Design Of Millimeter Wave Array Antenna In Synthetic Aperture Radar

Synthetic Aperture radar（SAR）is an imaging radar,which is widely used due to its superior high resolution characteristics.It transmits and receives signals from the antenna and stores the received signals.The stored signals are superimposed and processed by digital signal processing technology to form images.It can be seen that antenna is the key hardware subsystem of SAR system,so it is necessary to improve the performance of SAR system through the research and design of antenna system.Airbornne SAR has a broad market in both military and civilian areas.With the progress of science and technology,the requirements of SAR system for antennas are more focused on miniaturization,high gain,broadband,low sidelobe and other aspects.With the development of communication technology,the use of low-frequency microwave signals is becoming more and more saturated,so many scholars have begun to study the microwave communication technology of higher frequency.For example,millimeter wave frequency band and terahertz frequency band have been the focus of research in recent years.However,the antenna of high frequency band is small in size and sensitive in device,so it is difficult to design,manufacture and debug.By considering the advantages and disadvantages of various common antenna forms,the design of millimeter wave antenna in SAR system is carried out by using Substrate Integrated Waveguide（SIW）.This article adopts the SIW structure to design a rectangular structure slot array antenna,which combines the Taylor distribution function to control the feeding amplitude of the array and the bias distance of the slot,so as to effectively control the sidelobe level of the array on the azimuth plane and the pitch plane.At the same time,SIW structure is used to design the feed network to realize the unequal amplitude feed of the array and reduce the loss.The experimental results show that the S₁₁amplitude of the antenna is less than-10d B in the33.3GHz-36.54GHz band,and the relative bandwidth is 9.3%.The maximum gain of the antenna is 18.56d B,the level of side lobe of plane H is less than-20d B,and the level of side lobe of plane E is less than-18d B.Subsequently,a SIW diamond slot array antenna was designed,and the antenna bandwidth is expanded by changing the form of the radiation gap.Firstly,the design experiment is carried out by the line array,and the impedance bandwidth is widened from the original 7.13%to10.4%,so as to verify the correctness of the expanded bandwidth of this slit structure.Then,the front array is designed and compared with the rectangular slit.It is extended from 9.3%to13.68%,and the index requirement of low sidelobe is also realized by combining with Taylor synthesis method.However,with the development of communication technology,the application range of linearly polarized antennas is limited,and it is difficult to meet higher usage requirements.In practical applications,circularly polarized antennas have received more widespread attention.Therefore,in this paper,a miniaturized,low-profile circularly polarized antenna is designed with the SIW back cavity structure.The resonant cavity of the back cavity antenna is designed with the SIW structure to suppress the downward radiated electromagnetic wave and reduce profile.Introduce a pair of rotating triangular patches in the radiation layer to from a circularly polarized wave to radiate energy.According to the experimental results,the antenna operates at 26-31GHz with a relative bandwidth of 18%and an axial bandwidth of 11.1%.