Circularly/Linearly Polarized Low-Profile Plasma Microstrip Antenna for MIMO Applications

A polarization reconfigurable square microstrip patch antenna (SMSPA) based on plasma is introduced in this paper. The antenna is designed for mobile base-stations in 4G/5G wireless networks in sub-6-GHz band. The polarization reconfigurability is achieved by etching two assymertical plasma boxes in the SMPA along its diagonal. A parametric study on the plasma boxes sizes and positions and their effect on the polarization response of the SMSPA is introduced. The single antenna has an overall size of 96 × 96 × 4.6 mm3 (0.78λo × 0.78λo × 0.0377λo where λo is calculated at the operating frequency). A high gain of 5.8 dBi is radiated at 2.4 GHz. The antenna dimensions are optimized for achieving a minimum axial-ratio of 0.608 dB at 2.44 GHz. Different circular and linear polarization states are achieved, case (1) and case (2) for left-hand and right-hand circular polarization (CP), while case (3) and case (4) for linear polarization. MIMO structures consiststing of 1 × 2 and 2 × 2 SMSPA elements with high isolation are designed and investigated. The overall dimensions of the proposed 4-port (2 × 2) MIMO antenna are 160 × 160 × 4.6 mm3. The MIMO antenna layout guarantees compact size with spacing 0.25λo (30.5 mm) between elements and high isolation of 22.44 dB is achieved. The envelope correlation coefficient (ECC) lower than 0.015 between elements with a diversity gain of 10 over the operating frequency bandwidth is acheived.