A miniaturized ultra-wideband multiple-input multiple-output (UWB MIMO) two-port antenna with high isolation based on FR4 is designed in this article. The size of the antenna is only 18 × 28 × 1.6 mm3. The MIMO antenna consists of two identical antenna elements symmetrically placed on the same dielectric substrate in opposite directions. By loading three crossed X-shaped stubs between two unconnected ground planes, high isolation and good impedance matching are achieved. The working frequency band measured by this UWB MIMO antenna is 1.9–14 GHz, and the isolation is kept above 20.2 dB in the whole analysis frequency band. Good radiation characteristics as well as envelope correlation coefficient (ECC, <0.09), mean effective gain (MEG), and channel capacity loss (CCL) in the passband meet the requirements of the application, which can be applied to the UWB wireless communication system. To verify the applicability of the proposed method for enhancing the isolation between antenna elements, the two-port antenna structure was extended to a four-port antenna structure. In the case of loading the X-shaped stubs to connect to the ground plane, the isolation of the antenna is maintained above 15.5 dB within 1.7–14 GHz.
For the ultra‐wideband (UWB) transmission requirements in wireless communication systems and better miniaturization of mobile terminal antennas, a compact UWB multiple‐input multiple‐output (MIMO) antenna with higher isolation between units is proposed. The MIMO antenna consists of two semi‐circular antenna units and a defective ground structure. By improving the structure of the ground plane, the antenna units are placed upside down by taking advantage of the inherent directional radiation characteristics of the antenna units, thereby achieving higher isolation. The proposed antenna size is 15 × 22 × 1.6 mm3. The measurement results show that the proposed UWB MIMO antenna satisfies the port reflection coefficient S11 < −10 dB in the 3.4–12.9 GHz band, and the isolation is all greater than 25 dB, which has high isolation. The allowable limit of the envelope correlation coefficient ensures good MIMO performance, which can meet the requirements of UWB wireless communication in practical engineering applications.
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