This paper presents a polarization-controlled active antenna applied to BAN on-body communications. A primal objective is to achieve the enhancement of signal power, not only in downlink but also in uplink dynamic channels, between an access point mounted on the wrist and a sensor module attached to various locations on a human body. The proposed antenna is comprised of two orthogonal antennas, which can obtain the optimum transmitting and receiving signals in considerations of the cross polarization power ratio (XPR) and antenna tilt angle. A dynamic channel model to represent the geometrical relationship between two locations considering arm-swinging motion was proposed.

Based on the model, a weight function was derived to control an orthogonal active antenna in an adaptive way for increasing the radiation pattern in the direction of a desired signal. Furthermore, a preliminary experiment using a 2-element polarization-controlled active antenna based on the proposed weight function has been carried out in an anechoic chamber. The results show that a high level of the received signal power can be obtained regardless of the arm-swing angle and antenna placement both in the measured data and analytical results, confirming the effectiveness of the proposed method to enhance the BAN on-body radio links has been confirmed.