# A High-Gain and Wideband MIMO Antenna for 5G mm-Wave-Based IoT Communication Networks
## 1 Introduction  
The increase in annual data use by 40 to 70% has strained capacity requirements, representing an increase by 1000 times with the passage of time. Considering progressing data needs, 5G is a competent candidate adept to offer a data rate of multiple gigabits per second [1, 2, 3]. To accomplish the required goals, experts have focused on the mostly unoccupied portion of the spectrum, i.e., mm-wave, where high bandwidth achievement is possible, due in part to the limited bandwidth and capacity constraints of the lower portion of the spectrum (sub 6 GHz) [4, 5]. Transmission based on 5G technology is not only intended to have high data rates and high quality of service but also to strengthen abilities of developing technologies, such as the Internet of Vehicles, virtual reality, smart cities etc. [6, 7]. Frequency bands for communication networks must be carefully allocated, as several challenges arise with a particular band selection [8], which is why several frequency bands are being considered by various telecom regulatory bodies and various countries. Most of the bands that have been allocated for 5G communication are within the ranges of 24-28 GHz, 37-40 GHz, etc. [9]. However, path loss and atmospheric attenuations factors must be considered and solved before considering transmission at these frequencybands [10]. Furthermore, the bandwidth should be wide enough to offer significantly high data rates [11]. Thus, the role of antennas is key in this regard, and they must be carefully designed to realize 5G communication systems and to effectively benefit users [12]. 5G systems will likely be built based on the multiantenna concept on both the transmission and receiver sides, making multiple input, multiple output (MIMO) configurations and also arrays are important in this regard [13]. To tackle attenuation-related issues in the case of mm-wave antennas, arrays are usually utilized to offer a narrow-beam radiation pattern [14]. However, these type of structures are focused on a single feed, and complex and simple power dividers are usually involved [15]. Controlling the losses in these type of power dividers is a challenging task, whereas a single feed results in limited capacity. Accommodating multiple antennas in an array structure to increase the gain also causes an increase in the profile [16]. Likewise, antennas incorporating lenses, metamaterials, and cavities are usually helpful to achieve high gain, and some antennas can maintain a low profile instead of high gain. For example, in [17], a DRA was developed with an EBG placed at a distance of 2.6 mm. The performance of the DRA was evaluated with and without an EBG. Overall, a 3 dB improvement in the gain was achieved. The size of the ground plane was 30 mm \(\times\) 30 mm for the 60 GHz band. In [18], an EBG ground plane and a dielectric superstrate were utilized to improve the gain of the antenna, resulting in a gain of more than 16 dB. The superstrate was placed 5.35 mm above the main antenna array with a complex power divider. The array structure resulted in a larger PCB size, as a 12 mm separation was used between the antenna elements. A 28 GHz operating frequency antenna was proposed in [19], with a peak gain of 15.6 dB. A fractional bandwidth in the range of 26.5-29.4 GHz was attained. A 3D-printed dielectric lens was utilized to attain high gain. Moreover, 50 mm \(\times\) 50 mm samples of polylactic acid (PLA) were fabricated. A complex structure was implemented in the proposed method to achieve high gain. However, the MIMO characteristic was lacking in the proposed designs, so capacity issues remained a challenge. Moreover, some of the proposed antennas lack a wide bandwidth. Recently, metamaterials with and without a combination of MIMO have been proposed. Antenna gain was improved by utilizing a three-pair metamaterial arrays in [20]. An overall gain of 7.4 dB was achieved, with bandwidth covering the range from 24.25 to 27.5 GHz and an overall size of 30.5 mm \(\times\) 30 mm.