A compact 4-channel microstrip MIMO antenna with reduced mutual coupling

A compact 4-channel multiple-input–multiple-output (MIMO) microstrip antenna integrated with inverted U-shaped microstrip resonators and line resonators is presented at 5.25 GHz frequency band (WLAN band). Microstrip resonators have been introduced for reduction of mutual coupling between the closely spaced antenna elements. A distance of 0.5λ is kept between adjacent patch elements, in order to achieve compactness of the MIMO structure. The simulation results show that the introduction of resonators of electrical length 2λg (λg = guided wave length) between antenna elements leads to suppression of mutual coupling by 44 dB at resonance frequency between the horizontal antenna elements. If line resonators of optimized length 22.1 mm (0.8λg) are introduced, then each of them suppresses the mutual coupling between the vertical elements by more than 35 dB at resonance. The length, width and distance between two arms of the inverted U-shaped resonator have been optimized to achieve minimum mutual coupling. The antenna with a compact structure based on the design has a peak gain of 10.54 dBi and a band width of 250 MHz. The antennas have been fabricated, measured and a good agreement between simulation and measured results are observed.