MIMO antennas using controlled orthogonal characteristic modes by metal rims

A metal-rimmed multiple-input multiple-output (MIMO) antenna design operating below the 1 GHz frequency band is proposed that offers a wide bandwidth, high isolation, low correlation, and compact size. The proposed technique is based on metal-rimmed mobile phones with four gaps, and the overall design occupies a small size in the ground plane. Orthogonal ground mode resonances are controlled to be equal to the operating frequencies, providing high antenna performance and good diversity performance. The proposed main antenna is achieved by utilizing the upper-side rim to tune the ground mode resonance along the length of the ground plane to be equal to the operating frequency; moreover, a coupling slot couples strongly with the ground mode resonance to achieve a -6 dB bandwidth from 0.695 to 1 GHz (305 MHz). The orthogonal ground mode along the width of the ground plane is used for diversity antenna design. Similarly, the ground mode resonance is made equal to the operating frequency by controlling the left-side metal rim such that a simulated -6 dB bandwidth from 0.850 to 0.920 GHz (70 MHz) is achieved. The simulated isolation is more than 11.5 dB in the operating band, and the measured envelope correlation coefficients is below 0.1.