A Design Of UWB Feed Based On Logarithmic Period Antenna Theory

The decade ultra-wideband radio telescope currently being developed has several feed technologies,such as Quad-Ridged Horn Feed,improved Quadruple-Ridged Flared Horn Feed,Sinuous Feed,Quasi-Self-Complementary Antenna and Eleven Feed.The Quad-Ridged Horn Feed is an all-metal structure that can be directly connected to a standard 50? coaxial output port.Besides that,it can flexibly control the beam width by changing the Flared angle.But its beam width and phase center change with frequency,which results in a low aperture efficiency.Compared with the original Quad-Ridged Horn Feed,the improved Quadruple-Ridged Flared Horn has wider and more stable beamwidth.,but the phase center varies with frequency.Both the Sinuous Feed and the Quasi-Self-Complementary Antenna are non-planar broadband log-periodic dual-polarization antennas,but the beamwidths of the two feeds vary with frequency.Yet the hardware has not been implemented beyond 4 GHz.Compared with the other feeds,Eleven Feed has received more and more attention in recent years due to its advantages such as ultra-wideband performance,stable beamwidth and phase center as well as small dimension.Based on log-periodic antenna and folded dipole theory,an ultra-wideband Eleven Feed was designed according to the requirement of the project.The Eleven Feed with ultra-wideband passive balun and ultra-wideband power combiner was simulated using HFSS software.Then the antenna was fabricated and measured.The measurement results showed that all parts met the requirements of the project.The design of an ultra-wideband Eleven antenna cascades folded dipoles in the form of log-periodic arrays.The design of an ultra-wideband Eleven Feed is based on the theory of the log-periodic antenna and uses the form of a folded dipole.During the development of the Eleven Feed,in order to improve the BOR efficiency of the antenna,a rotationally symmetrical model needs to be constructed.In this design process,a series of hollow-cylindrical sections with similar log-period ratios and similar tile structures were used.By removing the intersections between them and the metal patches,the projection of the folded dipole lobes on the reflect plane is constructed to be circular to ensure that the antenna is strictly rotationally symmetric.In the simulation process,the performance of the frequencies paid attention to in the frequency band can be adjusted by changing the tilt angle between the dipole and the reflect plane,the opening angle of the dipole,the size of the dipole feeding gap,and the logarithmic cycle scale factor.In the system design of the Eleven Feed,the power combiner design utilized the Klopfenstein progressive line technology,metal cavity package,and pin gap waveguide technology.The Klopfenstein-type asymptotic line makes the power combining perform well in the whole operating band.The design of the metal cavity shielded the resonance in the low-frequency band,and the design of the pin-type array shielded the resonance in the high-frequency band.After that,the ultra-wideband passive balun was designed to feed the Eleven Antenna.The four UWB baluns connected directly to four corresponding pairs of parallel lines,and the four pairs of parallel lines connected to the dipole pedals through four vias in the floor.Because the two opposite dipoles were the key components of one same polarization,the two pairs of baluns in this design were located orthogonally to achieve a compact dual-polarized feed.The results at frequency points in the operating band showed that the UWB baluns can meet the requirements.The Eleven Feed of this design still has possibilities for improvement.First,when the parameters of the Eleven Feed were designed to adjust the beamwidth of the antenna,many parameters can be adjusted,and these parameters were often triggered by the whole body and needed to be adjusted jointly.For example,when changing the angle between the dipole and the xoy plane,the height of each folded dipole arm to the floor is also changing,which would make the optimization process cumbersome and complicated.In next-generation improved design,the current distribution on the folded dipole pedals should be used to represent the far-field function.Through modeling in MATLAB,the Eleven beamwidth could be optimized by algorithm.The power combiner performance was good in this design but it was required that its size was still not small enough,and there was no comparison between the asymptotes of different functions in this paper.In the later work,it is necessary to pay attention to the differences between these different asymptotes.The UWB passive balun designed this time is a linear asymptotic balun,and the result at the frequency point within the operating band could meet the requirements.However,by optimizing the asymptote,the size of the balun could be further reduced,thereby making the overall structure of the antenna more compact.