A study of the effects of the shoulder on the effective gain characteristics in the multiple radio wave environment of a dipole antenna close to a human head

Abstract

When a portable telephone is used close to a human head, the handset and the shoulder are in close proximity because the shoulder is raised. Thus, the shoulder could influence the antenna characteristics of the handset. However, there have been few reports dealing with such effects. This paper describes a basic study of the effects of the shoulder on the impedance and radiation characteristics of a half-wavelength dipole antenna located near the head at 900 MHz. Further study shows that there is a change in the mean effective gain (MEG) in a multiple radio wave environment, and the mechanism by which this change is effected in relation to antenna location and polarization is clarified. The wire-grid method is employed in modeling the human body as a cylindrical head and a trapezoidal left shoulder. Studies were also conducted using a dipole antenna close to a homogeneous human phantom and an adult man. The analysis of MEG is verified through indoor RFM measurements. The analytical and empirical results indicate that when the dipole antenna is in a horizontal position the radiation to the shoulder is suppressed and consequently a greater radiation intensity at the higher elevation angles of radio signal arrival is obtained due to the presence of the shoulder. This effect results in MEG values 0.8 to 2 dB greater than those obtained from the human model without a shoulder. These facts suggest that the presence of the shoulder should be taken into account when an adequately accurate evaluation of the radiation characteristics of portable telephone antennas is needed, since portable telephones are commonly near the horizontal orientation in the usual talk position. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 84(1): 21–30, 2001