Abstract
Ultra wide band - Multiple Input Multiple Output antenna technology provides higher data rates and the combination of the ultra wide band (UWB) and the multiple input multiple output (MIMO) technologies provides a solution for the demand of still higher data rates i.e. in excess of 3 Gb/sec in the future. As the antenna technologies are improving, the size of the MIMO antenna is growing smaller and smaller. Placing the antenna elements in such close proximity increases the coupling between them. Various isolation techniques have to be introduced between the antenna elements to decrease the coupling and to improve the isolation. A study of the various isolation enhancement techniques have been made in this review. It analyses the various isolation enhancement methods such as using orthogonal polarization, parasitic elements, varied decoupling structures, defected ground structures (DGS), neutralization line (NL) and finally by using metamaterials. Metamaterials is a technology to perk up the isolation between the antenna elements. Split ring resonator (SRR) behaves as a metamaterial and it is used as an isolation mechanism in this study. The antennas are simulated and the results are compared. The method using parasitic elements gives the highest isolation of 35 dB and it is 5 dB better than the methods using orthogonal polarization and using the decoupling structure. The performance of all the antennas satisfies the conditions for minimum isolation. The envelope correlation coefficient is nearly zero in all the antennas and it implies good diversity performance. The diversity gain is also calculated for the various antennas and it satisfies good diversity performance. The bandwidth of the antennas is in the UWB frequency range and they have a fractional bandwidth above the required value of 1.09. The capacity loss for all the antennas is very low and the antennas using defected ground structure and the decoupling structure gives very low capacity loss.
Highlights
As the quantity of applications and the number of users utilizing wireless communications is expanding, thereby the amount of data rate used is dynamically expanding
Data rates of more than 50 Mb/sec, multiple input multiple output (MIMO) and OFDM technologies are embraced as recommended in IEEE 802.11n
The matching conditions of the even-odd modes are dealt with independently in the proposed decoupling network. This helps in achieving high isolation and good impedance matching for the MIMO antenna
Summary
As the quantity of applications and the number of users utilizing wireless communications is expanding, thereby the amount of data rate used is dynamically expanding. To achieve the objective of 1 Gb/sec, advanced techniques such as UWB combined with MIMO provides the solution [1,2]. For the future technologies such as IEEE 802.15.3c wireless personal area networks (WPANs) utilizing a data rate of over 2 Gb/sec and for data rates in excess of 3 Gb/sec, the combination of MIMO and UWB technologies provides the necessary solution. High data rate communications are possible using UWB and it provides an excellent technology for short-range wireless communications. Without consuming extra radio frequency, MIMO technology provides higher data throughput along with an increase in range and reliability by exploiting multipath. An efficient antenna having these characteristics should be designed in the limited area provided
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