Tri-Band Four-Element Mimo Antenna With High Isolation

Abstract

A tri-band four-element MIMO (multiple-input-multipleoutput) antenna with high isolation is presented. The MIMO antenna consists of four symmetrical antenna elements. To relieve the degradation of the operation bandwidth caused by the strong mutual coupling among the four antenna elements, four symmetrical rectangles are removed from the four corners of the ground plane, respectively. The effect of the cutting of the four rectangles on the isolation is slight. Two kinds of isolation structure are applied to reduce the mutual coupling among the elements. The first kind of isolation consists of two slits and a protruded ground branch, and the second kind of isolation structure consists of four symmetrical slits etched into the ground plane. The mutual coupling caused by surface currents is reduced by slits, the mutual coupling resulted from near-field is suppressed by the ground branches, and thus high isolation for the MIMO antenna is achieved. Moreover, the effects of the slits and the ground branches on the operation bandwidth are slight, thus the operation bandwidth and the mutual coupling can be controlled independently, to some degree. A tri-band operation bandwidth (2.34-2.95 GHz, 3.38-3.75 GHz, and 4.4-6.7 GHz) with VSWR ≤ 2 and isolation ≥ 20 dB, is achieved. The results, including S-parameters, radiation patterns, mean effective gain (MEG), radiation efficiency and signal correlations, indicate that the proposed MIMO antenna can provide spatial or pattern diversity to increase data capacity of wireless communication systems.

General Decoupling Network Design Between Two Coupled Antennas for Mimo Applications

“…Inserting slits into the ground plane between the antennas can reduce the mutual coupling between antenna ports by suppressing surface waves between them [15][16][17]. Also, external decoupling structures are also presented through literature to eliminate nearfield coupling between antennas.…”

A novel eight ports dual band antenna array for 2.4/3.5 GHz MIMO applications

“…It is a critical problem for a MIMO system because it deteriorates the performance of MIMO system including the capacity [25][26][27]. Various methods have been used to reduce the coupling between the antennas [28], such as decoupling network, inductor coil, ground branches, electromagnetic band-gap (EBG) structure and an inverted-Y shaped stub inserted on the ground plane for two-element MIMO antennas. For four-element MIMO antennas, a series of slits etched into the ground plane, antennas placed uniquely and orthogonal arrangement of antennas were introduced.…”

Design of compact multiband pattern diversity antenna for WiMax, LTE and WLAN applications

“…Increased spacing between the ports to reduce mutual coupling will increase the size of the MIMO antenna. Use of effective isolation techniques to reduce the mutual coupling has been published in open literature including an isolation element separating two identical folded antenna modules (Chen et al 2012), use of a slotted complementary split ring resonator (CSRR) between the antennas inserted in the ground plane (Yang et al 2014), T-shaped junction on the top surface of the substrate and etching slots in the ground plane (Qin and Liu 2014), neutralization line (See et al 2012), slits etched in the ground plane (Li et al 2011;Cui et al 2011), inverted-L-shaped ground plane (Xiong and Gao 2012;Ding et al 2007). Table 1 gives the comparison of the sizes of various multiband papers.…”