In this communication, a metasurface-based decoupling method (MDM) is proposed to reduce the mutual couplings at two independent bands of two coupled MIMO antennas. The metasurface superstrate is composed of pairs of non-uniform cut wires with two different lengths. It is compact in size and effective in decoupling two nearby dual-band patch antennas that are strongly coupled in H-plane with the edge-to-edge spacing of only 0.008 wavelengths at low frequency band (LB). The antenna is fabricated and measured and the results show that the isolation between two dual-band antennas can be improved to more than 25 dB at both 2.5-2.7 GHz and 3.4-3.6 GHz bands while their reflection coefficients remain to be below -10 dB after the metasurface superstrate is introduced. Moreover, the total efficiency is improved by about 15% in the low band and the envelope correlation coefficient (ECC) between the two antennas is reduced from 0.46 to 0.08 at 2.6 GHz and 0.08 to 0.01 at 3.5 GHz. The proposed method can find plenty of applications in dual-band MIMO and 5G communication systems.

A ceramic superstrate-based decoupling method (CSDM) is proposed to reduce the mutual coupling between two closely packed dipole antennas while maintaining cross-polarization suppression. Compared with other superstrate-based methods, this proposed method can effectively reduce the mutual coupling between the antennas without using any periodic structures on the superstrate. The ceramic superstrate is a 2 mm thin slab with a relative dielectric constant of 20.5 and is suspended over the antennas coupled in H-plane with the spacing of only 0.28 wavelength at 3.5 GHz. It is demonstrated by both simulation and measurement that the isolation between two dipole antennas can be improved from 10 dB to more than 25 dB within the operation band while their reflection coefficients remain to be below -10 dB after the ceramic superstrate is introduced. The radiation patterns of the antenna maintain stable at different operation frequencies within the band of interest and the peak gain has increased by around 1.5 dB. Meanwhile, the total efficiency is enhanced by about 15% and the envelope correlation coefficient (ECC) between the two antennas is reduced from 0.7 to 0.4.

A miniaturized two-element microstrip antenna array is proposed for the millimeter wave band of 5-th Generation (5G) wireless communication systems. A surface of electromagnetic band gap structures (EBG) is applied as the ground for two closely packed patch antennas operating in 5G New Radio (NR) (26500 MHz - 29500 MHz) frequency band. With the help of the proposed EBG ground, the two E-shaped microstrip antenna elements can be placed in close proximity to each other by 0.3 wavelength center to center distance in free space at the center frequency, yet the mutual coupling between them can still reach to more than 23 dB within the whole band of interest, which is about 10 dB larger than that on normal ground. All major radiation characteristics of the two-element array are well reserved with the EBG ground. The proposed design can be used in multiple-input-multiple-output (MIMO) applications or as the building subarray of larger phased arrays at millimeter wave bands for mobile communication systems.

A compact circularly-polarized patch antenna with wide axial-ratio beamwidth (ARBW) operating at dual bands compatible for GPS satellite navigation application is proposed in this paper. The antenna consists of two stacked patches, which account for GPS L1 band (1575 ± 2 MHz) and L2 band (1228 ± 2 MHz). To realize significant size miniaturization, four pillars are introduced and strongly coupled to the lower patch. To adjust the beamwidth response of the far-field components, the antenna is backed by a modified metallic cavity, which in turn widen the 3-dB axial ratio beamwidth (ARBW) at two operating bands effectively Finally, the proposed design with excellent performance is realized in a size of 0.368 λ0 (diameter) and 0.105 λ0 (height). Simulated and measured results show that the ARBWs at L1 and L2 bands are as wide as 173° and 133°, respectively. For practical application, its satisfactory GPS signal receiving capability is also verified by outdoor positioning test.

In this paper, meta-surface superstrates are used to decouple two linear polarized antennas coupled in H-plane and E-plane, respectively. By properly designing the geometry of the double layer short wires as the unit cell of the meta-surface, as well as the height of the meta-superstrate, two linearly polarized antennas can be decoupled in H-plane and E-plane respectively. Both the antenna pairs coupled in E-and H-planes with and without meta-surfaces are fabricated and measured. Results demonstrate that the antennas with the meta-surface superstrate are able to operate in the band of 3.3 GHz to 3.7 GHz with reflection better than -15 dB and the isolation can be improved from 10 to 25 dB in the H-plane case and can be improved from 15 to 30 dB in the E-plane case. Such decoupling method can be applied extensively in 5G base stations where size constraints are becoming stringent.

A compact phased array with extended beam steering characteristics for the millimeter-waveband of the fifth-generation (5G) applications is presented in this communication. An E-shaped patch antenna placed on an electromagnetic bandgap ground (EBGG) with operating bandwidth of 24.2–27.5 GHz is used as the basic building block of the eight-element linear array. The array utilizes both the in-phase reflection characteristic for broad element radiation pattern and the bandgap characteristic for mutual coupling reduction for limited inter-element spacing of the proposed array. The existence of the EBGG enables a compact array with the inter-element spacing of around 0.4 wavelengths at the center frequency, yet the isolation between each element is still above 17 dB within the whole band of interest, which also helps to increase the array directivity at large scanning angles. The scanning angle of the array with the electromagnetic bandgap (EBG) structure ranges from −75° to 75° at 26 GHz within 3 dB scanning loss. The proposed EBGG extends the antenna array’s spatial coverage and enables a compact size of the array, which is very attractive for 5G millimeter-wave (mm-wave) application.