A Compact Dual-Mode Pattern-Reconfigurable Wearable Antenna for the 2.4-GHz WBAN Application

In this communication, a novel reconfigurable antenna operating at both ON- and OFF-body mode is proposed. Initially, the study is dedicated to the construction of omnidirectional and unidirectional radiation using the fundamental TM00 and TM10 mode of the rectangular patch. Then, a rectangular slot is cut out of the patch to shift the resonance of the unidirectional mode to a lower frequency, which not only minimizes the antenna's overall size but also enables the omnidirectional and unidirectional modes to have overlapping impedance bandwidths. In order to switch arbitrarily, four p-i-n diodes are mounted to control the operating mode. The measured results show that the overlapped bandwidth achieves 3.8% and could cover the 2.4-GHz ISM band. Besides, stable performance of the antenna is obtained when setting on different parts of the human body. The calculated specific absorption rate (SAR) values of both ON- and OFF-body mode meet the standards of the United States and Europe. These properties make the proposed antenna suitable for wearable systems.