An Eight-Port Circularly Polarized Wideband MIMO Antenna Based on a Metamaterial-Inspired Element for 5G mmWave Applications

This letter presents a low-profile, single-layer wideband metamaterial-inspired circularly polarized (CP) multiple-input–multiple-output (MIMO) antenna array. An 8 × 8 antenna array is manufactured on the Rogers RT/Duroid 5880 substrate with a partial ground plane. The dimensions of the proposed MIMO antenna array are 0.285
$\lambda$
× 0.11
$\lambda$
× 0.001
$\lambda$
at 28 GHz, where
$\lambda$
is the free-space wavelength. The isolation, gain, and higher axial bandwidth ratio are significantly improved by the introduction of a metamaterial-inspired element. As a result, the proposed circularly polarized MIMO antenna has an impedance bandwidth of 18 GHz, a mutual coupling of no more than
$-$
20 dB, an axial ratio bandwidth (ARBW) of 13 GHz, and a peak gain of 20.5 dBi. Significantly, the designated mmWave band (25–29.5 GHz) for 5G communication is covered by the operating bandwidth of the antenna. MIMO parameters are also discussed in terms of cross-correlation, diversity gain, and mean effective gain to further investigate the performance of the MIMO antenna. Therefore, the suggested antenna array is a good candidate for 5G new radio (NR) smart devices and sensors.