Contents I. Introduction
In the previous few years, a remarkably growth in mobile phone traffic has been identified with the ultimatum of higher data rate and bandwidth. So far, the current 4G technology has delivered sufficient data rate and bandwidth to cover today’s need of telecommunication sector. But it is estimated that data traffic from the wide-ranging social applications, smart cities, video streaming and cloud service will go beyond the capacities of the present 4G infrastructures through 2020 [1]. To overcome this problem, exploration has been started on the upcoming generation 5G of mobile communication. The 5G provides good services of higher data rates, wider bandwidth and larger number of frequency channel as likened to 4G. For achieving these 5G services mainly high data rates and bandwidth, we need to move towards the unused idle higher frequencies of centimeter and millimeter (3-300 GHz) in the electromagnetic spectrum [2]. But utilization of higher frequencies greater than 6 GHz causes an upsurge in free-space path loss problems because these larger frequencies are significantly affected by atmospheric attenuation [3]. Using narrow beam with high gain antenna in MIMO system scenario at both the sender and receiver side, we can achieve high data rates with reliability and can overcome the signal fading problems in 5G mm- wave applications [4]. Antenna research community has displayed more concentration to improve antenna design at 28 GHz, 38 GHz frequency bands because these two mostly concentrated bands for 5G communication have lowest atmospheric attenuation property. In [5] a MIMO antenna of four ports is presented covering the 28 GHz 5G frequency band having a peak gain of 5.5 dBi with pattern diversity characteristics due to its geometrical placement of radiating elements. However, to tackle the atmospheric attenuation problem this peak gain is insufficient at the desired band. A four-port infinity shell-shaped array is proposed in [6] with a peak gain of 7 dBi and ECC less than 0.15 over the desired operating bandwidth. But the peak gain achieved in this work is relatively small for the MIMO system. Similarly, in [7] a microstrip patch antenna with dual band operation at 28 and 38 GHz is presented. Although a satisfactory gain of 12.3 dBi is achieved at both of desired operating frequency bands, but it has a very narrow bandwidth of less the 1 GHz. In [8], a 1x4 vertical monopole array is presented to attain a broad beam coverage however, still the peak achieved gain is low. Furthermore, a four-port MIMO antenna using 1x2 array with defected ground structure is proposed in [9] where a wide bandwidth of 4.1 GHz is achieved with 8.3 dBi peak gain. In literature [11]-[14] various antenna designs have been presented for 5G communication in which most of the antennas are based on signal element while few of them are array-based with signal port. However, the multielement array antenna fed with a signal port exhibit the same capacity as the signal element antenna. Additional problem in these designs is that they are not in MIMO configuration due to which they are unsatisfactory to fulfill the requirements of high data rates demanding devices and throughput performances. On the other hand, MIMO antenna establishes multipath propagation with increased channel capacity, link reliability and high data rates which are the key descriptions of 5G.
