A Study on Antenna Design Method for 5 GHz Band Portable Terminals

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A new generation of mobile communication systems is being worldwide investigated at 5 GHz band for supporting multimedia services. The corresponding portable terminals will be used in a great variety of situations such as a laptop personal computer (PC) with a wireless modem. Since users generally have the PC next to their face in use, it is essential to consider electromagnetic (EM) interaction between the antenna mounted PC and human body in the antenna design. However, conventional computer tools such as the finite-difference time-domain (FDTD) method are difficult to apply for the antenna design at 5 GHz band because of its heavy computation burden. To cope with this problem, we have applied a multi-grid FDTD method for the 5 GHz band antenna design. In the multi-grid FDTD method, two regions consisting of the coarse-grid region and fine-grid region were created. The coarse grids were used to model the entire structure, and the fine grids were used to model the antenna and the volu … More me in the human body where the highest EM absorption occurs. Such an arrangement was based on the fact that the skin depth is very small at 5 GHz band so that the EM fields will only penetrate into the superficial tissue. Using the multi-grid FDTD method, we have optimized the structure of a monopole mounted PC at 5 GHz band. The results indicated that the human body effect was mainly blocking the antenna radiation towards the body side. Its influence on the antenna input impedance was insignificant. On the other hand, since the PC was also a part of the antenna where currents flow, the highest EM absorption area in the human body was in the part closest to the antenna or the PC corner. To derive a criterion for the complexity of human body model required in the antenna design at 5 GHz band, we have investigated an anatomically based human body model and several highly simplified human body models. Via comparing the multi-grid FDTD calculated antenna input impedance, radiation pattern and power absorbed by the human body we have clarified the required human body complexity for considering the EM interaction at this frequency band. One part of the results in this study has been published on a referred journal and presented at international symposiums. Less