A Compact Two-Element Linearly and Orthogonal Circularly Polarized MIMO Antenna System for 5G Cellular and WLAN/Wi-Fi 6E Application

This paper presents the design, analysis, and experimental validation of a compact
$2 \times 1$
MIMO antenna operating in two bands. Band 1 is Linearly Polarized (LP) with spatial diversity operating in the sub-6 GHz band for the Fifth Generation (5G). Band 2 is Circularly Polarized (CP) for polarization and pattern diversity with an axial ratio below 3 dB for WLAN, Wi-Fi 6E, and C-band applications. The proposed single antenna consists of a Squared Shape Modified Monopole with partially Defected Ground (SMMDG) fed by Co-Planar Waveguide CPW. The partial ground has a defect on its upper left side and an I-shaped strip on the right side. The two MIMO radiators are arranged in oppositely flipped shapes. The decoupling and common partial ground structure consists of an opposite, Double T-shaped strip (DTSS) with a common strip head that performs as a band-stop filter. The overall dimensions of the MIMO antenna are
$31.5\times 45 \times 1.6$
mm3. The simulated impedance bandwidth of the first band with LP lies between 3.1 and 4.7 GHz, for which
$\text{S}_{{11}}$
and
$\text{S}_{{22}} < -10$
dB, while the measured values are between 3.45 GHz and 4.8 GHz. The simulated impedance bandwidth for the second band for
$\text{S}_{{11}}$
and
$\text{S}_{{22}} < -10$
dB lies between 5.24 and 7.9 GHz, while the measured one lies between 5.65 GHz and 9 GHz. The simulated 3-dB Axial Ratio Bandwidth (ARBW) within Band 2 is (5.6–8.5) GHz, while the measured 3-dB ARBW is (5.95–8.1) GHz. The minimum simulated isolation between the two ports is 17 dB in Band 1 and 26 dB in Band 2, while the minimum measured isolation is 21 dB in Band 1 and 26 dB in Band 2. Wi-Fi 6E (n96) (5.925-7.125) GHz is covered with right-hand circular polarization (RHCP) in the positive Z direction and left-hand circular polarization (LHCP) in the negative Z direction, covering Band 2 with an axial ratio less than 3 dB. Other crucial MIMO metrics are also calculated, such as the Envelope Correlation Coefficient (ECC), Mean Effective Gain (MEG), and Diversity Gain (DG). The antenna provides excellent MIMO diversity performance, which makes it an excellent candidate for many portable wireless applications.