Systematic Design of a Multiport MIMO Antenna With Bilateral Symmetry Based on Characteristic Mode Analysis

There are various bilaterally symmetric structures in the world. Characteristic mode analysis (CMA) enables to use a conductor with the symmetric structure itself as an antenna. Based on CMA, it is possible to implement a multiport MIMO antenna on the conductor using a mode-decoupling network (MDN). As the number of antennas increases, however, the complexity of the MDN becomes large, making design difficult. In this paper, we propose a simpler systematic design method for a multiport MIMO antenna on an electrically small and bilaterally symmetric conductor. More specifically, the implementation of the MDN depends on the design of the coupling elements that excite characteristic modes, so a design method for its position and shape is proposed. Owing to the well-designed coupling elements, a simple systematic design of the multiport MIMO antenna is suggested. The proposed design method is verified by simulation and measurement of a bug-like 3-port MIMO antenna operating in the 2.4 GHz ISM band, applicable to biomimetic drones. The antenna is realized using an FR-4 substrate with dimensions of 50 mm <inline-formula> <tex-math notation="LaTeX">$\times \,\, 61.5$ </tex-math></inline-formula> mm <inline-formula> <tex-math notation="LaTeX">$\times \,\, 10$ </tex-math></inline-formula> mm (<inline-formula> <tex-math notation="LaTeX">$0.4\lambda _{0} \times 0.49\lambda _{0} \times 0.08\lambda _{0} $ </tex-math></inline-formula> at 2.4 GHz). The measurements demonstrate that these antennas have a low mutual coupling (<−20 dB) and a low envelope correlation coefficient (<0.04).