| Focusing antenna is a kind of antenna which can concentrate most of the electromagnetic wave energy in a small range to form a certain focal spot.It is widely used in microwave and plasma measurement,wireless energy transmission,millimeter wave imaging and other fields.However,most of the existing focusing antennas face problems such as spatial resolution to be optimized,only working in a single frequency band,poor structure and oblique incidence stability,which will further limit the development of the focusing antenna.In view of the above problem,on the premise of ensuring the focusing performance,this article aims at improving the spatial resolution,miniaturization design,dual-band focusing and improving the antenna stability in harsh environment,which is of great significance.The main research contents and innovation points of this article are as follows:1.A focusing transmitarray antenna based on I-shaped unit is proposed,aiming at the characteristic that the spatial resolution of existing focusing antennas still needs to be further improved.In order to make as many units distributed on the transmitarray as possible and make it more precise in the regulation of electromagnetic waves,by bending the slot line in the unit several times to form an I-shaped method,the period size of the unit is greatly reduced,and the period size of the unit is greatly reduced.The miniaturization of the unit;in addition,by optimizing more degrees of freedom in the unit,the required transmission parameters are realized,and at the same time,less than 45% of the entire unit is covered with metal and no dielectric layer.The weight of the transmitarray is reduced,and the weight of the unit is realized.360° full phase coverage can be achieved by optimizing the size parameters of the I-shaped unit.By theoretically deriving the phase distribution on the transmitarray,the design of the focused transmitarray antenna is completed.Due to the miniaturization of the unit,more I-shaped units can be placed under the same array aperture area.It is beneficial to improve the focusing performance of the entire antenna.Simulation and experimental results show that the proposed focusing transmitarray antenna achieves the required focusing performance at the center frequency.2.A dual-band focusing transmitarray antenna is proposed,in view of the fact that most of the existing focusing antennas can only work in a single frequency band,and multi-band is a very important index parameter in antenna design.Based on this,using the combined unit method,two different types of transmission units are integrated.By analyzing the induced electric field and transmission parameters of the integrated dual-band unit,and comparing them with the transmission parameters of different types of units before integration,the effectiveness of the combined unit method is verified.The phases of the units at each position of the transmitarray are independently analyzed under different frequencies,and the design of the dual-band focusing transmitarray antenna is completed.The results show that the-3d B focal spot size of the proposed antenna meets the requirements at 12 GHz and 18 GHz,and the focusing performance of the proposed antenna in different frequency bands is verified.3.Focusing transmitarray antennas based on metal waveguide structure is proposed,in view of the the fact that most of the existing focusing transmitarray antennas have a dielectric structure which is easily affected by the external environment,the unit structure has been completely improved.Instead of the traditional dielectric structure,by embedding a metal waveguide structure between every two phase shift layers of the transmission unit to reinforce the transmitarray,and the multi-physics analysis platform is used for modeling and simulation,and the structural deformation of transmission unit in high temperature environment is analyzed.In addition,in order to achieve excellent transmission performance while reducing processing complexity,the transmission unit achieves 360° full phase coverage at the center frequency by changing the length of the II-shaped slot.The results show that the designed frequency selective surface can converge the electromagnetic waves from the feed antenna obviously,and the-3 d B focal spot size is better than twice the wavelength.In addition,on the basis of the previous II-shaped slot unit,the structural parameters of the improved unit are further optimized,and a double scoop-shaped slot unit is gradually obtained.In comparison,the optimized unit has a smaller period size,and the simulation results show that the double scoop-shaped slot unit has excellent oblique incidence stability,which helps to improve the transmission performance of the edge region of the transmitarray.In addition,the focusing transmitarray antenna working at two different frequencies of high and low are obtained through the method of proportional change of unit parameters,and the focusing ability of the two antennas is verified through simulation analysis,which simplifies the design process of focusing transmitarray antennas at different frequencies,verify the focusing performance of the antenna.In summary,this article has carried out in-depth research on focusing transmitarray antennas.The proposed antenna has excellent spatial resolution,while achieving good results in miniaturization,dual-band operation,and the antenna stability.It is of great value and significance for the development of high performance focusing antennas. |
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