Research and Development on Information and Communication Technology Compact Wide-Band and Low Mutual Coupling MIMO Metamaterial Antenna using CPW Feeding for LTE/Wimax Applications Duong Thi Thanh Tu 1, 2 , Nguyen Tuan Ngoc 1 , Vu Van Yem 2 1 Faculty of Telecommunications 1, Posts and Telecommunications Institute of Technology, Hanoi, Vietnam 2 School of Electronics and Telecommunications, Hanoi University of Science and Technology, Hanoi, Vietnam Correspondence: Duong Thi Thanh Tu, tudtt@ptit.edu.vn Communication: received 12 May 2016, revised 23 January 2017, accepted 8 May 2017 Online early access: 8 November 2018, Digital Object Identifier: 10.32913/rd-ict.vol2.no15.676 The Area Editor coordinating the review of this article and deciding to accept it was Assoc. Prof. Nguyen Van Duc Abstract: In this paper, a metamaterial antenna is designed by using coplanar waveguide (CPW) feeding to obtain wide- band and compact size. The Multiple-Input Multiple-Output (MIMO) antenna is constructed by placing side-by-side two single metamaterial antennas which are based on the modified composite right/left handed (CRLH) model. The proposed antenna covers 22% of the experimental bandwidth for both cases of single and MIMO antennas. Implemented in FR4 substrate with the height of 1.6 mm, the antenna is compact in size with radiating patch dimension of 5.75 × 14 mm 2 at 3.5 GHz resonant frequency that is suitable for Long Term Evolution (LTE)/Wimax applications in handheld devices. Furthermore, the combination of Defected Ground Structure (DGS) and enlarged ground of coplanar structure has solved the challenge of mutual coupling between elements in the MIMO metamaterial antenna using CPW feeding. With the distance of 0.46λ 0 between feeding points, the MIMO antenna obtains the high isolation of under -20 dB for a huge bandwidth with a good agreement between simulations and measurements. Keywords: Multiple-input multiple-output (MIMO), metamate- rial antenna, coplanar waveguide (CPW), low mutual coupling, defected ground structure (DGS). I. I NTRODUCTION To satisfy high demands of users such as high data trans- fer rate and fast access, wireless communication technolo- gies have been developed rapidly in recent years. Among them is the MIMO technology which has been deployed in terminals of modern wireless communication systems such as: 802.11n, 802.11ac, 802.11ad, 802.16m, LTE, LTE- advanced, and 5G systems. The most significant feature of MIMO is a high increase in channel capacity without bandwidth addition or increase of transmission power [1]. However, MIMO antenna systems require high isolation between antenna elements and compact size to be applied for portable devices [2]. There are several techniques used to decrease the size of antennas, such as incorporating a shorting pin in a microstrip patch [3], using short-circuit [4], or cutting slots in radiating patch with the fractal configuration [5]. Although these methods have achieved quite impressive compact size, they face challenges in terms of efficiency and gain reduction. On the other hand, using metamate- rial is another method that provides an opportunity for designing small-dimension antennas with low cost and better performance parameters at both antenna and system levels [6, 7]. Besides, by using coplanar waveguide feeding, the metamaterial antenna is able to enlarge bandwidth [8]. Furthermore, coupling between microstrip antennas is important in a MIMO system. Mutual coupling between antenna elements is an unwanted phenomenon that distorts the behavior of the radiating elements. In MIMO systems, each antenna affects other elements that are closely packed by radiating over the air or by propagating surface cur- rents through the ground plane. Thus, the performance of antennas tends to drop, especially for MIMO metamaterial antennas. Many methods have been proposed to decrease mutual coupling between antenna elements, such as groov- ing dielectric, covering the patch by dielectric layers, or using shorting pins to cancel the capacitive polarization currents of the substrate. However, one technique widely used in antenna designs recently is using metamaterial structures such as DGS and Electromagnetic Band Gap 21