Mutual Coupling Reduction of Rotationally Symmetric Multiport Antennas

A systematic method for reducing the mutual coupling of a rotationally symmetric multiport antenna system is proposed. A compact design example for a four-port antenna with low mutual coupling across two frequency bands centered around 2.4 and 5.8 GHz is provided. The entire size of the proposed four-port antenna is 0.28λo× 0.28λo× 0.04λo, where λois the wavelength in free space, and it is compact enough for the use in smartwatch applications for example. The defected ground structure and slot-lines used in the design are also modeled with an equivalent circuit to explain the achieved high port isolation. A prototype is fabricated and tested to confirm the results of the electromagnetic simulation. Furthermore, the proposed design method can be applied to five-port and three-port antenna systems in rotationally symmetric geometries for suppressing mutual coupling between ports.