Mutual coupling (MC) between elements in an antenna array could significantly affect antenna performance, but this effect has rarely been reported for circularly polarized (CP) antennas. Therefore, this paper investigates a wideband CP multiple-input-multiple-output (MIMO) antenna operating between 1.8 and 2.6 GHz. A line patch was introduced between closely placed radiating elements ( 0.3\lambda ) to produce a high isolation between elements in the proposed antenna. The designed MIMO antenna has a wide impedance bandwidth, a wide axial ratio (AR) bandwidth, a very low MC ( \text{S}-{{21}} < -25 dB), a low envelop correlation coefficient (ECC < 0.01), a high diversity gain (DG 10 dB), and a realized gain of above 2 dB over the entire frequencies. The prototype of the proposed antenna geometry was fabricated and measured. A good agreement between the simulated and measured results was observed.
