A Triband Circular-Polarized Four-Port MIMO Antenna With Compact Size and Low Mutual Coupling

This letter presents a compact triband circular polarized (CP), multiple-input–multiple-output (MIMO) antenna by using the ground plane excitation technique, where four simple E-shape meander lines are designed at the top of the low-cost substrate. The electrical dimensions of the proposed four-port MIMO antenna are 0.33λ ×0.33λ ×0.012λ, where (λ) is the free-space wavelength at the lower operating frequency. The prototype is intended to be single-layered and manufactured on the FR-4 substrate. The MIMO antenna covers the impedance operating bands of 2.14 GHz to 2.49 GHz, 3.4 GHz to 3.81 GHz, and 4.7 GHz to 6.6 GHz, with the isolation of≥18.2 dB,≥23 dB, and≥27 dB, respectively. The CP properties and isolation are achieved by the installation of an optimized special connected ground plane. With the help of this technique, the axial ratios are obtained below 3 dB at the required operating frequencies. The simulated and measuredS-parameters, axial ratios, radiation patterns, gain, and efficiency agree with each other and have better results. The diversity parameters are also calculated and have an acceptable value in both simulated and measured. The proposed MIMO antenna is a good candidate for wireless local area network and worldwide interoperability for microwave access.