Investigation And Application Of Compact Planar Multi-band/ultra-wideband MIMO Antennas

With the rapid demand for high date rate and high quality mobile communication,the Long Term Evolution(LTE)is the mobile 4G communication standard expected to provide high data rate.As one of the core technologies of LTE mobile system,the multiple-Input-multiple-output(MIMO)technology has potentiality of increasing the spectrum efficiency and improving the data transmission rate.MIMO antenna as a key component of the LTE system has attracted significant research power in the recent years for its well-known advantages of increasing transmission capacity and reducing multipath fading.In the dissertation,the compact planar multi-band/ultra-wideband(UWB)MIMO antennas are studied and several kinds of compact planar multi-band/UWB MIMO antennas with good characteristics are presented.Furthmore,based on the real indoor experiment,these kinds of antenna feed system were studied and tested.The main contributions of the dissertation can be summarized as follows.(Ⅰ)Several kinds of compact planar multi-band monopole antennas and UWB antennas are studied and these antennas have good characteristics in compact size,planar and multi-band/UWB functions.The folded momopole antenna and coplanar waveguide(CPW)fed UWB antenna are successfully simulated,designed,and measured showing broadband matched impedance,constant gain and stable radiation patterns.Accordingly,the proposed antennas are expected to be good candidates for elements of MIMO antenna.(Ⅱ)Several kinds of isolation techniques of MIMO antenna are studied.Slitted ground is able to suppress surface wave(surface currents)propagation,and thus reduce strong mutual coupling.When ground branches are introduced,the coupling evoked by the excited antenna element and ground branch can be conteracted partly with the mutual coupling.Thus,the isolation of MIMO antenna can be improved.By introducing a neutralising line,the isolation can be improved greatly by neutralising the current of the two antennas when the phase of the currents is opposite,hence avoiding the need for extra space and design difficulty.The vertical polarization teniques is discussed to reduce the coupling evoked by the space wave(near field).All the decoupling methods aboved are verified by the simulation and measured results.(Ⅲ)Based on the study of MIMO antenna element and isolation,several kinds of compact planar multi-band MIMO antennas are presented.Besides,the diversity characteristics of MIMO antennas are also studied.Furthermore,based on the adventanges of UWB technique and MIMO technique,the UWB-MIMO antenna is proposed,which has good ultra-wideband and deverstiy characteristics.At the end of the chapter,dual band-notched UWB-MIMO antenna is proposed to minimize the potential interferences without increasing the sizes of antenna elements and the mutual coupling.(Ⅳ)Antenna design is for use.Based on the Ericsson real indoor experiment,three kinds of antenna feed system were studied and tested.It is found that the proposed antenna shows good characteristics in multiple bands at 900 MHz(890-960 MHz),1800 MHz(1710-1880 MHz),2300 MHz(2320-2370 MHz)and 2600 MHz(2575-2635 MHz).Moreover,LTE reference signal receiving power(RSRP),download speed and upload speed are pretty well.