Dual-Band Dual-Mode Button Antenna for On-Body and Off-Body Communications

TLDR

The paper introduces a dual‑band, dual‑mode button antenna for body‑centric communications and examines its specific absorption rate (SAR) compliance. The antenna employs a spiral inverted‑F design for the lower band to provide omnidirectional on‑body radiation, and a high‑order mode inverted‑F with a metal reflector for the upper band to achieve broadside off‑body radiation; a prototype was built and its transmission between two mounted antennas was measured. Measurements on a phantom show lower‑band gain of –0.6 dBi and efficiency 46.3 %, upper‑band gain of 4.3 dBi and efficiency 69.3 %, a maximum transmit power of 26.4 dB·m under 1.6 W/kg SAR, and overall miniaturization that makes the antenna suitable for clothing‑integrated WBAN use.

Abstract

A dual-band dual-mode button antenna for body centric communications is presented. At the lower band, a spiral inverted-F antenna is designed with omnidirectional radiation pattern for on-body communication. At the upper band, the high-order mode of the inverted-F antenna is utilized together with a metal reflector to realize broadside radiation for off-body communication. For demonstration, a prototype is implemented. The measured peak gains on the phantom at the lower and upper bands are -0.6 and 4.3 dBi, respectively. The antenna operating on the phantom has measured efficiencies of 46.3% at the lower band and 69.3% at the upper band. The issue of specific absorption rate (SAR) is studied. The maximum transmitted power under the SAR regulation of 1.6 W/kg is found to be 26.4 dB·m, which is high enough for body centric communications. In addition, the transmission performance between two proposed antennas mounted on the body is investigated by measuring the transmission loss. With an overall miniaturized size, the robust button antenna could be integrated in clothes and be a potential candidate for wireless body area network applications.