Broadband High-isolation MIMO Antenna for 5G Smartphone Application
A compact broadband high-isolation Multiple-Input Multiple-Output(MIMO)antenna pair is proposed for 5G smartphones.By symmetrically placed the antenna pairs on the inner surface of both side frames,an 8-element MIMO array with low correlation is designed.A compact antenna pair is suggested based on a broadband coupling fed inverted-F antenna(IFA)arranged in null-space mirror symmetry.The-6 dB impedance bandwidth of antenna pair is 3.3～6.5 GHz(65.3%),which covers the 5G bands of n77/n78/n79 and LTE band 46.The size of antenna pair is only 26.8 mm×6 mm(0.29λ0×0.07λ0,λ0 is the free space wavelength of 3.3 GHz).By using the differential/common mode cancellation theory and loading distributed capacitors,the isolation between the two ports of the antenna pair is greatly improved.The isolation in the whole band is higher than 11 dB.Within the n79/LTE band46(4.4～5.925 GHz),the isolation is higher than15 dB with the peak isolation of 40 dB at the center frequency point of 4.9 GHz.The total efficiency is59%～88.8%within the whole band.To improve the isolation of the8-element MIMO array,a rectangular defective ground structure is etched between two adjacent antenna pairs.The Envelope Correlation Coefficient(ECC)are less than 0.1.A prototype of the proposed MIMO array is fabricated and measured,and the measured and simulated results agree well.
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