Dual-wideband MIMO antenna for long term evolution and wireless local area network indoor applications

Abstract

Multiple-input multiple-output (MIMO) technique use multiple antennas at both transmitter and receiver to improve the performance of wireless communications system over multipath fading channels. A compact dual-wideband MIMO antenna with a size of 36 × 22 mm2 was proposed for indoor portable wireless systems to serve the LTE and WLAN applications, which cannot operate with the compact UWB MIMO antenna. Due to the UWB technology unable of covering the LTE 2500 (2.5-2.7 GHz) standard, and the UWB frequency range overlaps with the IEEE 802.11a standard for wireless local area networks (WLANs). The proposed dual-wideband MIMO antenna consists of two identical monopole antenna elements (MA) and microstrip feed line for each, which are placed on one side of the substrate. The ground plane with T-shaped stub is placed on the other side of the substrate to reduce mutual coupling and enhance the isolation between the antenna elements. The proposed antenna provides two operating bands of 2.5- 2.85 GHz and 4.85- 6.1 GHz are centered at 2.64 and 5.3 GHz respectively, by using the technique of strips and slits on the upper edge of the ground plane. The compact UWB MIMO antenna has a size of 32 × 20 mm2 also consists of two symmetrical MA elements and a ground plane with partial slope including protruding stub for isolation improvement and covers band of 3-11.52 GHz. To design and optimize the performance of the two proposed MIMO antennas, CST simulation software used to achieve the reliable results in term of S-parameters (reflection coefficient with mutual coupling between the two ports), and (radiation pattern with correlation coefficient) in term of diversity pattern. The two MIMO antennas were fabricated and tested, and there was a strong correlation between simulated and measured results of antennas indoor applications parameters such as return loss, VSWR, and radiation patterns. Therefore, the obtained results show that the two proposed MIMO antennas can operate with good 2:1 VSWR impedance bandwidth, good isolation better than 18 dB between antennas elements, envelope correlation coefficient (ECC) about 0.05 across desired bands, and diversity gain (DG) of 9.992 dB. Measurement results agree well with simulation results making these antennas suitable for portable applications.