EFFECTS ON PORTABLE ANTENNAS OF THE PRESENCE OF A PERSON

This paper deals with the influence the presence of a person has on th e performance of antennas for hand-held portable telephones. It is sho wn how input impedance, far-field radiation pattern, radiation efficie ncy, and the magnitude of the near field are affected by the presence of the human body. The investigations have been carried out by applyin g the finite difference time domain technique to a model of the teleph one with a lambda/4 monopole antenna and a simple hand-head model of t he operator. Results from this configuration are compared with results for the telephone box and antenna alone. Measurements have been perfo rmed to verify the results obtained by simulations. The results show t hat a shadow effect in the far-field pattern occurs in the direction o f the person and that the radiation pattern, including polarization, c hanges considerably from the telephone with the antenna alone. The imp edance results show a change in resonance frequency when the telephone is placed next to a person. Results for radiation efficiency show tha t close to half of the energy is absorbed by hand and head. On average a system loss of 3-4 dB should be included in a link budget, and ther e is considerable fading, even in a radio-anechoic chamber, when perso ns move around in a natural manner.