Design Of A Broadband Double-ridged Horn Antenna

With the rapid development of ultra-wideband?UWB?technology,because of its large capacity,ultra wideband,high rate,UWB antenna has been widely applied in the field of electromagnetic compatibility,electromagnetic measurement and ultra-wideband radar.Traditional horn antennas can cover a limited frequency range and is difficult to meet the requirements of UWB system.In order to obtain a wider working bandwidth,double-ridged horn antenna?DRHA?is formed by using the ridges as a part of structures for horn antennas.The cut-off frequency of the dominant mode(TE₁₀)is lower in waveguides or horn antennas,and the higher-mode's(TE₂₀)cut-off frequency become higher duo to the capacitive effective caused by ridges.DRHA are very attractive for electromagnetic compatibility testing and feeding reflector antenna due to the advantages of small size,high aperture efficiency and directivity.DRHAs have been used as standard antennas for a long time.However,only the E-plane and H-plane radiation patterns have been measured and analyzed,no attention has been paid to the 45°-plane and 3D patterns in the past.With the development of related research,it was found that the radiation patterns of conventional DRHAs cannot remain stable in the whole frequency band.The main lobes would begin to split and the gain would seriously decline when the frequency is above 12GH.In this paper,the development of broadband DRHAs is introduced.Also the design of DRHA is studied.Firstly,based on the basic theory of horn antenna and the ridge waveguide theory,a 2-18GHz DRHA is proposed in this paper.a DRHA with the operating band of 2-18 GHz is designed and simulated.The distortion of radiation pattern and the reduction of gain can be solved at high frequency by improving the ridge curve shape.The Bézier curve is used instead of the exponential type curve.And the feeding structure is also simplified.Secondly,the antenna is manufactured and tested according to the previous chapter.However,it is found that the measured results are very different from the simulation ones.Further analysis shows that the gap between the antenna structures,which is caused by fabrication tolerance and assembly error,leads to the deterioration of antenna performance.This problem is solved by extending the end of ridge into the short circuit board.Furthermore,the end structure of ridge is optimized,which can reduce the antenna size.The proposed antennas are processed and tested.The results show that the designed antenna has good radiation characteristics over the whole frequency band from 2 to 18GHz.The VSWR is less than 2 and the gain is stable in the high frequency band.Moreover,the existence possibility of gaps which may cause the deterioration of antenna performance are reduced,The proposed antenna is suitable for electromagnetic compatibility testing and the feed for reflector antennas.Finally,in order to reduce the weight of the antenna,a DRHA with open boundary is designed to operate in the band of 1-18 GHz.The ridge with linear gradient width is ultilized to realize miniaturization and improvement of horn section structure.The VSWR and radiation patterns are improved.