# Design, Challenges and Developments for 5G Massive MIMO Antenna Systems at Sub 6-GHz Band: A Review
## 2 5G Massive MIMO at Sub-6 GHz
### 5G Massive MIMO Antennas for BS Applications
#### 2.1.1 2D Massive MIMO
Simulation tests show that the anticipated dual polarization 2-chamfered aerial bowtie dipole antenna has a SWR of 1.5 and bandwidths between 2.8 and 4.0 GHz, a \(-\)27 dB isolation between the two ports, a 9.1 dBi gain for both polarizations, and a mutual coupling of roughly \(-\)25 dB. The antenna features a simple, easily-manufacturable design with an overall height of 0.25\(\lambda_{0}\)[32; 33]. Based on patch antennas, a mMIMO antenna system design is described. Each port in the array has a (2 \(\times\) 2) patch antenna sub-array with a distinct phase excitation at every one of the elements to tilt the beam into a different direction and produce lower correlation coefficient values. The array has 16 ports (64 elements) in total. To deliver the beam-tilts, a fixed progressive phase feed network has been designed [34]. The antenna system uses a three-layer FR-4 substrate with a total size of 33.33 cm \(\times\) 33.33 cm \(\times\) 0.16 cm and is designed to operate at 3.6 GHz with a 230 MHz bandwidth, good isolation between the neighboring ports at a minimum of 25 dB, and achieved gains of 5.4 dB for each port [34]. For a sizable indoor MIMO base station, a portable ultra-wideband MEA was investigated. The antenna's design was based upon the simultaneous activation of several characteristic modes in every MEA element. Therefore, an (11 \(\times\) 11) mMIMO array with a size of 70 cm by 70 cm and 121 physical antenna elements could be used to construct an effective 484-port antenna, as can be seen in Figure 4. Compared to the standard cross-dipole MEA, this resulted in a 54% size decrease. The antenna has a reflection coefficient of \(<\)\(-\)10, an intra-element and inter-element interconnection of \(\leq\)\(-\)20 at the antenna port, and operates over a very broad frequency range of 6 to 8.5 GHz. It uses the 3D radiation patterns to calculate the total antenna efficiency, which is around 70% for all four ports [35; 36]. Figure 4: The prototype of an (11 \(\times\) 11) mMIMO array of multimode elements has 484 antenna ports [35]. Wider carrier bandwidth, native mMIMO, and minimal latency are features of a sample 5G air interface. It has been shown that all physical channels could be designed to function with small beams. Eight streams of 64 QAM can be sent simultaneously for a single UE with eight antennas, and 5 Gbps throughput is possible at 200 MHz. It is possible to obtain a 10 Gbps throughput for multiple UE through evenly distributing such UEs in an outdoor setting. Additionally, this system was created using a commercial LTE hardware and software platform, and our top priorities regarding engineering were size, cost, and the power consumption limits. mMIMO may thus be a workable solution for the 5G wireless system. Future tests will examine increased multiple UE throughputs, multiple cell handover, velocity robustness, and collaboration [37]. As BS antennas consist of mMIMO systems, new broadband partial ground plane microstrip antennas and microstrip planar arrays are being developed. For upcoming 5G networks, broadband antennas and planar arrays are being designed for sub-6 GHz bands. Compared with the millimeter frequency band, this band has better coverage. Line-of-sight issues and losses due to atmospheric attenuation affect this mm frequency. The Roger 3003 substrate was used to build the antenna. The substrate was 50 mm \(\times\) 50 mm \(\times\) 1.5 mm in size, whereas 16.3 mm was the partial ground plane length, and 0.035 mm was the thickness of the PCB's metal layer substrate. However, the size of the microstrip feed line had a length of 17 mm and width of 2.5 mm, respectively. The patch size was length 19.5 mm \(\times\) width 17 mm, and this design had inset 1 and inset 2, which had the same dimensions (length 3 mm \(\times\) width 0.5 mm) [38].