Extension and validation of the equivalent sources helical antenna modeling with the FDTD code

The finite-difference time-domain method (FDTD) is currently the most used numerical technique for dosimetry of wireless devices. A concern is that the structurally complex antennas might not be modeled accurately. Specifically, helical antennas are often used and these are incompatible with rectangular grid FDTD without resorting to staircase approximation of the antenna geometry. We have introduced in a previous publication (see IEEE Trans. Antennas and Propagation, vol.45, p.525-30, 1997) a new method to model small diameter normal mode helical antennas with the FDTD code for cellular telephone applications. This approach, that uses equivalent electric and magnetic sources to model the helix, has however not been previously tested for cases where the diameter of the helix may be more than two times the grid size. In this paper, we present a modified weighted equivalent source method and its experimental validation for these larger diameter helical antennas. The test case presented in this paper has been suggested by the IEEE Standards Coordinating Committee SCC-34 as a benchmark test to validate the modeling capabilities of the FDTD code for helical structures.