Compact Highly Directive MIMO Vivaldi Antenna for 5G Millimeter-Wave Base Station

In this paper, a novel design for a 5G base station (BS) antenna is proposed. The proposed antenna consists of two orthogonally polarized antennas. The two antennas are modified compact Vivaldi antennas operating in the two recommended 5G operating bands; 28 and 38 GHz with measured impedance bandwidth of 26.5–40 GHz. The orthogonality of the two antennas allows the use of two antennas on the same substrate within one enclosure to serve two sectors separately. So, instead of using two enclosures to serve two sectors, only one enclosure is required. The two elements may be part of two separate MIMO distributions. To minimize the isolation between the MIMO antennas elements with low complexity and low cost, the antenna elements have been distributed along the z-direction with half-wavelength spacing between elements including Electromagnetic band-gap (EBG) structure in between them. The simulation results have been shown that the measured mutual coupling between the array elements is improved from − 32 to − 45 dB at 28 GHz and from − 22 to − 59 at 38 GHz. The envelope correlation coefficient (ECC) is enhanced and the diversity gain (DG) is improved simultaneously. The suggested structure has been designed on CST Microwave Studio 2019. The two orthogonal antennas’ overall size approaches 34 mm × 55.8 mm × 0.203 mm3. The measured gain of the suggested design is enhanced from 10.4 to 12.8 dB at 28 GHz whereas a minor change is noticed at 38 GHz. The maximum simulated radiation efficiency approaches 96%. The antenna is fabricated and tested where good experimental results are noticed compared to the simulation results.