Research On Reconfigurable Antenna Based On Liquid Materials

With the rapid development of modern wireless communication system,the communication system needs to have the characteristics of large capacity,multi-function and ultra-wideband,which often requires multiple antennas to meet.First of all,in order to reduce the size of the system,it is necessary to reduce the size of the antenna.Therefore,the reconfigurable antenna with the advantages of multi-operation,high efficiency and miniaturization has attracted extensive attention.Secondly,with the development trend of antenna integration,the problem of electromagnetic coupling between antennas becomes more and more serious.In this thesis,reconfigurable antennas,liquid materials and decoupling technology are combined to design frequency reconfigurable antennas based on liquid metal and continuous frequency and isolated MIMO antenna array based on liquid medium respectively.Finally,it is proved that the decoupling technology not only improves the isolation between antennas,but also improves the channel capacity of MIMO antenna array.Firstly,this thesis studies the basic principles and implementation methods of cylindrical dielectric resonator antenna(CDRA),antenna decoupling technology,frequency reconfiguration and channel capacity evaluation,and has a deep understanding of the following research work in theory.1.A frequency reconfigurable dielectric resonator antenna is proposed by controlling the electrical length of liquid metal.A circular polycarbonate(PC)container with four microchannels is nested outside the cylindrical dielectric resonator antenna fed by the probe to provide reconfiguration conditions.Among them,the liquid metal in the microchannel is connected with the metal ground,and the change of the height of the liquid metal affects the field distribution of the dielectric resonator antenna,thus realizing frequency reconfiguration.Compared with dielectric resonator antennas of equal size,the air gap between dielectric resonator antennas proposed in this thesis greatly increases the quality factor and reduces the resonance bandwidth,so the resonance of antennas can’t cover each other to produce full bandwidth.Therefore,the broadband characteristics become multi-frequency characteristics.On the other hand,by reducing the effective dielectric constant and increasing the bandwidths of all newly generated frequency bands,the mixed resonance modes with narrow bandwidths can be excited to obtain multiband characteristics.2.A continuous frequency and isolation reconfigurable MIMO antenna array with NL decoupling structure by controlling the equivalent dielectric constant of liquid medium is designed.The antenna consists of two oppositely placed PIFA(Planar Inverted-F Antenna)antennas,and a pair of transparent boxes made of PC(dielectric constant is about 2.7)are loaded between the radiation patch and the floor to provide reconstruction conditions.By adjusting the height of pure water from 0mm to 9.15 mm,the frequency reconfigurable range is 1.58 GHz to 1.08GHz(the frequency tuning range is 37.5%).Pure water in the water tank made of PC will not only disturb the electric field distribution near the antenna,but also change the equivalent dielectric constant of the whole water tank.In the reconfigurable range of 1.08GHz-1.58 GHz continuous frequency,the isolation in the working frequency band is improved by at least 8d B due to the loading of the neutral line.Subsequently,the antenna was processed and measured.From the results,it is obvious that the measured results of vector network analyzer and spherical near-field are basically consistent with the simulation results of commercial HFSS software,and the isolation degree is improved in some states compared with the simulation results,which verifies the feasibility of the scheme.3.The influence of decoupling structure on the channel capacity of MIMO antenna array is mainly studied.Firstly,the comparison results of channel capacity before and after decoupling of reconfigurable antenna based on continuous frequency and isolation of liquid medium are given and analyzed.Secondly,according to the principle of spatial cancellation and the principle of electromagnetic lens,the dielectric cladding structure is designed.By controlling the amplitude and phase of the reflected wave to meet the condition of equal amplitude and opposite phase with the directly coupled electromagnetic wave,the electromagnetic interference of adjacent or close antennas and the reception of useless signals are reduced,and three dielectric cladding structures with different materials are designed.On the one hand,the influence of three kind of dielectric cladding structures made of different materials applied directly above the 1×2 base station antenna array on the isolation is analyzed.On the other hand,through the joint simulation of HFSS-MATLAB,the comparison of channel capacity before and after adding dielectric cladding and the comparison results of the influence of three different dielectric cladding structures on channel capacity are given.The effectiveness of the cladding structure in improving the channel capacity of antenna array is verified.