Partially Omnidirectional and Circularly Polarized MIMO Antenna Covering Sub-6-GHz Band for 5G Fast Plan

A two-port multiple-in multiple-out (MIMO) antenna is designed, manufactured, and analyzed, which covers the whole sub-6-GHz band ranging from 0.97 to 6.19 GHz with an integrated circularly polarized wideband centered at 3.5 GHz. The proposed work overcomes the challenges of 1) large size of antennas at
${L}$
-band; 2) circular polarization (CP) for wideband; 3) channel capacity for fifth-generation (5G); 4) diversity in MIMO; and 5) minimum mutual coupling with inbuilt isolator. A very small antenna size of
$0.113\lambda _{0} \times 0.129\lambda _{0}$
is obtained after incorporating several techniques, including slots, stubs, defected ground, and parasitic elements. The structure is simple and contains an in-built isolator that provides more than 23 dB isolation between both ports. Partial ground with additional stubs helps to maintain high isolation between both ports within the whole operating band. The proposed antenna also improves the channel capacity and provides the minimum channel capacity loss (CCL) of about 0.12 bits/s/Hz. Various diversity characteristics [e.g., envelope correlation coefficient (ECC), total active reflection coefficient (TARC), diversity gain (DG)] are analyzed and found suitable within the required range. The proposed antenna radiates the omnidirectional pattern at the
${L}1$
(1.57 GHz) and
${L}2$
(1.22 GHz) bands of the global positioning system (GPS). Other than
${L}1$
and
${L}2$
bands, the proposed antenna also offers wide beamwidth for the remaining bands. Finally, an antenna model is manufactured to validate the findings through experimental measurements.