On modeling and personal dosimetry of cellular telephone helical antennas with the FDTD code

A novel method to model helical antennas working in the normal mode, as well as helix-monopole antennas with finite-difference time-domain (FDTD) code is presented. This method is particularly useful to model antennas used for personal wireless communication handsets, where the fairly small dimensions of the helical antennas with respect to wavelength and the grid cell size do not allow an appropriate description of the antennas by the use of metal wires. By observing that a helix working in the normal mode is equivalent to a sequence of loops and dipoles, it is possible to model the helix as a stack of electric and magnetic sources with relative weights calculated using information obtained from analytical expressions for the far fields. Dosimetry associated with wireless telephones using helical antennas is then considered by calculating the specific absorption rates (SARs) induced by two actual devices in a 1.974/spl times/1.974/spl times/3.0-mm resolution model of the human head based on MRI scans of a male volunteer. Comparison of the computed results with experimental measurements in the near field, the far field, and the induced SARs shows good agreement.