A Compact MIMO Antenna using CRLH Configuration Double-Layered Folded Ring Radiations with Planar Mushroom Decoupling Structure

This paper proposes a novel compact multiple-input-multiple-output (MIMO) antenna, which has miniaturized radiators and improved isolation, working for the long-term evolution (LTE) mobile communication. Each of the proposed radiators has a double-layered ring of the composite right- and left-handed transmission-line configuration, which has the footprint of λ_g/30 by λ_g/30, much smaller than the conventional MIMO antenna radiators. These radiators can be placed close to each other and have a planar modified mushroom structure between them for a higher isolation level. The design starts from the equivalent circuit for the LTE 1.7-GHz-band antenna, finds a physical structure suitable for the circuit, and is verified by comparing the circuit simulation with the 3-D EM simulation and measured data. The dispersion diagram shows that the zeroth-order resonance coincides with the center frequency of the band, and the fabricated antenna has the return loss less than -10 dB, the isolation over 12 dB, and the radiation efficiency over 50%.