Design and verification of a dual‐band wearable antenna based on characteristic mode theory

Abstract

In this article, a novel design method is proposed based on characteristic mode theory (CMT). Based on the proposed method, a linearly polarised dual‐band wearable antenna with double‐layered substrates sandwiched by three layers of copper circle patches is designed and optimised step by step. The structure and excitation position of the antenna are obtained by progressively tailoring a classical circle patch antenna. Firstly, the characteristic mode analysis is performed on the middle‐layer planar circle patch to find the modes that can be excited in the designed frequency band. Secondly, the configuration of the middle layer is adjusted step by step based on the modal current distributions to realise the mode shift. Then, the top circle patch is changed to a metasurface to increase the number of modes and expand the mode bandwidth. Finally, the location of the excitation port is selected based on the modal electric fields to successfully obtain the desired performance of the antenna. The prototype of the proposed antenna with a radius of 2.6 cm fed by a single probe is fabricated and experimentally verified. The antenna operates in the 2.45 and 5 GHz bands, and the measured 10 dB impedance bandwidths on the two bands are 1.2% and 39.7%, respectively, which agrees well with the expectation predicted by the CMT. It should be noted that the desired antenna performance is achieved by step‐by‐step derivation using the CMT, rather than applying the theory to illustrate the working principle of antennas. The proposed design method can be broadly employed to various antenna designs.