Design Of Passive Multi-beam Antenna Based On Butler Matrix

With the development of mobile communication technology,the demand for communication capacity is increasing.A multi-beam antenna can generate multiple high-gain beams covering a certain area at the same radiation aperture.Multi-beam antennas can achieve frequency reuse,thereby increasing the available bandwidth,greatly increasing the communication capacity,and making fuller use of spectrum resources.In addition,multibeam antennas can conveniently implement shaped beams,Because of these advantages,multi-beam antennas are widely used in mobile communication and satellite communication systems.This paper mainly studied passive multi-beam antennas based on Butler matrix.Butler matrix is a passive beamforming network.It can produce signals of equal amplitude and equal phase difference at the output ports.Compared with other matrix beamforming networks,the Butler matrix has the advantage of requiring the least number of components to implement the same number of beams.It has the advantages of simple structure and lower cost when implementing fewer beams.At the same time,the port isolation is very high,so it has been widely researched and applied.The previous chapters of this article introduced the Butler matrix principle,array antenna theory,and substrate integrated waveguide technology(SIW).For the different applications of UHF frequency band and millimeter wave frequency band,two passive low-sidelobe multi-beam antennas based on Butler matrix are designed.One is the 690MHz-820 MHz dual-polarized low-sidelobe multibeam antenna based on the microstrip structure;the second is a miniaturized 28 GHz millimeter-wave low-sidelobe multibeam antenna based on SIW technology.1)A 690MHz-820 MHz dual-polarized low-sidelobe multibeam antenna was designed based on the 4×4 Butler matrix.The main components of the feed network include 3dB directional couplers,45-degree phase shifters,and ? attenuations.In this paper,the feed network has been miniaturized and broadband designed.Directional couplers use microstrip three-branch line couplers,the size of the three-branch line coupler is reduced by half by loading open branches.A broadband 45-degree phase shifter was designed using a short-circuited quarterwavelength resonator.Its relative bandwidth has reached 33%,and miniaturization has been achieved by bending microstrip lines.Avoiding the use of cross junctions on the Butler matrix layout further reduces the overall size of the feeding network.The antenna array element uses crossed dipoles,which can achieve +45° and-45° polarizations.The multibeam antenna has four ports,corresponding to two polarizations and two beam directions(±13°).The horizontal half-power beam width is 29°,and the vertical half-power beam width is 44°.The maximum gain of the beam is 9.3 dBi,the side lobe level is lower than-22 dB,and the cross polarization level is lower than-25 dB.2)A 28 GHz low-sidelobe multibeam antenna was designed based on the substrate integrated waveguide technology.Aiming at the application requirements of low side lobes,this paper proposes a new double-layer 4×8 Butler matrix topology.The unequal output is achieved by cascading unequal power dividers at the output ports of the 4×4 Butler matrix.The double-layer dielectric substrate structure can greatly reduce the use of cross couplers and reduce the overall size of the feeding network.The main components of the beamforming network include SIW-based directional couplers,phase shifters,unequal power splitters,and cross junctions.The antenna radiating part adopts an 8×8 longitudinal slot array,and the antenna array and the feeding network are directly integrated together.The overall size of the multi-beam antenna is 162mm×56mm,and it can generate beams in four directions of ±15° and ±47°,respectively.The gain of the ±15° beam is 20.3 dBi,and the half-power beam width is 16.5°.The gain of the ±47° beam is 18.6 dBi,and the half-power beam width is 22°.The sidelobe level of the beam is less than-18 dB.