Research On Decoupling Network Technique For MIMO Antennas

(Multiple Input Multiple Output) MIMO technology requires low correlation between antennas, the decoupling network has a unique advantage to design the antennas and the decoupling network separately, which can help simplifying the designing process of MIMO antennas. This paper is centered on how to build a lossless decoupling network for symmetric two antennas at any frequency, the lossless decoupling network is proposed by even-odd mode analysis method, it can achieve decoupling and matching effect simultaneously, moreover, the proposed decoupling and matching network can be applied to the miniature and band-broadening process of MIMO antennas. Main contents of this thesis are as follows:Firstly, the Π-shaped equivalent port circuit for symmetric two antennas is proposed using even-odd mode analysis method, the condition of decoupling and matching is concluded, which is to match the even/odd mode equivalent impedance to the characteristic impedance simultaneously. Afterwards, the conditions can be found to design the proposed decoupling network.Secondly, even-odd mode analysis proves that the 4-port all-connected lossless decoupling network has two redundant freedoms, the number of reactive components can be reduced for easier realization, which results in 14 possible simplified topologies. The constraint conditions on input even–odd mode equivalent impedances of every simplified DMN are discussed in detail. The proposed decoupling network is validated through simulation and experiment.Finally, the proposed decoupling network is applied to the miniature and band-broaden process for symmetric two antennas, the antennas which operate at a high frequency can be “pull down” to a low frequency by the proposed decoupling network, thus the miniature design can be achieved, the method of combining two lossless DMNs which operate at adjacent frequencies can help broadening the bandwidth to about two times as much as possible. The proposed decoupling network is validated through simulation and experiment.