Design Of Miniaturized Antennas Loaded With Slow-wave Structures

With the enhancement of modern wireless communication system,lead-in correspondence equipments are widely intergrated in various devices.The horn antenna is usually used in radar communication and test plateform owing to its simple structure,large power capacity,stable radiation pattern and high directivity.Whereras,the huge size of conventional horn antenna constraints its application in the confined space.Thus,it is of important theoritical significance and practical engineering value for the researhers to carry out the study on the technique of horn-antenna miniaturization,especially opening up new direction for horn-antenna miniaturization.Based on the literature synthesis of recent approaches related to horn antennas,the theory of the radiation of the horn antenna is analyzed and verified with math software MATLAB in this paper.Furthermore,the basic theory of slow-wave structures(SWS)and the analysis methodology of capacitance-enhanced slow-wave structures are simply discussed.The main contents and contributions of this dissertation are as follows:The approach to employ SWS to improve the deterioration of the high sidelobe pattern of miniaturized horn is proposed.First,slow-wave effect and field-concentration effect are studied under different parameters of the slow-wave unit such as height,side length and shape of the SWS.The equivalent circuit model of the units of the corrugated waveguide is proposed.Besides,the stopband characteristics of the SWS at the upper edge of the frequency band is analyzed.Conventional miniaturized large H-plane horn antennas suffer from high sidelobes and decreased gain because of non-uniform phase caused by the decrease in longitudinal direction.The introduced SWS,formed by four pairs of rectangular blocks hidden inside the flared region,are able to produce slow-wave effect to realize a uniform phase and a tapered magnitude distributions of the electric fields on the aperture.By analyzing the effects of height of the metal blocks and the distance between metal blocks and aperture on the radiation pattern and impedance bandwidth along with optimizing the height and position of the coaxial probe in the coaxial-waveguide converter,a shortened horn antenna with supressed low sidelobes covering 10.5-15 GHz(relative bandwidth is 35%)is designed.Compared with the unloaded short horn antenna,the side lobe level of the radiation pattern in the whole frequency band is reduced to-25 dB.Compared with the optimum horn antenna,the longitudinal size of the miniaturized horn is reduced by 52.9%,and the average gain level in the whole frequency band is comparable to the optimual one.The approach to miniaturize horn antenna with SWS is presented.Based on the slow-wave effect of SWS,the phase error of electric field on aperture of the longitudinally miniaturized horn antenna could be corrected by loading metal blocks of different heights on the inner surface of H plane.On the basis of the above working mechanism,a miniaturized horn antenna loaded with SWS I is designed.Compared with the original antenna,the phase distribution of electric field at the horn aperture is more uniform.In order to further improve the magnitude distribution of electromagnetic field on the horn antenna aperture,a miniturized horn antenna loaded with SWS ? is further designed by optimizing the height of metal blocks in the midline of H-plane according to the concentration effect of SWS.Finally,by adjusting the height of the metal blocks near the horn mouth and the throat,the impedance matching in the working frequency band is improved.A miniaturized horn antenna loaded with SWS ? is finally obtained.The miniturized horn antenna loaded with SWS ? is processed and tested,and the measured results are in good agreement with the simulated one,confirming the feasibility of the method of horn-antenna miniaturization via loading SWS.In contrast with the original horn antenna,the horn antenna loaded with SWS ? reduces the longitudinal size by 33.3%,increases the gain by 1.7 dBi on average,and reaches a maximum radiation efficiency of80.7% in the operating band of 10.5-14.5 GHz(relative bandwidth is 32%).