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 (0.13 lambda). Three microstrip-fed T-shaped open-ended slots are used as radiating elements, whose edge-to-edge separation is only 0.006 lambda. They are rotationally symmetric and generate directional patterns that aim at 0 degrees, 120 degrees, and 240 degrees, 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.