The Research Of Multi-beam Antenna Based On Butler Matrix

Multi-beam antenna can take advantage of the high gain and narrow beam of multi-beam antenna to achieve space coverage.Its low sidelobe can be used to suppress the interference and its beam synthesis can be achieved at RF side.With its low cost and easy implement,so we can use it to expand the capacity of existing communication system.Multi-beam antenna plays an increasingly important part in radar,mobile communication system and satellite communication system with its easy implement and accurate beam pointing.In this paper,we mainly study theory and technology of multi-beam antenna based on Butler matrix and design three kinds of antenna applied on radar based on X band.Firstly,a multi-beam antenna based on single-layer microstrip and 4×4 Butler matrix is proposed.A three-branch directional coupler is used as the 3d B directional coupler to broaden the bandwidth and a three U-coupled Schiffman phase shifter is used to produce 45 degree.A cross-junction is implemented with two cascaded directional couplers.For antenna unit,we choose the printed dipole antenna with integrated Balun.When four ports are fed respectively,the VSWR of the integrated antenna is lower than 1.5 and the maximum beam can cover ±36° space.The maximum gain of middle beam can obtain 9.3d Bi.The maximum gain of outside beam can obtain 8.5d Bi.For millimeter wave,the SIW can take lower loss than microstrip.Secondly,a multi-beam antenna based on double-layer SIW and 4×4 Butler matrix is proposed.A 3d B directional coupler I with broad-wall directional coupling and a 3d B directional coupler II with narrow edge coupling are proposed.An unequal-width phase shifter is used to produce-45 degree.This structure doesn't need a cross-junction,so it's lateral size can be reduced 50%.For antenna unit,we also choose the same printed dipole antenna with integrated Balun.When four ports are fed respectively,the VSWR of the integrated antenna is lower than 1.5 and the maximum beam can cover ±38° space.The maximum gain of middle beam can obtain 11.2d Bi.The maximum gain of outside beam can obtain 10.0d Bi.The SIW multi-beam antenna has more excellent performance than the microstrip multi-beam antenna.Then we fabricate and test the antenna with each measured VSWR of four ports is below 2.The measured pattern is consistent with simulation results.In order to achieve wider range of scanning,a multi-beam antenna based on double-layer SIW and 8×8 Butler matrix is proposed lastly.Additional design of a new form of phase shifter,cross-junction and phase compensation structure are required.For antenna unit,we choose the substrate integrated waveguide slot array antenna with five equal amplitude excitation to achieve high gain.Thus,its HPBW of E-plane can achieve 94°.When eight ports are fed respectively,the VSWR of the integrated antenna is lower than 1.5 and the maximum beam can cover ±62°space.The maximum gain of middle beam can obtain 16.9d B.The maximum gain of outside beam can obtain 13.7d Bi.