The Theory Of Characteristic Mode And Its Applications In The UWB MIMO Antenna

Theory of Characteristic Modes(TCM)has attracted plenty of attention in the field of antenna engineering in recent years.It can not only give the physical interpretation behind the key performances of an antenna,but also solve the electromagnetic problem of complex boundary and give a high precision solution.It processes the unsolved problem using the characteristic modes of the structure as the expanding functions,and becomes a popular approach to characterize the radiation mechanism of arbitrarily shaped objects.With the increasing demand for the communication rate and quality,how to improve the channel capacity and communication quality of wireless communication systems has become an important topic in the research of wireless communication technology.Ultra Wide Band(UWB)communication technology can make full use of spectrum resources,and has good security performance and high transmission efficiency,with a low power spectral density.Multiple Input Multiple Output(MIMO)technology has the advantages of high spectral efficiency,wide coverage,low power consumption,high link reliability,etc.UWB MIMO technology can effectively increase the channel capacity and operating band by combining the two technologies,which has broad application prospects in wireless communication systems.In this thesis,exploratory research on the TCM has been carried out and UWB MIMO antennas are designed and analyzed ulteriorly.Brief introduction of the thesis is shown below.The first chapter introduces the background and the significance of the subject.An overview of the TCM is given and the history of the research in the systematic analysis of antenna is discussed in detail,as well as the common methods of decoupling for MIMO antennas.The second chapter introduces the physical meaning of the classical characteristic mode and the fundamental parameters involved when researching arbitary obstacles based on TCM,such as characteristic value and characteristic currents.The theoretical basis for guiding the antenna design is revealed and the basis performance parameters of MIMO antenna is proposed in this chapter.These're the basis of the following work.In the third chapter,characteristic modes tracking algorithms are proposed,which track characteristic modes across a wide frequency range.A UWB antenna element and a series of two-element UWB MIMO antennas are analyzed by TCM.It can be found that,by introducing the isolation structure,two main characteristic modes of the UWB MIMO antenna resonate in the same wideband.In addition,the characteristic currents are out of phase at different ports,which makes a high isolation over the ultra-wide frequency band.In the fourth chapter,two compact UWB MIMO antennas are proposed using the characteristic modes.Some parameters such as the S parameters,radiation patterns,radiation efficiency and envelop correalation coefficient are investigated by simulation.Parts of the performance are verified by measurement.Results indicate that the both antennas have good performance,which can be applied in practical UWB MIMO communication system.The last chapter shows the summary of the thesis and the outlook for the future work.