Ultra-Compact Three-Port MIMO Antenna With High Isolation and Directional Radiation Patterns

In this letter, a disk-shaped ultra-compact three-port planar multiple-input-multiple-output (MIMO) antenna is proposed and fabricated. The antenna is designed for the 2.4-GHz WLAN band, the radius of which is only 16 mm ( 0.13λ). Three microstrip-fed T-shaped open-ended slots are used as radiating elements, whose edge-to-edge separation is only 0.006λ. They are rotationally symmetric and generate directional patterns that aim at 0^°, 120^°, and 240^°, respectively. The peak gain of these patterns is 2.3 dBi, and the pattern correlation coefficient is below 0.03, which provides good pattern diversity for an MIMO system. Meanwhile, the 3-dB beamwidth of these patterns is 105 ^°, which can realize nearly full azimuth coverage with its three beams. By introducing a newly designed neutralization network, the isolation between elements reaches 24 dB at the resonant frequency. Moreover, the proposed antenna is manufactured on the FR-4 substrate, which is cost-effective and easy to be implemented in a size-limited MIMO application.