In this dissertation, not only the antenna and antenna array design techniques for fourth-generation mobile communication system are proposed, but also the specifications related to antenna bio-compatibility are studied. At first, two dual-wideband design techniques suitable to be applied for laptop computer applications for LTE/WWAN and LTE MIMO operations are proposed. The techniques can also be applied to internal tablet computer antennas. The isolation issues of MIMO antenna array of different mobile communication devices, such as laptop computer, tablet computer, and mobile phone, are then discussed. Finally, an analysis of body SAR for tablet computer applications are given and discussed.