Research On Miniaturized Wideband Vivaldi Antennas And Beam Scanning Arrays

With the increasing demands for portable and compact wireless communication devices,the antennas,for receiving and transmitting the electromagnetic wave,need to have broadband,miniaturization and beam scanning characteristics at the same time.Vivaldi antenna,widely used in indoor localization,medical imaging,phased array radars and other wireless communication systems,is an ultra-wideband traveling wave end-fire antenna with simple structure.However,the Vivaldi antenna has a large size and its array has a narrow beam scanning range.In this dissertation,the miniaturization and wide-angle beam scanning characteristics of the Vivaldi antenna are studied,and three main innovative research works are included.Firstly,a miniaturized maple-leaf antipodal Vivaldi antenna with high gain is proposed.A pair of radiating arms with maple-leaf edge shape is introduced to reduce the discontinuity of the surface current distribution at the radiating slot,thus the antenna gain is improved without increasing the antenna size.Two rows of symmetrical metallized vias are loaded on the inside edges of the exponentially slot to adjust the phase distribution of the electromagnetic wave,thus the beamwidth is broadened without decreasing the antenna gain.The measured results show that the impedance bandwidth of|S₁₁|<-10 d B is 5.2-40GHz,the maximum gain is 13.9 d Bi,and the antenna size is only 0.52?_0L×0.54?_0L×0.002?_0L(?_0L is the free-space wavelength at the lowest operating frequency).Secondly,a miniaturized half-mode?HM?Vivaldi antenna and array are proposed based on the mirror image theory.The HM-Vivaldi antenna consists of a modified radiating arm and two rows of metallized vias,which are equivalent as an electric wall.The induced current on the electric wall can replace the mirror image current of the radiating arm at its symmetrical position,thus the antenna size is reduced by almost half.A kind of ring-shaped metamaterial is introduced at the radiating slot to delay the phase of the electromagnetic wave and correct the beam direction of the antenna.The measured results show that the impedance bandwidth of|S₁₁|<-10 d B is 5.3-40 GHz,the maximum gain is 11 d Bi,and the antenna size is only 0.35?_0L×0.54?_0L×0.009?_0L.A four-element HM-Vivaldi array is designed by arranging the element in mirror image.The vertical E-field components of the antenna along the substrate can be canceled,so the cross-polarization is reduced and the pattern asymmetry of the Vivaldi antenna is eliminated.The simulated results show that the cross-polarization of the array is lower than-55 d B over 4-15 GHz band,and the main beams in the E-and H-planes are symmetrical.Thirdly,two Vivaldi antenna arrays with wide-angle beam scanning and compact size are proposed.First,a frequency beam scanning array is presented based on the HM-Vivaldi antenna.The array elements are excited in series along the microstrip transmission line.The various frequencies induce phase difference,so the beam scanning performance is achieved.The Spoof Surface Plasmon Polariton?SSPP?structure is loaded on one side of the transmission line to expand the beam scanning range of the array.The simulated results show that the impedance bandwidth of|S₁₁|<-10 d B is 6-15 GHz,in which the beam scanning range is-40°?87°with the maximum gain of 14.1 d Bi.Second,a millimeter wave Vivaldi beam scanning array is presented based on the tight coupling theory.The beam scanning performance is achieved by the different phases at the excitation ports of radiating elements.The surface current path of the array is lengthened by the tight coupling between the adjacent radiation elements,so the impedance bandwidth and the beam scanning range are extended.The simulated results show that the impedance bandwidth of|S₁₁|<-10 d B is22.4-30 GHz.the maximum gain is 11.9 d Bi.A wide beam-scanning ranges of 150°in the E-plane can be achieved at each frequency point over the band with the array spacing being only 0.28?_0L.