Implementation of coded reflecting metasurface with dual-port MIMO antenna for circular polarization and gain enhancement

A novel dual port microstrip MIMO antenna having a minimal separation of 0.008λ0 between its both main radiating elements, is designed, analysed, fabricated and tested for modern wireless applications at 5.0 GHz, including WLAN applications. The proposed antenna consists of a 2-bit coded metasurface beneath its lower face which acts as an Artificial Magnetic Conductor (AMC). This surface reflects the backward radiation into the forward direction, which constructively adds to the main radiation and enhances the antenna gain from 4 dBi to 10.1 dBi. The proposed coded metasurface not only enhance the antenna but also it helps to create circular polarization. To design the proposed coded metasurface, a novel unit cell working at same frequency, is designed and investigated as a base element of the proposed metasurface reflector. This designed unit cell offers a good PCR (polarization conversion ratio) at the operating frequency. To design a 2-bit coded metasurface, four different codes (00, 01, 10, and 11) are assigned to different rotation angles of the unit cell based on the Pancharatnam-Berry (PB) phase theory. The proposed antenna offers 95% efficiency with very low ECC and perfect directive gain. A prototype model is fabricated to verify the simulated results. Various diversity parameters are analysed to confirm the MIMO characteristics, including ECC, TARC, and DG. Moreover, Channel Capacity Loss (CCL) is also analysed to show the utility of the channel. CCL is below the value of 0.2 bits/Hz/s at the operating band, makes the proposed antenna suitable for wireless MIMO applications including high-speed WiFi.