The Designs Of High-gain And Ultrawide Band Antipodal Vivaldi Antenna And Its Array

With the rapid development of electronic countermeasures,ultra-wideband communication and other fields,the electronic system has wider and wider bandwidth and higher and higher gain requirements for antennas.Vivaldi antenna,as one of the typical wideband antennas,has received sustained attention since its advent in 1970.Vivaldi antenna has been widely used in radio astronomy,medical imaging and broadband measurement systems.But,the end-fire gain of conventional antipodal Vivaldi antenna(CAVA)is usually unstable within a wide frequency band,Especially,the main beam of CAVA is normally tilted and splited at higher frequencies,resulting in decrease of the end-fire gain.These inherent problems will seriously restrict the application scenarios of CAVA.In order to improve the performance of Vivaldi antenna,the specific research contents of this thesis are as follows:Firstly,in the third chapter,a modified antipodal Vivaldi antenna with a periodic slit edge and a three-layer trapezoid-shaped dielectric lens(PSEAVA-TDL)is proposed.The lower cut-off frequency limitation is extended without changing the overall dimensions of the CAVA and the radiation performance is improved.At 4 GHz and 16 GHz,the end-fire gain of the antenna increased by 2.1 dB and 7 dB compared to CAVA respectively.The PSEAVA-TDL possesses stable radiation characteristics in a wide frequency range.In the fourth chapter,the phase shift characteristics of the dielectric element to the electromagnetic wave are analyzed,and in here,a phase compensation dielectric lens(PCDL)is designed taking into account the actual phase error at the CAVA5 s aperture to correct inherent problems of CAVA,called wideband near-field dielectric lens.The detailed analysis,design and discussion for CAVA with the proposed PCDL are performed.The effect of multilayer dielectric lens on the impedance and radiation properties of CAVA was further studied.Finally,the number of layers of dielectric lens was selected as 7.CAVA loaded with 7-layer dielectric lens(CAVA-SPCDL)was slightly mismatched in the low frequency band,which was overcome by loading a periodic slit edge.The CAVA,CAVA with seven-layer PCDL and periodic slit edge(PSEAVA-SPCDL)are fabricated and tested,The PSEAVA-SPCDL provides a gain variation of 7.9-14.1 dB,which leads to 2.2-9.5 dB gain enhancement compared to CAVA.It also exhibits stable radiation patterns with narrower half power beam width,and higher front-to-back ratio and lower sidelobe level inboth the E-and H-plane comparedto the CAVA.In chapter 5,two modified structures are proposed to eliminate the gain mutation point of the AVA array.Finally,the second modified structure loaded metamaterial which composed of parallel line unit cell,and the gain of the array is improved.The two improved structures also reduce the cross-polarization level of far-field radiation to a large extent.In summary,this thesis improves the characteristics of the conventional antipodal Vivaldi antenna by using the methods of corrugated loading,dielectric lens loading and metamaterial loading,The research results have important application value.