Integration of Sub-6 GHz and mm-Wave Antenna for Higher-Order 5G-MIMO System

An extremely low-profile/compact MIMO system is proposed by utilizing the dual antenna for 5G sub-6 GHz and mm-wave application. The antennas are integrated on a centrally located square-shaped slot-loaded octagon-shaped substrate board area of 3706.69 mm2. The identical dual antenna elements with the same orientation are orthogonally placed on an octagon-shaped substrate from the outer side, creating an 8-element MIMO antenna for sub-6 GHz application. From the inner side of the same substrate, a
$1\mathbf {\times }4$
array-based antenna is orthogonally placed in front of the remaining side of the octagon, forming a 4-element MIMO antenna for mm-wave application. The edge-to-edge separation between element-1 and -9 is almost close to
$\lambda _{0}$
/64 (
$\lambda _{0}$
at 4.0 GHz). The stubs are connected to shared ground plane to reduce the coupling between closely placed antenna elements. The MIMO system provides dual −6 dB impedance bandwidth of (
$S_{ij}{}_{\,\,} \mathbf {\mathrm {\in }}\,\,{i} = {j}$
, 1 to 8) 4.0–5.6 GHz and (
$S_{ij}{}_{\,\,} \mathbf {\mathrm {\in }}\,\,{i} = {j}$
, 9 to 12) 24.25–29.5 GHz, can cover the 5G n79//n257/n258 bands. It has a minimum isolation (
$S_{ij~}\mathbf {\mathrm {\in }}~{i} \mathbf {\mathrm {\ne }} {j}$
) value of 12 dB and 22 dB, respectively. Also, the peak gain and total efficiency values for element-1 and -9 are 5.4 dBi and 8 dBi, and 56.5–77.4% and 70.3–96.2%, respectively. The measured and simulated results are found in close agreement those confirming that the proposed MIMO system may be a suitable candidate for 5G-smartphones. Due to 0.508 mm low-profile, antenna is integrated within the back cover of smartphones, thereby inside device volume will reduce.