A $4\times 4$ Millimeter-Wave Antenna Based on a Higher Order Mode in a Sub-mode Microwave SIW Strucutre for Recent 5G Applications

This paper presents a single structure, multi-port antenna for 5G millimeter wave (mmWave) applications. The proposed antenna is constructed by exploiting the higher-order modes of a fraction-mode microwave substrate-integrated waveguide (SIW) cavity at 28 GHz (quadrature mode substrate-integrated waveguide (QMSIW)). Such properties exhibit spatial multiplexing capabilities, giving the single cavity a MIMO capability. Firstly, two perpendicular T-shaped microstrip ports (Port 1 and Port 2) are installed to excite TE205 higher-order mode of the QMSIW cavity at 28 GHz. To extend the MIMO capability, a 4×4 MIMO QMSIW antenna is created by adding two extra coaxial feeding ports (Port 3 and Port 4), the higher-order modes of the cavity are reused by leveraging two orthogonal inverted L-shaped slots, in which each slot is excited using coaxial cables at 28 GHz. The proposed antenna exhibited a wide -10 dB impedance and > 11 dB isolation based on the simulation environment without using decoupling structures. Finally, we believe this work offers a promising contribution to present and future multi-port single antenna, MIMO, and polarization applications.