Experimental and FDTD-computed radiation patterns of cellular telephones held in slanted operational conditions

The objective of this paper is to investigate, numerically and experimentally, the radiation patterns of various commercial cellular telephones held in a realistically slanted position relative to the head, to understand the performance of such devices for normal use conditions. The investigation has been performed with and without the human head model at an angle of 30/spl deg/ with respect to the vertical. To avoid the stair-step modeling of the cellular telephone for the finite-difference time-domain (FDTD) formulation, the head has instead been tilted forward by 30/spl deg/ and a transformation of coordinates in the FDTD calculation has been used to obtain the desired vertical and horizontal polarizations. We show that the FDTD method gives results that are in good agreement with measurements, both for shape and gain of the radiation patterns, for all of the considered mobile telephones that use several types of antennas. Generally, a decrease of the cellular telephone gain for the vertical component of the field has been observed as compared to the vertical configuration of the telephone and also a decrease in gain is obtained when the phone is held against the human head. Furthermore, it is shown that the FDTD method is capable of providing fairly accurate results even for radiation patterns at a slanted angle and modeling of realistic cellular telephones.