Low Sidelobe Multibeam Antenna In Ka-Band

With the progress of science and technology,the field of communication is developing rapidly.In order to solve the problem of scarcity of spectrum resources,millimeter-wave band has become a research hotspot.However,because of the high frequency,millimeter wave has some disadvantages,such as high loss and low transmission efficiency.Millimeter-wave multi-beam antenna can generate high-gain beams and realize scanning in space.Substrate integrated waveguide(SIW)combines the advantages of microstrip line and traditional waveguide,which has the advantages of low loss,small size,easy integration,and is very suitable for high-frequency transmission.Therefore,millimeter-wave multi-beam antenna based on SIW can effectively solve the shortcomings of millimeter-wave,and has important research significance.This paper mainly focuses on the research of SIW millimeter-wave multi-beam antenna.The main contents can be divided into the following points:Firstly,the principle and design method of SIW are introduced,and the related theory of slot antenna is discussed.The basic principle of one-dimensional scanning and two-dimensional scanning are understood through the linear array and plane array of slot antenna,which lays a theoretical foundation for the follow-up design work.Then,a SIW multi-beam pillbox antenna with reduced sidelobe is proposed.The antenna system can be divided into three parts: feeding port,quasi-optical system and array antenna.Reflector antenna has some problems,such as aperture blocking and high sidelobe level of edge beams.To avoid the problem of aperture blocking,the antenna system adopts a dual-layer structure.In order to reduce the sidelobe level of edge beams,two extra parabolic reflectors are introduced into the parabolic quasi-optical system placed on both sides of the central parabolic reflector.In addition,the sidelobe level can be further reduced by adding some metal posts to the antenna array.The proposed antenna,operating at 28 GHz,has been verified by measurements,showing good performance over an scanning range of ±45°,and the SLLs of all the beams are lower than-12 dB.Finally,a 4×4 two-dimensional scanning multi-beam antenna based on pillbox antenna and Butler matrix is proposed.Butler matrix can achieve fixed amplitude and phase distribution,and it has a flexible structure.However,the design of the Butler matrix is complicated.Pillbox antenna has simple structure and small size,but its form is fixed,so it is difficult to achieve two-dimensional scanning by itself.Therefore,this paper proposes a idea to combine Butler matrix with pillbox antenna to realize two-dimensional scanning.In this scheme,four pillbox antennas and four 4×4 Butler matrices are needed.The design process of a single pillbox antenna is the same as that of the previous one,which avoids aperture blocking and reduce the sidelobe.The 4×4 Butler adopts a double-layer structure.First,the devices are designed and simulated separately,and then all devices are cascaded.After cascading the Butler matrix with the pillbox antenna,a complete antenna system is obtained.As a demonstration,a prototype of the structure is designed,fabricated,and measured.The results show that the antenna can achieve two-dimensional scanning of 16 beams in half space.