Planar Endfire Circularly Polarized Antennas And Arrays

As the development of the modern wireless system,the circularly polarized(CP)antennas have attracted considerable attentions in the fields like communication,radar detection and navigation,since they can avoid the polarization mismatch,suppress the multipath reflection and not subject to the Faraday rotation effect.Meanwhile,in practical applications,the planar endfire antennas are highly desirable to satisfy demands on the manufacturing,integration and aerodynamic characteristics.Faced with the above-mentioned facts,systematic studies on the theory and techniques of the planar endfire CP antennas have been conducted in this thesis,where array technologies have also been applied to produce various required radiation patterns.Specifically,the full thesis can be divided into the following four parts.1.Based on the duality of electricity and magnetism,the planar endfire antennas with circularly polarized radiation have been designed using the substrate integrated waveguide technology.The concept is the superposition of two closely spaced complementary dipoles.Comprehensive comparison has been made between different implementations of the dipole antennas.The amplitude and phase relations between two complementary dipoles can be effectively tuned by introducing the double-sided slot-coupled line and the parallel strip line.With the help of the equivalent models,the operation mechanism and design guidelines of the proposed endfire CP antennas were obtained.A method of independent tuning was also developed,which makes it possible for the fast design and the reconfigurable polarization.Finally,two different planar endfire CP antennas were successfully evaluated and the corresponding theories were verified.2.A single-layer bidirectional antenna which provides CP radiation of the same sense in both of the hemispheres has been designed and evaluated.The concept is the combination of two identical endfire CP antenna elements in the back-to-back configuration.The design of each element is based on the superposition of two closely-spaced complementary dipoles.The formulation of the bidirectional same-sensed pattern was clearly explained with the theory of two-element array.A single coaxial-probe-fed technique was developed by introducing an open window on the perfect electric conductor(PEC)wall shared by the two antenna elements,thus an additional power divider can be ignored.The operation mechanism of the single feeding for replacing the dual-feeding was given with the analysis of the equivalent boundary conditions,and the principle of the impedance matching was also provided accordingly.Symmetries in both the antenna structure and the feeding typology ensure the consistency of radiations in two different directions.3.A low-profile CP antenna with omnidirectional radiation has been designed and evaluated.The concept is the combination of multiple identical endfire CP antenna elements in a circular array configuration.By comparing performances at different design stages,strategies for improving the omnidirectivity of the proposed antenna were presented.Detailed analysis on the eventually utilized sector-shaped endfire CP antenna element was made,which helps to understand its operation mechanism.Moreover,influences of the number of the circularly arranged elements on the omnidirectivity and the antenna size were investigated.Benefiting from the adoption of the shorted via in each sector,the proposed omnidirectional antenna can be excited in its structural center with a single coaxial probe.The final design results indicate that good omnidirectivity in the azimuth plane and a wide coverage in the elevation plane can be obtained within the target frequency band.4.A single-layer single-fed endfire antenna with circular polarization and unidirectional radiation has been designed,which has a relatively high gain and an acceptable front to back ratio.The idea is based on two complementary Yagi-Uda arrays,including an electric dipole Yagi-Uda array and a magnetic dipole Yagi-Uda array.When comparing with the classic linearly polarized Yagi-Uda antennas,two new problems were arisen.First,interactions between director,driven element and reflector of two complementary Yagi-Uda arrays should be considered.Second,a series feeding technique with the ability to precisely distribute the power to each radiator should be developed.Afterwards,the one-dimensional fixed-beam array of the proposed unidirectional endfire CP antenna was investigated.A planar feeding network was proposed to ensure the array can be printed on a single-layer substrate.The antenna arraying lays the basis for putting forward the solutions in conformal applications and the beam-scanning.