Numerical computation of human interaction with arbitrarily oriented superquadric loop antennas in personal communications

Loop antennas are widely used in many personal communication systems such as radio pagers. This paper presents results from an extensive numerical simulation of the human interaction with loop antennas. The loop antenna with a superquadric curve, which is able to model the circular, ellipse, square, and rectangular loop is used to model the rectangular loop antenna with rounded corners. 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. The coupled integral equations (CIE) approach, which consists a Pocklington-type integral equation (PIE) for the loop antenna and a volume electric field integral equation (VEFIE) for the body with mutual coupling terms, are developed to numerically study this electromagnetic (EM) coupling problem. The method of moments (MoM) is employed for numerical solution. Numerical results for the antenna located at the chest pocket and waist-belt levels of the human body with arbitrary loop orientations are presented at 280-MHz VHF paging band. The pager's internal rectangular loop antenna with rounded corners is modeled by a superquadric loop antenna. It is found that the real part of the impedance (radiation resistance) increases about five times and, hence, the antenna ohmic-loss radiation efficiency increases from 4% (in free-space) to 33, 17, and 26% for the chi-, y-, and z-oriented loops when proximate to the body. The radiation efficiencies, reduced by the body absorption effect, are 13, 40, and 27% for the chi-, y-, and z-oriented loops, respectively. For the y-oriented loop, which is found to be the most suitable for radio-paging communications, it has the highest value of E-theta average power gain (product of the directive gain and the ohmic-loss and body-absorption efficiencies) in the horizontal plane. The computed antenna characteristics influenced by the human body, including the input impedance, antenna patterns, cross-polarization field level, radiation efficiencies, and maximum/minimum and average power gains, are very useful for the antenna/RF design and the link budget consideration of the personal communication systems.