Metamaterial Antenna And MIMO System Of Terminals Research For Next Generation Wireless Communication System

With the arrival of the fourth generation(4G) mobile communication era, mobile communication systems need larger capacity, higher data rates and better quality of service. On one hand, the frequency bands of 4G communication are broadened further. The development trend of the wireless terminal antennas is wide-band, multi-band and high performance, while smaller space is reserved for antennas. Therefore miniaturization of antenna design becomes particularly important. On the other hand, the use of multiple input multiple output(MIMO) communication system results in higher channel capacity and link reliability, which would be one of most promising wireless technologies for broadband communication applications. According to the wireless terminal technology of MIMO antennas, it is a great challenge to place multiple antennas in a small space and ensure the independently effective working of each antenna in a limited volume of wireless terminal devices. Based on the hotspot developed direction of the current wireless terminal equipment, this thesis adopts some new ideas by introducing the concept of metamaterials. The main research of this article is miniaturized antenna design based on zeroth-order resonance of composite right and left handed transmission lines(CRLH-TLs), high isolation MIMO antenna design and specific absorption rate(SAR) suppression of terminal antenna by loading resistive absorbing materials. The object is to achieve a multi-band mobile phone antenna with miniaturization and high performance.The thesis introduces the basic theory of metamaterials, including the principle of left-handed materials(LHM) and its unique electromagnetic properties. And the propagation characteristics of electromagnetic waves in LHM are also derived. The theory of the CRLH-TLs and its equivalent circuit model are discussed, and the implementation and application of CRLH-TLs are introduced as well. Meanwhile, the chapter also focuses on the basic principle of MIMO antenna technology, as well as on the definition and standard of SAR. For the terminal equipment, the basic environment of SAR testing is described.A novel smart mobile phone antenna covering LTE band is proposed based on the theory of zeroth-order resonance of composite right and left-handed(CRLH) transmission line, which can be used to design a multi-band miniaturized antenna. By means of producing the equivalent left-hand capacitor and left-hand inductor, the theory of zeroth-order resonance(ZOR) is particularly recommended to design antenna. In the meantime, the ground current is also used to achieve miniaturization. The proposed ZOR antenna covers LTE747/GSM850/900DCS1800 /PCS1900/UTMS/LTE2300/2600 with good performance of radiation pattern, high gain and high efficiency, which can meet the requirement of a LTE smart mobile phone. The operating characteristics of the proposed antenna on the performance are also analyzed. The measured results of the fabricated antenna are in good agreement with the simulated antenna. It confirms that the fabricated ZOR antenna has the advantages of miniaturization and good performance.Several MIMO antennas decoupling methods are introduced to improve the isolation between antenna elements. A four-cell antenna MIMO system is built, which consists of four zero-order resonance antennas. Mutual coupling between antenna elements which are placed in four different positions is discussed. The S parameters of the system and the envelope correlation coefficient of Envelope Correlation Coefficient(ECC) simulation are also analyzed. We select two ways of antenna placement to achieve higher isolation between antenna elements by different methods of loading meander line and defect ground structuresFinally, a dual ZOR mobile phone antenna model is chosen as the basic model. By comparing a set of results with resistive surface material in different ways, it is verified that resistive surface material can reduce antenna radiation power towards the head direction, and further reduce SAR values. Meanwhile the two models of periodic R-Cards and the R-Cards loading frequency selective surface(FSS) are analyzed. They are used to look for methods of SAR reduction and antenna radiation efficiency maintenance as well, in order to achieve better performance.