Researches On Wide-Angle And Low-Sidelobe Scanning Of Planar Microstrip Phased Arrays

With the specialty of fast scanning,the phased array is irreplaceable in the applications in radar,communication,and so on.In order to enhance the scanning range of phased array,researchers pay more attention to the wide-angle scanning phased array and the optimization of the scanning lobes.In this dissertation,planar microstrip phased array has been studied for the wide-angle scanning and the optimization of the scanning lobes and the main contents are introduced as follows.The first part mainly focuses on the discussion of the design and theory of the element antennas with wide beamwidth.At first,equivalent magnetic current is generated by the slots on the planar microstrip antenna.The different radiation characteristics of the magnetic current and the electric current with an infinite metal ground are analyzed.According to the boundary conditions and the image theory,magnetic current is beneficial for the acquisition of wide beamwidth or low elevation radiation lobe for the planar microstrip antenna.The proposed antenna is designed by this theory with wide beamwidth or low elevation radiation lobe.Secondly,substrate integrated waveguide(SIW)slot antenna is designed.According to the analysis of theory and simulation,relationship between the configuration of the slots and the radiation of the antenna can be got.A suitable configuration of the slots can help the antenna obtain wide beamwidth of radiation.At last,magnetic current and electric current have been combined on the microstrip antenna which is an ME dipole,and a circularly-polarized radiation pattern is generated.The generation of the magnetic current and the electric current is analyzed.Besides,amplitude and phase between the magnetic current and electric current can be adjusted by the size of antenna.The vertical polarized radiation and the horizontal polarized radiation are combined with the same amplitude and a 90° phase difference,and a circularly-polarized radiation pattern is generated.With these theories,four kinds of microstrip antennas with wide beamwidth are proposed.It lays the foundation for the study of wide-angle scanning of phased array antenna.The second part mainly shows the study on the wide-angle scanning of planar microstrip phased array.The specifics of different phased arrays are discussed.At first,microstrip magnetic dipole phased array and microstrip magnetic Yagi subarray phased array are proposed and analyzed.In the phased array,coupling patches are discussed emphatically.The coupling energy is transmitted between the elements by the coupling patches.Besides,the beam of active radiation pattern is wider than the one in the free space.The scanning range is enhanced sharply.Secondly,the SIW slot antenna works as the elements for the phased array.Rows of metal vias are set between the elements and the equivalent electric walls ensure a stable mode field for the element.The bandwidth is 17% for the active elements.Besides,the phased array can obtain wide-angle scanning in the working band.Thirdly,the ME dipole is worked as element in the phased array.The influence to the polarization and beamwidth of active radiation pattern from array structure is analyzed.With a reasonable size,the phased array can scan its main lobe with circular polarization in a wide-angle range.At last,TM010 mode and zeroth-order resonance(ZOR)mode are generated on the planar square microstrip antenna at the same time.The radiation pattern of the two modes can filled up each other and wide beamwidth can be generated in the upside space.A 6×6 plane microstrip phased array is fabricated by this antenna.A wide-angle scanning with dual-polarized lobe is generated in the 2D space.The third part mainly focuses on the optimization of the sidelobe in the wide-angle scanning range with microstrip magnetic dipole phased array.Firstly,genetic algorithm is applied on the array factor.The active radiation pattern calculated by the CST is used as the elements in the factor,in order to take into account the impact of coupling.The results show that the sidelobes have been reduced in the wide-angle scanning range with this way.Further more,neural network prediction method is used to simulate the scanning beam of the phased array instead of the array factor.The neural network is trained with a feedback neural network.Coupling and mismatch are not appeared in the neural network prediction,so the result is more accurate.The result from the neural network is optimized by the genetic algorithm.The measured and simulated results show that sidelobes of the phased array are reduced in the wide-angle scanning range by this way.