| Reconfigurable antenna can meet the needs of multiple scenarios and applications by loading electronic switches or employing mechanical methods to adjust its electrical characteristic parameters according to environmental changes.Parallel transmission channels are set up in space by the MIMO system,and the spectrum efficiency is greatly improved.Meanwhile,the bit error rate of the signal is reduced,resulting in improved signal quality.The flexibility and channel capacity of the MIMO system can be increased by applying reconfigurable antennas to the MIMO system.This paper focus on the reconfigurable MIMO antennas and the main work is summarized as follows:1.Firstly,a frequency reconfigurable antenna is designed.The stepped radiating element is used to improve the impedance matching over the UWB band.In order to achieve the single-band operation,a shorted slot ring resonator is embedded on the ground plane to suppress the high-frequency component of the UWB band.A rectangular open-ended slot is etched on the radiating element to introduce a notch-band,and that dual-frequency operation is obtained.Ideal switches are placed in the shorted slot ring and the open-ended slot,and the UWB,single-band and dual-band modes can be reconfigured by controlling the states of the switches.Then,a frequency reconfigurable antenna with complementary performance is proposed,which can operate in dual-band mode and dual-band notched UWB mode.The UWB operation is realized by the stepped radiating element and the truncated ground plane.A shorted slot ring resonator is loaded on the ground to achieve high-frequency suppression.An open-ended slot and an L-shaped slot with a rectangular stub are etched in the radiating element to generate two notch-bands.The frequency complementary performance is obtained by loading switches on the shorted slot ring and the rectangular stub.Finally,a MIMO array consists of two antenna elements placed opposite with eachother.The simulated and measured results indicate that the proposed MIMO antennas have good port characteristics and diversity characteristics.2.A polarization reconfigurable MIMO antenna is designed.An aperture-coupled patch antenna is used as the radiating element.A cross-shaped slot loaded with PIN diodes is etched on the ground,and the±45° linear polarization can be realized by controlling the states of the diodes.Four slots loaded with PIN diodes are etched at four corners of the patch,and the left-handed and right-handed circular polarization modes can be realized by changing the ON/OFF states of the diodes.The simulated and measured results show that the antenna can operate in ±45° linear polarization,left-hand and right-hand circular polarization modes.The overlapped bandwidth of four modes is 2.7%,and the isolation is greater than 15 dB.3.A pattern reconfigurable MIMO antenna is designed.The antenna element is composed of a rectangular monopole and two sets of parasitic element loaded with PIN diodes.The parasitic bending strips can operate as a reflector or a director by turning the diodes on or off,and then the antenna element can work in two directional modes and one bidirectional mode.A MIMO array consists of two antenna elements placed opposite with each other.A set of decoupling meandering strips is employed between the antenna elements to improve the isolation.Considering the operating modes of antenna element,the MIMO antenna can operate in nine modes.The simulated and measured results show that the overlapped bandwidth of the nine modes is 10%,and the isolation is greater than 16.5dB. |
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