A coplanar waveguide (CPW) fed flexible interconnected 4-port MIMO antenna is proposed for UWB, X, and Ku band applications having a size $0.67\lambda \times 0.81\lambda \times 0.0028\lambda $ (at 3.58 GHz). The antenna parameters are characterized by using sets of real measurements to validate the antenna design and modelling. A precise milling machine is used for fabricating the single and 4-port antennas over a flexible FR-4 Substrate. Vector network analyser (VNA) is used for measuring scattering and transmission coefficients. As well as, a shielded anechoic chamber is utilised for measuring the far field radiations and the gain of the antenna under test (AUT). The basic antenna that is a part of the 4-port structure consists of a CPW fed octagonal structure surrounded by an octagonal-shaped slot. The MIMO ability is achieved by arranging the 4 identical elements symmetrically in a successive rotational means for achieving good polarization diversity. The connected ground between the elements is achieved by introducing a plus-shaped slotted structure separated by a slotted diamond at the center in the 4-port structure. None of the slots touches each other thus ensuring the common reference while maintaining the inter-element isolation better than 15 dB. The antenna demonstrated maximum gain and minimum efficiency of 6.8 dBi and 89%, respectively besides attaining a 10-dB impedance bandwidth of 125.83% (3.89-17.09 GHz) and envelope correlation coefficient (ECC) < 0.02. Finally, the 4-port flexible antenna is tested in terms of S parameters and ECC under bending conditions along the X and Y axis followed by a time-domain analysis that exhibited very good performance.

This letter presents a design of a two-element multiple-input-multiple-output (MIMO) metamaterial-based antenna. The two antenna elements operate at 5.8 GHz for wireless applications. The two antenna elements are designed employing only one left-handed unit cell. The reduction of mutual coupling between the two antenna elements is achieved by using a simple defected ground structure between them to limit the surface waves between them. The distance between the two antenna elements is only 1.8 mm (0.034 λ0). The designed antenna elements have better than -45 dB coupling isolation between the two inputs. Moreover, the proposed MIMO antenna has the advantage of compactness (its size is only 2.36 × 2.6 cm²). The design represents size reduction of more than 50% compared to conventional patch antennas operating at the same frequency. The proposed MIMO system has -55 dB correlation coefficient between its two elements.

This paper presents a dual-band 28/38 GHz two elements multiple-input multiple-output (MIMO) antenna with high isolation for 5G applications. The suggested antenna is a monopole with rectangular and triangle stubs added to the patch and a partial ground plane to achieve the dual band’s behavior. Two elements of the suggested antenna are combined and placed orthogonally to achieve the high isolation features of the MIMO configuration at 28/38 GHz. The MIMO configuration has a size of 27.65 $$\times$$× 12 $$\times$$× 0.273 mm³. The suggested MIMO prototype is fabricated and tested. The tested results achieved dual frequency bands with S₁₁ lower than − 10 dB within two frequency bands (26–30 GHz and 36–41.5 GHz) and S₂₁ lower than − 20 dB through the two operated bands. The suggested antenna has semi-omnidirectional radiation patterns in both planes. As well, its measured peak gain is 5.2 dBi and 5.3 dBi at the two operated frequency bands, respectively. Also, the MIMO parameters are extracted to validate the simulated results. The simulated and tested results have a good matching within the two operating bands which suggests the proposed structure be utilized in 5G communications.

In this paper, a 38 GHz 4-port multiple-input multiple-output (MIMO) antenna with considerable isolation and gain enhancement for 5G applications is introduced. The suggested antenna element is a monopole antenna composed of a circular patch with a rectangular slot etched from it and a partial ground plane is used to extend the desired frequency to operate from 36.6 GHz to 39.5 GHz with a center frequency of 38 GHz. The high isolation is achieved by arranging the four elements orthogonally and adding four stubs to reduce mutual coupling between elements at the desired frequency bands. The gain improvement is also introduced by placing a frequency selective structure (FSS) which is designed at the same frequency bands of the antenna under the suggested MIMO antenna to act as a reflector. The proposed four-element MIMO with the FSS prototype is built and tested in order to confirm the simulated results. The suggested antenna operated from 37.2 GHz to 39.2 GHz with an isolation of less than 25 dB across the obtained frequency range. The peak gain of the antenna is enhanced from 5.5 dBi to around 10 dBi by utilizing the FSS structure; furthermore, the back radiation is enhanced. The MIMO performance is validated by extracting its parameters and comparing with the simulated results. The results extracted from the simulation and the measurement show satisfactory matching along with the target band, indicating that the proposed structure could be used for 5G communications.