Design of a Dynamic Decoupling Network for a Pair of Wearable Inverted L-Shaped Antennas Based on Common/Differential Mode Theory

A design approach of a dynamic decoupling network (DDN) for wearable antennas is proposed in this communication based on common mode (CM)/differential mode (DM) theory. A pair of inverted L-shaped antennas (ILAs) is illustrated to verify the design idea and method. First, the ILAs with matching network are designed on a handheld terminal, and the decoupling network is realized by a horizontal strip and a lumped capacitance inserted between the antenna pair, which is based on the CM/DM theory. Then, we discuss the influence of the human body on the antenna performances and show that the DM is more affected by the human body than the CM. Next, a varactor diode is employed to dynamically adjust the DM impedance, which can guarantee that the antennas have good impedance matching and isolation in both scenarios in free space and on human body. Finally, to verify the feasibility of the proposed method, the proposed antenna pair with the decoupling network is fabricated and tested in free space and on human body, while the measured results agree well with our analyses. The proposed design approach shows considerable promise for the design of future multiple-inputmultiple-output (MIMO) antennas for wearable devices.