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A novel circularly polarized button antenna is proposed. The antenna is constructed on a disc shaped FR-4 substrate. This disc is located on top of a textile layer and supported by a feeding probe. The antenna works in the 5.47-5.725 GHz U-NII world wide band, with over 14% relative impedance bandwidth and over 7% relative axial ratio bandwidth. A prototype has been fabricated and measured. A good agreement is found between measured and simulated results.

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A dual-band dual-polarized wearable array is proposed, based on a miniaturized innovating button radiator topology. The diameter of the rigid button is only 19.5 mm (0.29 λ at 4.5 GHz), which optimizes the users' comfort, and makes it the smallest up to date in literature. The operational bands are 4.50-4.61 GHz and 5.04-5.50 GHz. The antenna thus covers the 4.5-4.6 unlicensed future 5th generation (5G) communication band for the internet of things (IoT), and the 5.1-5.5 GHz wireless local area network (WLAN) band, respectively. Two orthogonal linear polarizations are obtained in each band. A low mutual coupling between the button antenna elements (below -18 dB) and between the two ports within each element (below -20 dB) is achieved, guaranteeing a good diversity performance. The envelope correlation coefficient (ECC) and the specific absorption rate (SAR) performance are also analyzed. In order to demonstrate the robustness of the button antenna and to mimic realistic situations, a more complicated asymmetrical ground plane model of the button antenna is studied for the first time. A prototype of a two-element button array has been fabricated. The measurement results match well with the simulations. A 10-element button array is studied within the context of a 3-D channel model, taking into account the button element's radiation pattern. A high achievable spectral efficiency (SE) is obtained.

The mutual coupling in small wearable multi-antenna systems under bending conditions is studied. Two conventional passive mutual coupling suppression approaches, involving electromagnetic bandgap (EBG) structures and defected ground structures (DGS) are investigated when curving or deforming. To overcome the limitations of those traditional isolators in on-body applications, a novel metamaterial-inspired isolator which combines DGS and modified split ring resonators (SRR) is proposed. It avoids any vertical conducting parts, which have a high risk of being broken with time due to movements of the user. On top, it is wideband, with stable isolating performance under complex bending conditions, and does not affect the compactness of a linear array. The envelope correlation coefficient (ECC) between the two on-body antennas, when the proposed isolator is present, is found to be low, which is important for a better throughput for a multiple-input-multiple-output (MIMO) system. A prototype was fabricated and measured to prove the validity of the new concept.

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