Computer simulation of the human-body effects on a circular-loop-wire antenna for radio-pager communications at 152, 280, and 400 MHz

In radio-paging communications, the internal antenna of a pager is usually a loop antenna, and its radiation characteristics are strongly influenced by the human body due to the very close proximity. This paper presents an extensive computer simulation of the influence of the human body on a ciruclar-loop-wire antenna to simulate the pager antenna. The coupled integral equations (CIE's) approach and the method of moments (MoM) are employed for numerical simulation of this antenna body-coupling problem. The magnetic frill source is used to model the antenna-feeding structure. A realistically shaped full-scale human-body model (1.7 m) is constructed. A small loop antenna (loop radius b = 1.7 cm and wire radius a = 0.072 cm) of x, y, and z orientation, in free space or proximate to the human body at the top pocket (chest position) or belt level (waist position), is considered. Numerical results of the antenna characteristics and body absorption at 152, 280, and 400 MHz are presented and discussed for radio-paging applications. At 280 MHz, it is found that the real part of the impedance increases about five to ten times, and, hence, the antenna ohmic-loss radiation efficiency increases from 17% (in free space) to 69%, 44.3%, and 58.4%, respectively, for the x-, y-, and z-oriented loops when proximate to the body. The radiation efficiencies, reduced by the body-absorption effect, are 5%, 61%, and 25% for the x-, y-, and z-oriented loops, respectively. For the y-oriented loop, which is found to be the most suitable for paging communications, the antenna efficiencies are almost the same at the two location levels for all frequencies considered. Compared with the body-absorption radiation efficiency (reduced due to the antenna-radiated power absorbed by the body) at the 280- (68%-70%) and 400-MHz band (65%-67%), the 152-MHz band has the smallest efficiency (39%) and the highest body-absorption rate (61%). This may be due to the reason that it is close to the second resonant frequency of a human body (170 cm) in free space. The computed antenna characteristics influenced by the human body, including the input impedance, antenna patterns, cross-polarization field level, radiation efficiencies, and maximum and minimum power gains, are important for the antenna/RF design and the link-budget consideration of the radio-paging communication system.