| With the development of wireless communication technology in the direction of software-defined radio—that is,the traditional hardware circuit is reconstructed by software to realize the multi-function of the system.As an important part of wireless communication system,antenna reconfiguration is bound to be one of the trends of antenna development in the future.The antenna can adjust the radiation beam dynamically to reduce the signal interference and improve the system security.The application of pattern reconfigurable antenna in MIMO system can increase channel capacity,improve SNR and further improve the performance of the communication system.Therefore,the pattern reconfigurable MIMO antenna has research value.At present,there are still some problems that need to be further studied,such as antenna miniaturization,antenna structure simplification,multi-frequency band,multi-state switching of pattern and improvement of MIMO antenna array isolation.MIMO technology can improve WLAN throughput,transmission speed,transmission distance and reliability.In this paper,three pattern reconfigurable antennas and one pattern reconfigurable MIMO antenna array for WLAN are proposed.The research contents are as follows:(1)Based on the requirements of dual-frequency and miniaturization,a structure of miniaturized pattern reconfigurable quasi-Yachi microstrip antenna is proposed.Based on the idea of switching radiation unit,radio frequency(RF)switch sets between the radiation unit and the feed point.By controlling the state of the RF switch,different radiation units are selected to reconstruct the pattern.The influence of the parameters on the antenna performance is analyzed through simulation,the simulation and measurement results are obtained after optimizing the parameters.The results show that the actual test results are in good agreement with the simulation results.Its common frequency band covers two WLAN bands of 2.4GHz/ 5.8GHz,the gain is greater than 4.7d Bi,and the antenna size is 55mm*55mm*0.8mm.Compared with the literatures,the antenna has the characteristics of dual-frequency miniaturization,simple reconstruction and high gain.(2)Based on the requirement of independent reconfiguration of two frequency band pattern,a high gain dual-frequency independent pattern reconfigurable antenna structure is proposed.A RF switch sets on the parasitical unit which becomes a guide or reflector by controlling the on-off of the RF switch to realize the adjustment of the beam.Two pairs of parasitic units working in high and low frequency bands are set up,the antenna can realize independent reconstruction of dual-frequency directional pattern,theoretically forming 16 different directional pattern combinations.The influence of the parameters on the antenna performance is analyzed through simulation,the results are obtained after optimizing the parameters show that the antenna covers all the WLAN 2.4GHz / 5.2GHz / 5.8GHz operating bands,the gain is greater than 4.5d Bi,and the antenna size is 55mm*55mm*1.6mm.Compared with the literatures,the antenna has the characteristics of simple structure,small size,double frequency band,high gain,and the pattern of each frequency band can be reconstructed independently.(3)In order to meet the requirements of the state of multi-pattern and cover a larger angle range,a structure of multi-pattern reconfigurable antenna is proposed.By switching four states of the switch in high frequency band which on the parasitizing unit,the antenna has nine kinds of radiation pattern,which can switch the directional/omnidirectional patter.In directional mode,eight 45° spaced antenna beams can cover the entire plane.The influence of the parameters on the antenna performance is analyzed through simulation,the results are obtained after optimizing the parameters show that the antenna covers all the WLAN 2.4GHz / 5.2GHz / 5.8GHz operating band,and the gain is higher than 5d Bi.Compared with the literatures,the antenna has the advantages of high gain and double frequency band in the finite size,and can produce nine kinds of radiation pattern.(4)A structure of MIMO antenna array with high isolation is proposed.Two high gain dual-frequency independent reconfigurable antennas are placed as non-spacing orthogonal arrays of element antennas to form a pattern reconfigurable MIMO antenna array,and high isolation between antenna elements is realized by using orthogonal polarization.Because the cell antenna has four modes,the MIMO antenna array can operate in sixteen modes.The simulation analysis of the three typical modes shows that the MIMO antenna common frequency band covers the WLAN 2.4GHz / 5.2GHz / 5.8GHz multi-frequency band,and the isolation within each operating frequency band is greater than-20 d B.The pattern can achieve omnidirectional coverage on the horizontal plane,and the gain is greater than 4.8d Bi.The analyzation of envelope correlation coefficient of MIMO antenna shows that the antenna has good diversity ability and is suitable for WLAN system. |
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