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In this paper, a novel decoupling method without adding any decoupling structure is investigated, and it is able to apply to multiple-input and multiple-output (MIMO) antenna designs with dual and multiple elements. The decoupling mechanism applied in here is to change the electrical length of the radiators to manipulate the radiation pattern for obtaining pattern diversity and good isolation simultaneously. The design mechanism and procedures for realizing pattern diversity are presented. To validate the proposed method, a two-element monopole antenna array with inverted-L elements is initially studied with the isolation better than 20 dB. Next, a four-element MIMO antenna utilizing two different types of monopole elements is proposed to further verify the feasibility of the proposed decoupling method. Finally, an eight-element MIMO antenna operating at 3.5 GHz is implemented with a compact total size of $40\times 100$ mm2, and the measured isolations between two elements are better than 15 dB. Envelope correlation coefficient and channel capacity are calculated to evaluate the MIMO performance, and good results are obtained. The target application of the proposed design is for laptop, small cell base station, or WiFi box with multiple elements. [ABSTRACT FROM AUTHOR]

This paper presents a multiple-input and multiple-output antenna using a wideband decoupling structure for enhancing isolation. The decoupling structure is formed by a split ring, which consists of an inductive line and a capacitive gap to realize magnetic and electric coupling, respectively. By introducing the electric coupling in addition to the magnetic coupling, more degrees of freedom are obtained and the original coupling between antennas can be canceled out within a wide frequency band. Meanwhile, the performance of each antenna element is maintained, such as impedance bandwidth and radiation characteristics. Theoretical analysis and experimental verification are carried out. When the decoupling structure is placed between these two monopole antennas with edge-to-edge space of only 5 mm ( 0.04\lambda 0 at 2.5 GHz), more than 20 dB isolation is realized over the bandwidth of 2.3–2.9 GHz (24%) with S11 and S22 less than −10 dB. Moreover, the isolation levels reach more than 30 dB over the frequency band of 2.3–2.8 GHz. Compared with the previous related works using decoupling networks and neutralization line techniques, the proposed decoupling structure can provide higher isolation of over 30 dB in a wider bandwidth. [ABSTRACT FROM PUBLISHER]