SAR and radiation performance of balanced and unbalanced mobile antennas using a hybrid computational electromagnetics

The procedure that is required to ensure that the effect of the mobile antenna on the handset can be reduced by using balanced antennas was investigated. However, using this type of antenna may degrade the antenna performance, such as bandwidth and gain, although these antennas can cause less effect on the body to which they are adjacent. Moreover, if these antennas are well-designed, then the maximum specific absorption rate (SAR) values are likely to be reduced when placed next to the human head, since the coupling of such antennas to the body of the handset is very weak. In this paper, a study on balanced and unbalanced antennas for mobile handsets next to the human head is presented, using a hybrid electromagnetic method for the analysis. The method uses the hybridisation technique between the frequency domain Method of Moments (MoM) and the Finite Difference Time Domain method (FDTD). The antenna was modelled using MoM whereas the head tissues were modelled using FDTD. Two antennas were designed and investigated with respect to the SAR and radiation performance for two different antenna positions on the top edge of mobile handsets. Radiation patterns are presented and compared, with and without the human head, and the maximum SAR values and field distribution inside the human head for both antennas are discussed. The balanced antenna shows good improvements with respect to the unbalanced antenna in terms of the SAR values and variations of the input impedances