A 4x4 Planar UWB-MIMO Antenna with Dual Linear Polarization for WLAN/5G/WiFi/X-band Samuel de J´ esus Ndimubandi and Xiao Ding Institute of Applied Physics, University of Electronic Science and Technology of China, Chengdu, West Hi-Tech Zone 611731, China (sjndimubandi@std.uestc.edu.cn, xding@uestc.edu.cn) Abstract—This paper describes a 4 × 4 planar ultra-wideband multiple-input multiple-output (UWB-MIMO) antenna with a compact size of 29.28 mm × 29.28 mm × 1 mm. The an- tenna employs a defected ground structure-assisted bandwidth improvement approach for achieving ultra-wideband operating bandwidth. Within the frequency range of 4.7 to 22 GHz, the isolation level of the proposed antenna is less than 20.5 dB. The envelope correlation coefficient (ECC) is good enough, less than 0.0027 with the diversity gain (DG) being nearly 10. All scenarios were simulated using CST Studio 2020. The proposed antenna was manufactured and tested. The test and simulation results are in good agreement. I. I NTRODUCTION Today’s fifth-generation (5G) wireless communications are designed to fulfill the growing need for faster data speeds, more efficiency, and flexibility than fourth-generation (4G) wireless communications. Planar antennas are most used in UWB transceiver systems. As it is well known, the primary advantages of ultra-wideband wireless communication systems operating at frequencies ranging from 3.1 to 10.6 GHz are their high data rate [1], excellent ability to overcome multipath fading, and other characteristics. Research on UWB-MIMO antennas mainly focuses on compactness, bandwidth, high isolation, and band-notched properties. However, integrating multiple components within a limited area inside a communi- cation device/system is tricky [2,3]. A 60 × 35 mm 2 novel compact monopole UWB antenna using defect in ground plane (DGS) to reduce the mutual coupling operates from 2.0 to 10.0 GHz impedance bandwidth and produces the tri-band resonant frequencies between 3.0– 4.0 GHz (S 11 ≤-23.73 dB - S 21 ≤-16.53 dB), 4.3–5.6 GHz (S 11 ≤-27.43 dB - S 21 ≤-18.17 dB), and 8.4–9.5 GHz (S 11 ≤- 19.87 dB - S 21 ≤-17.95 dB) [4]. In [5], the isolation of more than -18 dB was achieved by introducing a hexagonal- shaped complementary split-ring resonator (HCSRR) in the radiators of a 58 × 58 × 0.8 mm 3 planar, microstrip line- fed, quad-port multiple-input multiple-output (MIMO) antenna in a frequency range of 3–16 GHz. In [6], the antenna’s notched bands of 3.25–3.75 GHz, 5.08–5.90 GHz, and 7.07– 7.95 GHz are well aligned with the current WiMAX (3.3– 3.7 GHz), WLAN (5.15–5.875 GHz), and X-band (7.1–7.9 GHz) interference bands. The isolation level is below -22 dB by using a four-directional staircase-shaped decoupling, numerous slit, and slot approaches. This paper proposed a 4 × 4 planar ultra-wideband multiple- input multiple-output (UWB-MIMO) antenna. The proposed antenna’s size is smaller than in [4], [5], and [6]. Due to the (a) (b) Fig. 1: Geometry of the proposed antenna: (a) Top view, (b) Bottom view. fact that the proposed antenna has up to four antenna elements and four data streams for each user or a mobile station, the proposed antenna also covers a broader bandwidth without notched bands. It provides better isolation for WLAN (4.9– 5.725 GHz), 5G (4.8–5.0 GHz), WiFi (5.15–5.85 GHz), and X-band (7.1–7.9 GHz) interference bands than [4] and [6]. Fig. 2: Current distribution of the design process of the single port antenna at 5.5 GHz: (a) Type I, (b) Type II, (c) Type III. II. STRUCTURE OF THE PROPOSED ANTENNA A planar rectangular monopole antenna powered by a 50Ω microstrip line is the basis for the proposed antenna. It is constructed on an FR4 substrate (4.4 of permittivity, 0.025 of loss tangent, and 1 mm of thickness). The UWB planar monopole antenna is designed using a triangular defected mi- crostrip structure and a staircase-shaped structure to improve the model’s radiation characteristics and compactness. A 1.5 × 2 mm 2 rectangular slit etched on the edge-cropped groove ground plane of 5 mm in length is created to boost the antenna’s bandwidth element. Fig. 1 shows the 4 × 4 planar ultra-wideband multiple-input multiple-output (UWB-MIMO) 946 978-1-6654-9658-2/22/$31.00 ©2022 IEEE APS 2022 2022 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting (AP-S/USNC-URSI) | 978-1-6654-9658-2/22/$31.00 ©2022 IEEE | DOI: 10.1109/AP-S/USNC-URSI47032.2022.9886922 Authorized licensed use limited to: University of Electronic Science and Tech of China. Downloaded on October 27,2022 at 18:23:59 UTC from IEEE Xplore. Restrictions apply.