Design Of Broadband And Multi-band Antenna

Ultra-wideband(UWB)technology has attracted much attention and has been widely used in the fields of electronic communication,electromagnetic interference and radar detection.As an indispensable part of UWB system,broadband antenna is responsible for transmitting and receiving electromagnetic waves and interconverting them with radio frequency(RF)signals.With the continuous development of electronic information technology,people put forward the requirements of directivity,high gain,miniaturization of broadband antennas.In some special applications,such as multi-band seeker antenna system,it is difficult to meet the requirements only with single antenna and multi-band antenna needs to be constructed.While each antenna needs to satisfy its own index at its band,the layout of each antenna should be co-ordinated to prevent interference between each other.Based on this background,the design and research of broadband and multi-band antenna are carried out in this thesis.The work accomplished is as follows:1.The background and development of broadband antennas,especially the conical monopole antenna and Vivaldi antenna are introduced.On this basis,process of the design on these two kinds of antennas are introduced simply.2.Designing a broadband conical monopole antenna.Based on analyzing its structure and working principle,the design idea of beam control is put forward.By optimizing the size of conical monopole antenna and the shape of generatrix of the cone conductor and reflecting ground,a double-exponential conical monopole antenna covering 8-12 GHz is designed,and the standing wave ratio and pattern characteristics satisfying the anticipated requirements are obtained.3.Designing a Vivaldi array antenna.The design scheme of rotating the radiation opening of traditional Vivaldi antenna and configuring a new feeding structure is proposed.Compared with the feeding structure of microstrip line-slot line,it has the advantage of miniaturization.Then the antenna elements are copied and rotated around the central axis to form a six-element circular array,which can meet the requirement of omnidirectionality of the antenna at the specified angle of pitching.By loading microwave absorbing materials(MAMs)on the radiation element,the deterioration of standing wave caused by the coupling between the elements is greatly improved.Finally a one-six power divider is designed.Without increasing the transverse size,by making the widths of the first-order impedance transform line of the one-three power divider be no longer equal,the coupling effect caused by the connection of the one-two power divider and the one-three power divider can be improved.4.The Vivaldi array antenna is connected with the one-six power divider to form the low-frequency-band antenna covering 3-6GHz.At the same time,a dual-band antenna is constructed by coaxially arranging the conical monopole antenna and the Vivaldi array antenna.The measured results of the antennas show that the two pairs of antennas meet the requirements well.5.The method of miniaturization and high gain of the circularly polarized Vivaldi circular array antenna is discussed.The design of the beam control of conical monopole antenna and Vivaldi antenna,as well as the method of miniaturization and high gain of Vivaldi circular array antenna proposed in this thesis have certain engineering application value.