Radiation characteristics of an antenna for a small radio terminal in vicinity of a human body

In this paper, a design guideline is presented for an antenna for a small radio terminal placed in various locations on a human body. Typical installation conditions include wearing it on the chest and holding it by hand. The radiation patterns in the vertical plane of a λ/4 monopole antenna for a card-type terminal attached to a human body are measured at 2 GHz. When it is worn on the chest, the efficiency changes significantly between 18 and 80% if the spacing between the antenna and the chest is 10 to 35 mm. Since the radiation in the vertical plane in front of the human body has a null in the horizontal plane as in free space, the pattern averaging gain (PAG) has a low value of less than −8 dBd. On the other hand, when it is operated in the hand, the efficiency is constant at about 60%. Unlike the case in free space, the radiation pattern in the vertical plane shows strong radiation in the horizontal direction so that the PAG is as high as about −4 dBd. Next, by means of the FDTD method, the effects of various human body parts on the radiation characteristics are analyzed. When it is worn on the chest, both the power absorption and the radiation pattern are dominantly influenced by the trunk of the body. Hence, in the analysis and measurement, only the trunk needs to be taken into account. When it is operated in the hand, the power absorption by the hand and arm and the reflection from the head and trunk are dominant. It is therefore necessary to take into account the entire upper body in the analysis and measurement. © 2002 Scripta Technica, Electron Comm Jpn Pt 1, 85(6): 1–10, 2002