# Design of MIMO Antenna with Double L-Shaped Structure for 5G NR
###### Abstract  
To satisfy the demand for 5G communication to smartphone terminal antennas in element quantity and isolation, an eight-element wideband MIMO antenna set of high isolation level is proposed. Each antenna element in the array is a double-L antenna consisting of an L-shaped slot and an L-shaped 50 \(\Omega\) microstrip line. The L slot is formed by adding an I-shaped open circuit directly to the side of the rectangular slot. In addition, the antenna arrays are located on the long bezels on both sides of the mobile phone motherboard, and the coupling feed is made in the frequency range of 3.6-4.7 GHz through the L-shaped microstrip line, so as to cover the 5G NR band (N77/N78/N79). Finally, the four element pairs (8 components) achieve isolation of greater than 11 dB, the performance frequency range is 3.6-4.7 GHz, the return loss is \(-6\) dB, the total efficiency is greater than 85%, and the envelope correlation coefficient is less than 0.08. Other MIMO performances are also calculated, the design process is discussed in detail, and one-handed grip mode and two-handed grip mode are discussed to demonstrate their stabilities in real-world applications.  
5G smartphones; slot antenna; MIMO antenna; sub-6 GHz band Article Design of MIMO Antenna with Double L-Shaped Structure for 5G NR Zhonggen  
signal, and in MIMO systems, the multipath effect of the wireless communication system is used to increase the channel capacity, so that the transmission rate of the antenna can be improved. In addition, slot antennas, which are widely used in communication, need to be slit in the conductor surface because they have a low figure of merit and wide impedance bandwidth, and this paper is based on slot antennas.  
Recently, several studies on MIMO antennas utilized in 5G NR (New Radio) operation bands have been done [3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24]. These studies proposed a number of antenna design methods, including the planar inverted-F antenna (PIFA), loop, monopole antenna, and inverted-F. In [2], we examined the two-antenna building block design consisting of a gap-coupled loop antenna and a loop antenna to improve isolation. The complex electromagnet environment made it such that the stronger the mutual coupling between the antennas, the greater the correlation and the worse the antenna radiation performance [25; 26]. Therefore, under the premise of ensuring a good antenna radiation performance, decoupling of multi-band antenna arrays and antenna miniaturization to improve the compatibility with smartphones have become the next problems to be solved.  
In view of the above discussion, this paper proposes a broadband eight-port slot antenna with high isolation suitable for 5G NR. Briefly, the antennas are designed using the approach of slotting the metal plate. In order to achieve broadband coverage with the impedance matching characteristics of the antenna, an open branch is added to one side of the rectangular slot to form an L-shaped slot. Furthermore, the L-shaped branch covering the 5G NR bands employs a coupled feeding scheme. The improved slot antenna has an ECC of less than 0.08 and a bandwidth of 3.6 GHz to 4.7 GHz.  
The remainder of this paper is structured as follows. Section 2 discusses the design process and working mechanism of the MIMO system. In Section 3, the fabrication of the proposed MIMO antenna system and the corresponding simulated and measured performance results are presented. A comparison table is also included to highlight the advantages of the suggested design. Antenna performance in hand-held situations, including single-handset mode (SHM) and dual-handset mode (DHM), is covered in Section 4. Finally, Section 5 draws conclusions about this paper.