A multi-input multi-output (MIMO) antenna for wireless local area network (WLAN) applications operating in 2.4 GHz and 5.8 GHz frequency bands is proposed in this paper. The proposed dual-band MIMO antenna is composed of two symmetrical radiation elements, and the isolation performance is improved by adopting parasitic elements and a defective ground plane. The measured reflection coefficients are less than −10 dB in the bandwidth range of 2.12–2.8 GHz and 4.95–6.65 GHz, respectively. The measurements show excellent isolation of −21 dB and −15 dB in both desired frequency bands, respectively. The total peak gain is greater than 4.8 dBi. The calculated envelope correlation coefficients (ECC), based on the measured S-parameters, are smaller than 0.01 and 0.024 in the lower and higher frequency bands, respectively. The dimension of the presented antenna occupies 50 × 40 × 1.59 mm³. It is suitable for IEEE 802.11 a/b/g/n (2.4–2.4835 GHz, 5.15–5.35 GHz and 5.725–5.85 GHz) WLAN applications.

A two-port multiple-input and multiple-output (MIMO) antenna with dual-band characteristics operating at the fifth-generation (5G) new radio (NR) sub-6 GHz n7/n38/n41/n79 bands is proposed. The proposed MIMO antenna is composed of two symmetric antenna elements and a defected ground plane. The antenna element consists of an incomplete circular patch with two L-shaped branches. By applying the defected ground structure and the slotted stub, the current distribution on the ground plane is changed to reduce the mutual coupling between the antenna elements. The measured −10 dB reflection coefficients cover 2.34–2.71 GHz and 3.72–5.10 GHz, while the measured isolation is larger than 20 dB at the whole operating frequency band. The paper has investigated different performance parameters in terms of the envelope correction coefficient (ECC), diversity gain (DG), radiation patterns, antenna gain, and efficiency. The proposed MIMO antenna is suitable for 5G applications.

A wideband multiple-input multiple-output (MIMO) antenna with high isolation for fifth-generation (5G) new-radio (NR) smartphone employment operating at a range from 3.3–5 GHz is presented in the paper. The wideband antenna is comprised of eight identical radiation units and applies defected ground structure (DGS) to offer higher isolation between antenna units. Each of the antenna elements is formed of a C-shaped microstrip line, two triangle-shaped strips and a rectangular strip. The measurement results present that the transmission coefficients of the presented antenna are smaller than −18 dB in the required wideband, and the envelope correlation coefficient (ECC) values are better than 0.005. The realized gain and efficiency of the designed antenna are about 3.5 dBi and higher than 75%, respectively. The volume of this total antenna is 150 × 75 × 7 mm³, and the measurement of each antenna unit is merely 6.8 mm × 7 mm × 0.8 mm ($0.077 \lambda \times 0.08 \lambda \times 0.009 \lambda$, $\lambda$ is the wavelength of 3.4 GHz). The presented MIMO antenna is suitable for 5G new-radio (NR) smartphone applications.

This article reported a compact ultra-thin tightly arranged 4 × 4 multiple-input multiple-output (MIMO) antenna pair (AP) functioning in the fifth-generation (5G) n78 band (3.4–3.6 GHz) for the ultra-thin 5G mobile handset. Two APs were printed on the center of two sideboards. A T-shaped open-ended slot was utilized in the grounding plane to improve the port impedance matching and attenuate the reciprocal magnetic coupling. A minimized total volume of 145 × 75 × 5 mm³ was obtained, and the area of each radiating unit was only 8.5 × 4.2 mm² (0.1λ₀ × 0.05λ₀, λ₀ is the free-space wavelength at the frequency of 3.5 GHz). By placing two radiating elements in an exceeding closed (1 mm or 0.01167λ₀) distance, the designed AP precisely resonated at 3.5 GHz, and an acceptable measured isolation performance superior to 17 dB was attained. A prototype of this presented APs system was printed and tested, and remarkable consistency was observed between the simulated and measured curves. Numerous indicators were computed to assess its MIMO performance, such as Envelope Correlation Efficiency (ECC), Diversity Gain (DG), Total Active Reflection Coefficient (TARC), and Multiplexing Efficiency (ME).