Design Of Widebeam And Cross-shaped Circularly Polarized Tapered Slot Antennas

The rapid development of wireless technology brings opportunities and challenges to antenna technology.Wideband,broad beamwidth,and circular polarization have became the focus of antenna design.Tapered slot antennas(TSAs)are widely applied to wideband wireless systems due to their wide frequency bandwidth and simple structure.However,the beamwidth in E-plane and H-plane of the traditional TSAs are not equal and varie significantly with frequency.So it is difficut to design a wideband TSA which has wide enough half power beamwidth(HPBW)in both E-plane and H-plane.Circularly polarized(CP)antennas not only have good immunity to multipath effect and polarization mismatch,but also can obtain larger communication capacity compared with linearly polarized antennas under the same conditions,so they have high practical values.However,the design of broadband CP antenna is difficult because of the fact that the working bandwidth of CP antenna is limited by both impedance bandwidth and axial ratio(AR)bandwidth.TSAs are suitable for designing wideband CP antennas by orthogonal placement due to their broad impedance bandwidth and high polarization purity.Based on actual project requirements,broad beamwidth and cross-shaped CP linear TSAs(LTSAs)are studied in this thesis.The main contributions of this thesis are as follows:1.Loading techniques which can widen beamwidth and suppress backward radiation of LTSAs are studied.First of all,by studying the effect of different loading structures on the HPBW of LTSAs,a wideband LTSA with broad beamwidth for human physical signs monitor application(Ant.1)is designed.The simulated and measured results indicate that a 10 d B return loss bandwidth of 51.7%(4.3-7.3 GHz)and a radiation pattern bandwiddth of 40.74%(4.3-6.5 GHz)are obtained.In the radiation pattern band,the HPBW in E-plane and H-plane of the antenna are more than 105° which can meet the project requirements.Then,a wideband LTSA with broad beamwidth and enhanced front-to-back ratio(Ant.2)is designed.Ant.2 inherits the loading structures used by the Ant.1 and makes some appropriate improvements.In the working frequency band,the backward radiation of the antenna can be obviously suppressed by loading chamfering,non-metallized through holes and inverted ?-shaped grooves.The antenna is manufactured and measured.The measured results show that,a-10 d B reflaction coefficient bandwidth of 51.7%(4.3-7.3 GHz)and a radiation pattern bandwiddth of 40.74%(4.3-6.5 GHz)are obtained.In the radiation pattern band,the HPBW in both E-plane and H-plane of the antenna is more than 100° and a moderately high average FBR(AFBR)about 19 d B is obtained.2.The methods of realizing wideband and circluar polarization based on LTSAs are studied.Taking wideband,low cost,high integration and small shielding as goals,a cross-shaped wideband CP LTSA is designed.Firstly,a cross-shaped dual polarized antenna is designed based on the microstrip-fed LTSA.Two complementary semi-ring structures are designed to avoid short connection between buluns when the antenna units are plaecd orthogonally.Then,a cross-shaped feed network is designed.The feed network is used to provide two equal amplitude excitation signals with 90 degrees phase difference for the cross-shaped dual polarized LTSA to realize circular polarization.In order to achieve integration,the feed network is divided into two parts and integrated with the LTSA units.Finally,loading technology is applied to improve radiation performance of the antenna.The simulated and tested results demonstrate that not only the HPBW can be widened by loading,but the backward radiation of the antenna can also be suppressed.A wide CP bandwidth of 92.5%(3.6-9.8 GHz)is obtained by the loaded cross-shaped CP LTSA.