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

全球正在研究在5ghz频段支持多媒体业务的新一代移动通信系统。相应的便携式终端将用于各种场合，例如带有无线调制解调器的便携式个人计算机（PC）。由于用户在使用时通常将PC机放在脸旁边，因此在天线设计中必须考虑安装在天线上的PC机与人体之间的电磁相互作用。然而，传统的时域有限差分法（FDTD）计算量大，难以应用于5ghz频段的天线设计。为了解决这一问题，我们将多网格时域有限差分法应用于5ghz频段天线的设计。在多网格时域有限差分法中，创建了粗网格区域和细网格区域两个区域。粗网格被用来模拟整个结构，细网格被用来模拟天线和体积，更多的是在人体中发生最高电磁吸收的地方。这样的安排是基于这样一个事实，即皮肤深度在5ghz频段非常小，因此电磁场只会穿透到表面组织。利用多网格时域有限差分法，对5ghz频段单极子PC机的结构进行了优化。结果表明，人体效应主要是阻挡天线向身体一侧的辐射。其对天线输入阻抗的影响不显著。另一方面，由于PC也是天线中有电流流动的部分，因此人体中电磁吸收面积最大的部分是离天线最近的部分或PC的角落。为了得到5ghz频段天线设计所需的人体模型复杂度标准，我们研究了一个基于解剖的人体模型和几个高度简化的人体模型。通过比较多栅格时域有限差分法计算的天线输入阻抗、辐射方向图和人体吸收功率，明确了考虑该频段电磁相互作用所需的人体复杂度。本研究的部分结果已发表在参考期刊上，并在国际研讨会上发表。少

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