Design and Characterization of 10-Elements MIMO Antenna With Improved Isolation and Radiation Characteristics for mm-Wave 5G Applications

Abstract

A ten-elements MIMO antenna with improved isolation and reduction of X-polar radiation (XPR) in millimeter (mm) wave region is presented. The individual antenna element consists of stub loaded coplanar waveguide (CPW) structure with elliptical shaped radiator. Defected ground structure (DGS) has been incorporated by engraving partial elliptical shaped slots at the coplanar ground to reduce the mutual coupling effect between the adjacent antenna pairs of the MIMO. The backside of the substrate has a metallic plane with defects which is not connected to the coplanar ground of the antenna. This defected metal structure (DMS) acts as a reflector to improve the radiation characteristics by lowering of XPR as well as improving the co-pol to X-pol isolation. The proposed MIMO structure has a fractional bandwidth of 23.52% (22.5GHz-28.5 GHz) which entails the mm-wave 5G frequency spectrum n258 (24.25-27.5 GHz). The isolation| characteristics of the proposed MIMO antenna are below -35 dB over the operating bandwidth for any pair of adjacent antenna elements which imply significantly improved isolation between the adjacent antenna elements with highly compact layout area of 3.4λ × 8.5λ, where λ is wavelength corresponding to the mid-point of the bandwidth. The inter-element spacing of the MIMO structure is 0.44 λ. The main attractive feature offered by this structure is reduction of XPR in the operating frequency range thus improving the co-pol to X-pol isolation up to 20 dB and 28 dB in the boresight direction in both the XZ and YZ planes respectively. Furthermore, the co-pol to X-pol isolation is maintained above 15 dB almost throughout the elevation angular region -180° to 180° thereby negating the hindrance imposed by surface waves in mm-wave region. The diversity performances in terms of Envelope Correlation Coefficient (ECC), Diversity Gain (DG) and Channel Capacity Loss (CCL) are obtained as 0.1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> , 10 dB and 0.005 bps/Hz respectively which are within the acceptable limits. Mean effective gain (MEG) values with respect to the excited port 2 and port 3 is identical and approximately -3dB thus indicating the mean value of these two ports to be almost 1 dB. The multiplexing efficiency of the proposed MIMO antenna is satisfactory over the bandwidth. The group delay is investigated and found to be almost constant with a variation of 1.2 ns thus indicating linear phase characteristic of the antenna. The proposed structure is compared with other mm-wave MIMO antennas and found to be advantageous with respect to the number of antenna elements, compactness, low mutual coupling, co-pol to X-pol isolation, and ECC. A prototype of the proposed 10-elements MIMO is fabricated, and the measured results resemble with the simulated results.