size and directional radiation pattern

A wideband tri-port multiple-input-multiple-output (MIMO) antenna designed for worldwide interoperability for microwave access (WiMAX) and wireless local area network (WLAN) applications is presented. The proposed antenna is composed of three printed dipoles with an integrated balun, the size of which is only 0.08λ². By introducing ground stubs between adjacent elements, impedance matching is improved and mutual coupling is reduced. A bandwidth of 51.6% (2.30-3.90 GHz) with S₁₁ <;-10 dB and S₁₂, S₁₃ <;-10 dB is achieved, which can cover the whole three WiMAX bands and the 2.4 GHz WLAN band. Moreover, directional radiation patterns are achieved in these bands, and the average gain reaches 3.5 dB with up to 21.4 dB front-to-back ratio. The envelope correlation coefficient is below 0.038, which can provide good pattern diversity for a MIMO system.