| The planar reflectarray antenna is composed of a reflection front and a space feed.Because of its advantages of small profile,high gain,low cost,and easy processing,it is more and more widely used in commercial,civil and military applications.Among them,the planar reflectarray antenna with beam scanning capability based on mechanical tuning,electronic component tuning,and liquid crystal tuning is even more sought after.Liquid crystal tuning,as a follow-up technology of mechanical tuning and electronic component tuning,solves the problems of high complexity and difficulty in applying to high frequency bands in these two tuning technologies,so it has received more and more attention.The main contents of this thesis are as follows:A reflectarray unit cell working in x-band was designed.The radiation patch of the reflectarray unit cell is composed of open ring,ring and circular patch.The overall structure of the radiation patch is center symmetrical and avoids the introduction of complex and irregular structure,which provides convenience for the subsequent array processing.By changing the radiation patch size of reflectarray unit cell,the phase shift range of the reflectarray unit cell is not less than 550 °,and its phase shift sensitivity is low,which is suitable for the design of the planar reflectarray antenna working on x-band.At the frequency of 10 GHz,simulation and tests were carried out on the array with the main beam direction of(0 °,0 °)composed of the reflectarray unit cell.The test results are similar to the simulation.The main beam direction of the planar reflectarray antenna is located in the direction of(0 °,0 °)without obvious angle deviation,and the main beam gain reaches about26.5 d Bi,sidelobe suppression is about-12 d B,and the beam width of 3 d B is about 6 °.The directional performance of the planar reflectarray antenna is good.The planar reflectarray unit cell based on liquid crystal tuning was studied,and two unit cells were designed.First,by setting the dielectric constant of the liquid crystal to change from 2.4 to 3.2,the simulation realizes that the two unit cells have a phase shift range of not less than 310 ° at the center frequency of 28 GHz,and the bandwidth of the two unit cells to achieve a phase shift of about 300 ° in the frequency range of 24 GHz-34 GHz is about 10.7%.Secondly,two types of reflectarray unit cells were machined and tested.The test used two types of liquid crystals,5CB and E7,and spacers with two thicknesses of 0.168 mm and 0.203 mm.The test shows that the best test results of the two unit cells are: a phase shift of about 105 ° at 25.2 GHz with a maximum loss of about 24 d B;a phase shift of about 75 ° at 26.05 GHz with a maximum loss of about 18 d B.Then,the phase difference of the measured phase shift curve was fitted with the simulation,and it was obtained that the variation range of the dielectric constant of the liquid crystal(5CB)in the experiment was about 2.7-2.84 at about 25.5 GHz.Finally,the unit cells with the center of the radiating patch as the cross-shaped patch were arranged in an array,and the scanning simulation of the main beam from(-45 °,0 °)to(+45 °,0 °)was carried out in HFSS. |
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