JultikaUniversity of Oulu repository

Nowadays, wireless device users engage in various forms of wireless applications and services. Multiple-Input Multiple-Output (MIMO) system technology, which involves multiple uses of antennas at both the transmitter and the receiver side of wireless channel, can be used to improve the wireless channel capacity without any need for extra spectrum in the rich scattering environment. The MIMO technology is regarded as a fundamental component for this new emerging wireless communication Long Term Evolution (LTE) standard. However, as a result of short distance between the antennas in the small mobile terminals, the total antenna efficiency gets reduced and the mutual coupling that exists between the MIMO antenna elements also becomes very high which lead to high Envelope Correlation Coefficient (ECC). This Master’s thesis aims to study the impact of antenna type on the ECC for a two antenna system in a typical mobile terminal sized device (ground plane) by using different configurations of antenna placement. The mobile antennas are to operate in LTE band 3 (from 1.710 GHz to 1.880 GHz) and LTE band 20 (from 0.791GHz to GHz 0.862 GHz). This thesis has been addressed by first introducing the fundamental theory of antennas. It is followed with description of effect on ground plane due to different mobile antenna structures and as a last part on the basics of LTE and LTE-Advanced components, focusing on the concept of multiple antennas design on mobile terminal. In this thesis, three types of antenna structures have been considered: Planar Inverted-F Antenna (PIFA), monopole and loop antennas. The designs and simulations of the antenna structures have been performed using CST Microwave studio software. The two antenna systems showed better performance when one antenna is located at the bottom of the ground plane with feed at the corner and the second antenna is placed perpendicularly at the top with feed positioned on the same side of the ground plane as the bottom antenna. ECC values of less than 0.2 in LTE band 3 and less than 0.49 in LTE band 20 were obtained. The study shows that good efficiency and low ECC (low mutual coupling) can be achieved from the placement of the MIMO antennas on the ground plane. In consideration to future work, the results in this thesis can serve as helpful information in multi-antenna designs for mobile terminals.