# Design, Challenges and Developments for 5G Massive MIMO Antenna Systems at Sub 6-GHz Band: A Review
## 3 5G Antennas as a Candidate for Massive MIMO Technique at Sub-6 GHz
### Sub-Arrays
#### 3.2.2 Non-Symmetric Array
A good agreement was obtained between the measurements and simulations. These configurations were designed to cover the frequency range of 3.4 GHz to 3.8 GHz and showed a highly satisfactory performance exceeding \(-\)30 dB, while reducing the mutual coupling between the antennas that make up the system. The MIMO parameters of diversity such as ECC, diversity gain (DG), and overall performance were also investigated for every one of the proposed MIMO systems. Therefore, the results showed that the proposed two antenna configurations are quite suitable for 5G MIMO applications [112]. The triple band MIMO antenna for the 5G mobile terminal applications consists of 4-ports/2-resonators, each with a ground plane that is (50 mm \(\times\) 50 mm) in size and two concentric circular slot ring radiators engraved into it. A 50 \(\Omega\) microstrip line perpendicular feeds the antenna to the top layer. Decoupling methods have been utilized in order to suppress mutual coupling between two resonators. The vertical arrangement of leads and terminals reduces the mutual coupling between the two terminals and increases isolation. The antennas operate in multiple frequency bands (3.35-3.69 GHz, 24-28 GHz, and 37-40 GHz) and frequency ranges, with a focus on 3.5 GHz, 26 GHz, and 38 GHz-like assignments for 5G. The antenna provided a 2.7-7.8 dB gain and 0.49-0.85 radiation efficiency in the operating frequency band and the diversity performance in terms of ECC, diversity gain (DG), and TARC were checked. These were found to be \(<\)0.01, \(>\)9.99 dB, and less than \(-\)10 dB, respectively. The suggested antenna has excellent S-parameters, a low ECC, a decent VSWR, a TARC, a good radiation pattern, and a high gain. The production and testing of antennas. Results from the simulation and measurements were in good agreement. Applications for 5G mobile terminals and smart wearables have a lot of potential [113]. A novel dual-polarized, printed-dipole antenna design was proposed for base station antennas for 5G mobile communication systems operating in the 3.30-5.90 GHz band. Each crossed dipole was excited by a micro-tip wire stub fed from a standard 50 \(\Omega\) of coaxial cable. A configuration of synthetic dipole arms using third-order Bezier curves. This method provides precise tuning of the mutual coupling of the crossed dipoles and extension of the antenna's operating frequency band. The significant improvement in antenna performance compared to known prototypes was achieved after numerical full-wave optimization of the dipole profile. The characteristics of the proposed 8-element antenna array with improved planar dipoles were investigated. In the 3.30-5.90 GHz (57%) frequency band, the reflection coefficient was \(-\)15 dB, the isolation was \(-\)28, \(-\)30 dB, and the beam width of the \(-\)10 dB level corresponded to 120\({}^{\circ}\)\(-\)4\({}^{\circ}\)/+10\({}^{\circ}\)[114]. 4G/5G and combined (sub-6 GHz/mm-Wave) multi-band mMIMO can assist in solving more problems of 5G system structure such as bandwidth shortage and complex hardware requirements. The quality of the 5G antenna performance depends on the parameter chosen, the results of antenna work such as gain, power consumption, efficiency, bandwidth, and the surrounding environments of the antennas for the base station and smartphones. For instance, enhancement in the impedance bandwidth and gain in mMIMO will provide the maximum coverage area for the base station and smartphones. High channel capacity will offer high throughput and spectral efficiency. The diversity of pattern characteristics (gain, polarization) makes massive MIMO a good choice for 5G applications. Table 5 summarizes the types of 5G antennas (single and sub-array elements) as candidates for massive MIMO applications. These models are used depending on which is the most suitable for design in base station or smartphone applications. Many smartphone techniques use 2D model single and symmetric subarray elements.