Compact Dual-Band MIMO Antenna with High Isolation using Small Common Decoupling Ground

A compact planar dual-band multiple-input multiple-output (MIMO) antenna with a high isolation is presented in this letter. In the microwave (MW) band, two symmetrical planar meandered microstrip monopoles, which utilize small rectangular metal sheets as the MW ground, are designed to achieve a high realized gain of more than 4 dBi in an ultra-wide band of 4.1-7.3 GHz. To further increase the aperture reuse efficiency of the MIMO antenna, a high-gain millimeter-wave (MMW) patch array is introduced to form a compact dual-band design. Unfortunately, due to the introduction of the MMW array, the couplings between different ports increase, especially for the two MW ones. Without introducing extra decoupling structures, a small common decoupling ground is constructed to effectively increase the isolation among different ports, from 15 dB to 35 dB. The mechanism of the small common decoupling ground is studied and the antenna characteristics are analyzed. Both simulation and measurement verify that the proposed high-isolation dual-band antenna has a high realized gain, a low envelope correlation coefficient (<0.03), and high efficiencies.