Research On MIMO Antennas Based On Single Radiator

It is full of challenges and difficulties to put multiple antennas together closely while maintaining a high isolation.Many decoupling techniques have been reported previously,such as defected ground structure,the electromagnetic band gap(EBG),the coupled resonator decoupling networks(CRDN),diversity technology,and so on.In these works,decoupling structures are adjunctions of the multiple antennas matched in advance;moreover,the decoupling design of the antenna has a strong dependence on the simulation software.In this research,the matter of isolation is discussed prior to the return loss in the design of MIMO antenna.Primarily,the isolation characteristics of the two port circuit network are established and analyzed.Then this non-radiation circuit is used to derive a structure with enough radiation,meanwhile the character of port isolation is preserved.Based on this design method of single radiator MIMO antenna,a dual frequency circuit model consisting of LC circuits is also presented,and it is introduced into the decoupling of dual frequency monopole antennas,and its feasibility is verified.The main research contents and works of this thesis are as follows:Firstly,a linear dual frequency single radiator MIMO antenna is designed.Firstly,based on the proposed linear dual frequency two-port passive circuit model,the conditions of port isolation are derived.Then the isolation condition obtained of the circuit model is verified by ADS software.Finally,the passive circuit model is evolved into a MIMO antenna with radiation characteristic.Through the optimization,a dual-band single radiator MIMO antenna is designed,and the antenna is fabricated and measured,which verify the effectiveness of the method.Secondly,two dual-port single radiator MIMO antennas are designed,respectively.The structure of the first antenna is ring-shaped.At first the circuit model composed of two parallel transmission lines with unequal impedance is analyzed,and the condition of the port isolation is deduced.The parameters affecting the isolation performance of the antenna are also analyzed.Secondly,on the basis of the designed circuit model,the corresponding antenna structure is built.Finally,through matching circuit and parameter optimization,the antenna has good radiation ability under the condition of isolation.The second antenna is a structure of a ring with end-stubs.Based on the ring circuit model,a ring dual frequency circuit model with open stubs is established.After analyzing the transmission characteristics of the circuit model,the condition of port isolation is obtained.Then the circuit model is converted into the micro-strip lines with isolation characteristics.By designing a matching circuit,the antenna has a good S parameter performance.The two antennas are tested through physical tests.Finally,a dual-band MIMO antenna is designed.The radiator structure consisted by two dual-band monopole antennas and a decoupling structure.We propose a circuit model with isolation characteristics composed of three series LC circuits,and the related parameters affecting the isolation characteristics are analyzed,and the influence of the related parameters on the isolation characteristics are also analyzed.Then the radiator consists of two dual-band monopole antennas and the micro-strip line mode corresponding to the circuit model.After optimizing the antenna size,the final MIMO antenna has high ports isolation in the two working frequency bands,and the results have been verified.