Electromagnetic Metasurface Research For Broadband RCS Reduction

In modern warfare,the stealth characteristics of military equipment are important indicators for measuring the performance of weapons and equipment.In the complex electromagnetic environment,superior stealth performance can effectively improve the survival rate of the equipment,thus fully guaranteeing their own combat effectiveness.As the"eye"of conventional combat weapons such as airplanes,missiles and ships,radar antennas are important devices for transmitting and receiving information.Their radiation characteristics need to meet operational requirements.At the same time,under the reconnaissance of enemy radars,it is also the radar cross section of the entire weapon.(Radar Cross Section,RCS)is the main source of contribution,so it also has high requirements for its scattering characteristics.It is in this application demand that this paper studies how to reduce the in-band and out-of-band RCS without affecting the normal radiation performance or even improving the radiation performance of the antenna when the antenna is in operation.The main work of this thesis can be summarized as the following aspects:Firstly,the application of artificial magnetic conductor(AMC)in the RCS of the microstrip antenna is studied.The AMC consists of three different types of artificial magnetic conductor units,which are arranged in a hexagonal structure by arranging the two units in two or two corresponding periods,and then cyclically extending outward along each side of the hexagonal structure.An array of different cells has an ideal reflection phase difference in different frequency bands,so that the respective reflected waves have equal amplitudes and a phase difference of 180~°.According to the principle of phase cancellation,the energy in the main direction is scattered to other directions.In order to verify the influence of the AMC on the antenna radiation,the AMC is loaded on the upper surface of the microstrip antenna dielectric substrate and compared with the reference antenna without the AMC loaded.Finally,on the surface of the simulation and measured results,loading AMC has little effect on antenna impedance matching and radiation characteristics.Comparing the scattering characteristics of the two,the designed antenna has a good RCS reduction effect in the broadband under the vertical illumination of the x-polarized and y-polarized incident waves,covering the in-band and out-of-band of the microstrip antenna operating band.Secondly,the application of Polarization Conversion Metasurface in low profile high gain dipole antennas is studied.The polarization conversion unit is periodically arranged to form a 6×6 array structure as a reflector of the dipole antenna.Due to the characteristics of the phase rotation of the polarization conversion surface of the polarization conversion surface,the thickness requirement of?/4 when the PEC is used as the reflection plate is avoided,so that the antenna profile is reduced.At the same time,the induced current near the surface of the super-surface structure of the dipole antenna unit increases the antenna aperture,so that the antenna gain is improved.Thirdly,the application of PCM in the realization of radiation wave polarization conversion is studied.The PCM is used as a dipole antenna reflector,and the antenna radiation wave and the reflected wave have the same amplitude and the phase difference is 90~°,and the two are superposed to form a circularly polarized wave.That is to say,the loading of the polarization conversion surface realizes the conversion of the dipole antenna element radiation wave from linear polarization to circular polarization.Fourthly,the application of PCM in the reduction of RCS in the wide band of array antennas is studied.The polarization conversion unit array and its mirror element array are arranged in the same plane as a reflector of the dipole array antenna and compared with a reference antenna to which the metasurface is not loaded.The final simulation and test results show that the matching characteristics and radiation pattern of the reference antenna and the designed antenna are more consistent.Comparing the scattering characteristics of the two can be obtained,and the designed antenna has a good RCS reduction effect in a wide frequency band including the working frequency band.