Research And Design Of Multi-Beam Antenna

Multi-beam antennas can generate multiple beams with different directions through the same aperture.In many communication applications,the array antenna with microwave lens as the feed network is often used to achieve the characteristics of high gain beams and wide-angle coverage.Rotman lens is a multiple beamforming network(BFN)based on passive microwave lens,which has the advantages of low cost,high reliability,simple design,wide bandwidth,low phase error,and wide scanning angle.When different input ports on the focal arc are excited,microwave signals with different linear phase differences will generate on the array ports of the lens.When the microwave signals with different phase differences radiates into free space through the array elements,the wave front with different directions will be formed,that is,the multi-beam scanning characteristic will be achieved.Since the Rotman lens is a true-time-delay(TTD)device,the formed beam direction is independent of the frequency.In this thesis,the Rotman lens multi-beam antenna based on microstrip and substrate integrated waveguide(SIW)is mainly investigated,focusing on the improvement of traditional Rotman lens design method and the Rotman lens antenna to achieve wide-angle or very-wide-angle scanning characteristics.Firstly,the working principle and design equations of Rotman lens are analyzed through geometric optics(GO)method.A multi-beam network based on Rotman lens working on X-band is designed.When it is applied to a 32-element linear array,the multi-beam system can realize 13 independent beams within ±25° scanning range through theoretical analysis on simulated and measured results,respectively.Secondly,the basic characteristics and analysis of SIW are studied.Meanwhile,in order to achieve the connection between microstrip line and SIW,an isosceles trapezoidal transition is studied.To reduce amplitude and phase fluctuations within the entire working band,the side wall structure and port shape of the microstrip Rotman lens and several other places were deeply improved.A low-sidelobe SIW slot array is designed by using Taylor distribution at the center frequency of 10 GHz.Furthermore,a dual-layer SIW slot coupling phase shifter is adopted in this chapter to effectively reduce its overall dimension.Finally,the modified microstrip Rotman lens,the dual-layer phase shifter,and the 10×10 SIW slot array antenna are combined into a hybrid multi-beam antenna,which is compact in size and has a reduced lateral dimension.The antenna has 7 input ports,the E-plane radiation pattern of the antenna can achieve a maximum beam pointing of ±35° when different input port is excited.Finally,two multi-beam antennas with very-wide-angle scanning performance working at S-band and X-band are developed,respectively.Firstly,the design method of the Rotman lens is improved by modifying the design parameters under the requirements of very-wideangle scanning range because the focal arc and the inner contour differ greatly by using the traditional method.The improved Rotman lens can realize a large phase difference within a wide frequency range,besides,good amplitude and phase consistency over the entire band is also obtained.At the same time,the lens BFN has a smaller size than the traditional design method.The printed dipole antenna is adopted as the S-band array element,with its center frequency at 3.15 GHz.64 dipole elements is formed into an 8×8 triangular grid array.The designed S-band Rotman lens antenna can achieve a wide fractional bandwidth of 28.6% within 2.7GHz-3.6GHz for VSWR < 2.When the 11 beam ports of the Rotman lens antenna are sequentially excited,a very wide scanning range with a maximum beam pointing of approximately ±45° can be achieved.The X-band Rotman lens design method and structure,the number of the array element,and the array configuration are exactly the same as the S-band multi-beam antenna design.The only exception is,a wider impedance bandwidth is obtained by using the Vivaldi antenna as the radiator.The center frequency of the X-band multi-beam antenna is 9.9GHz.The achieved fractional impedance bandwidth for VSWR < 2 is about 40% for the Rotman lens antenna,and the final designed X-band multi-beam antenna can achieve a very-wide-angle scanning range with a maximum beam pointing of more than ±45°?...