Study On Wideband Backfire Antenna With Nearly Equal E-/H-Plane Patterns

A lot of attention has been attracted since the invention of backfire antenna in the 1960 s.In order to improve the impedance bandwidth of the backfire antenna,the primary radiator and primary reflector of the backfire antenna can be optimized and multi-mode resonance can be introduced.In addition,by optimizing the primary reflector of the backfire antenna,the nearly equal E-/H-plane patterns can be can be achieved.However,how to simultaneously realize the broadband and nearly equal E-/H-plane patterns of the backfire antenna has always been a great challenge.Recent studies have found that compared with one-dimensional radiator,two-dimensional radiator can not only bring broadband performance,but also maintain low cross polarization performance in the whole beamwidth.At the same time,the rectangular patch with cornered angle as the primary reflector of the backfire antenna can effectively adjust the half-power beam width of E-and H-plane,so as to achieve nearly equal E-/H-plane patterns.In this thesis,based on the theory of multi-mode resonance,a backfire antenna with simple structure,broadband,nearly equal E-/H-plane patterns and inverse taper radiation patterns at high frequency is designed.On this basis,a backfire antenna which can realize nearly equal E-/H-plane patterns in all frequency bands is completed.Finally,a dual polarization antenna is designed based on the first backfire antenna.The main contributions are as follows:1.The design process starts with a 1.5-wavelength two-dimensional sector primary radiator,a primary reflector with cornered angle and a circular secondary reflector.Different from the traditional backfire antenna,the primary radiator is designed with a 1.5-wavelength two-dimensional sector dipole.It can excite more modes,and the excited modes are perturbed together by introducing a mode disturbance device,so as to achieve broadband characteristics.The primary reflector is a rectangular patch with cornered angle,which is designed to achieve nearly equal E-/H-plane patterns.The backfire antenna at high frequency,due to the full excitation of high-order mode,presents the inverse taper radiation patterns,which can effectively provide sufficient edge illumination level,thus overcoming the inherent defects of common parabolic reflector antenna system due to the narrowing of high frequency beam and insufficient edge illumination,so that the parabolic reflector antenna system can obtain more uniform aperture field distribution in the wideband range.This backfire antenna design method has great potential in practical application and can be used as the feed of parabolic antenna in the future.2.The backfire antenna with a 1.5-wavelength 2-D sectorial dipole as the primary radiator has broadband,nearly equal E-/H-plane patterns and inverse taper radiation patterns at high frequency,but its bandwidth to achieve nearly equal E-/H-plane patterns is narrow.Therefore,an antenna structure that can achieve nearly equal E-/H-plane patterns in a relatively wide bandwidth needs to be designed.The backfire antenna with 1.5-wavelength 2-D sectorial dipole as the primary radiator fully excites the fifth-order mode,resulting in dispersion phenomenon at high frequency,so its equal E-/H-plane bandwidth is narrow.Therefore,we choose a full wavelength 2-D sectorial dipole as the primary radiator to avoid exciting the fifth-order mode of the antenna.Finally,the method of using the full-wavelength sector dipole with a center angle of 270 ° as the primary radiator of the backfire antenna is adopted.It can realize nearly equal E-/H-plane patterns in the whole impedance bandwidth.3.After completing the design of backfire antenna with broadband and nearly equal E-/H-plane radiation patterns,a dual-polarized backfire antenna is fabricated by placing two backfire antennas with 1.5-wavelength sectorial dipole orthogonally.The antenna can achieve dual-polarization characteristics while having the performance of the aforementioned backfire antenna and high degree of isolation.It has been verified that the dual-polarization antenna shows excellent performance and has a great application prospect in the base station antenna.