Isolation enhancement for four‐element MIMO antenna by using novel meandering technique

Abstract

The paper proposes a four‐element printed multiple‐input‐multiple‐output (MIMO) antenna with high isolation achieved by employing a compact decoupling method. The optimal shaping (meandering) of the monopole strip is adopted to realize decoupling at the working frequency band ranging from 5.004 to 5.320 GHz. The ports isolation S 21 ${S}_{21}$ and S 41 ${S}_{41}$ are improved by using self‐meandering technology with transmission zero occurring at the frequencies of 5.004 and 5.320 GHz, respectively. Meanwhile, the isolation S 31 ${S}_{31}$ is also greatly increased. The decoupling technique can significantly improve the isolations between the four ports of the proposed antenna, without the extra‐added structure. A four‐element MIMO antenna with an edge‐to‐edge spacing of 0.069 λ 0 ${\lambda }_{0}$ ( λ 0 ${\lambda }_{0}$ is the wavelength at 5.162 GHz in free space) is fabricated and measured. In the experiment, the proposed MIMO antenna has a relative bandwidth (reflection coefficient of −10 dB) of 6.12% with a range from 5.004 to 5.32 GHz. In addition, this design can significantly obtain higher port isolation, antenna efficiency, gain, and a lower envelope correlation coefficient (ECC).

A compact, high isolation building block for 8 × 8 multi‐input multi‐output antenna array suitable for 5G smartphone applications

“…In recent years, many MIMO antenna systems have been reported for mobile communications with acceptable isolation and envelope correlation coefficient (ECC) 6–26 . There are numerous mature decoupling methods available, including the use neutralization line (NL) method, 6–8 defected ground structure (DGS) method, 9–11 polarization diversity technique, 12–19 self‐decoupling, 20,22 using decoupling network, 24,25 and characteristic mode analysis 26 .…”

“…In recent years, many MIMO antenna systems have been reported for mobile communications with acceptable isolation and envelope correlation coefficient (ECC) 6–26 . There are numerous mature decoupling methods available, including the use neutralization line (NL) method, 6–8 defected ground structure (DGS) method, 9–11 polarization diversity technique, 12–19 self‐decoupling, 20,22 using decoupling network, 24,25 and characteristic mode analysis 26 . To validate the NL concept, a vertical metallic patch is added to the antenna, which can effectively suppress the ground plane fringing current as reported in Liu et al 6 To reduce coupling between the designed monopole antenna pair, a 3 mm NL is incorporated between antenna pairs, as reported in Shi et al 7 In Guo et al, 8 a NL helps to reduce mutual coupling between folded monopole antenna and a gap‐coupled loop branch.…”

“…However, more than 11 dB of isolation is achieved in Chen et al 24 with the help of an additional S ‐shaped decoupling network incorporated behind the resonating elements. In Wu et al, 25 isolation is improved with the help of a self‐meandering technology among the ports of four‐ the element MIMO array. Furthermore, a characteristic mode can create good isolation as reported in Qu et al, 26 however manipulating the frequency of various characteristic modes is difficult due to the limited freedom of adjusting the radiator, that is, the chassis.…”