Edinburgh Napier University

  In this paper, a reconfigurable Multiple-Input Multiple-Output (MIMO) antenna array is presented for 5G portable devices. The proposed array consists of four radiating elements and an Electromagnetic Band Gap (EBG) structure. Planar monopole radiating elements are employed in the array with Coplanar Waveguide Ports (CWPs). Each CWP is grounded on one side to a reflecting L-shaped structure that has an effect of improving the antenna’s directivity. It is shown that by inductively connecting Minkowski fractal structure of 1 st order to the radiating element, the impedance matching is improved that results in enhancement in the array’s bandwidth performance. The EBG structure is used to provide the isolation between antenna elements in the MIMO array. The fractal structure is connected to the L-shaped reflector through four photosensitive light dependent resistor (LDR) switches. The effect of various LDR switching configurations on the performance of the antenna is investigated. The proposed array provides a novel performance in terms of S-parameters with enhancements in the radiation properties. Such enhancements are achieved with low separation gaps between antenna elements (about λ o /16 at 3.5 GHz). It is shown that the array’s operational bands centered at 3.5 GHz and 4.65 GHz can be selected by activating certain LDR switches. The electromagnetic exposure of the array on the human body is investigated by determining the specific absorption rate (SAR). It is found that the proposed antenna shows lower SAR values compared to other antennas reported in literature. With the proposed EBG structure, the gain of the array is increased 7.5 dB (from -3.5 dBi to +4 dBi) at 3.5 GHz and by 14.3 dB (from -8.7 dBi to + 5.6 dBi) at 4.65 GHz. The average radiation efficiency between 3.5 GHz and 5.5 GHz increased by 42% from 20% to 62%. Excellent radiation characteristics of the EBG the array makes it suitable for 5G portable devices such as tablets.