Study On Dual-Mode Resonant 2-D Full-Wavelength Yagi-Uda Antennas

Compared with dipole antennas at the basic form,Yagi-Uda antennas have the advantages of high gain/directivity,easy to set up and low cost.Since invented in 1926,Yagi-Uda antennas have been extensively developed and presented.In order to improve the gain of Yagi-Uda antenna,the number of directors can be increased.In order to improve the bandwidth of Yagi-Uda antenna,the radius of radiator should be increased.In addition,sleeve-dipole antenna and the multi-mode theory can be introduced.It is always a challenge for Yagi-Uda antenna to realize both broadband and high gain.Recent studies show that compared with one-dimensional half-wavelength radiator,two-dimensional(2-D)full-wavelength radiator can not only realize wideband high-gain performance,but also maintain low cross-polarization performance within the beam.In this thesis,a2-D sectorial full-wavelength radiator is proposed to design and realize a wideband high-gain Yagi-Uda antenna with simple structure and compact size.1.The design process starts with a full-wavelength 2-D sectorial principal radiator,a fullwavelength sectorial director and a plane reflector.For the convenience of fabrication,the principal radiator and the director are designed on the PCB,and the center frequency is set at 2.4 GHz.Unlike traditional Yagi-Uda antennas,the principal radiator and the director are all full-wavelength designs to improve the directivity and gain.2.An improved Yagi-Uda antenna is designed.In order to determine the distance between the director and the principal radiator as well as the radius and flared angle of the director,a six-source model is developed: Six infinitesimal,electric current sources are sampled on the peripherals of the director and principal radiator,at the antinode and half-power point of the current distribution,respectively.The combined far field can be estimated to evaluate the basic radiation behavior.Through MATLAB simulation,when d is tuned to 0.024λ(d is the distance from principal radiator and director),the front-to-back ratio can be enhanced and the E-plane pattern can be narrowed down.Therefore,it is seen that a close separation of d between principal dipole and director may be beneficial for directivity enhancement for Yagi-Uda antenna designs.Unlike the conventional Yagi-Uda antenna with director separation varied from 0.1-wavelength to 0.3-wavelength,the separation can be remarkably reduced to 0.024λ in the case of 2-D,full-wavelength sectorial design.3.Finally,the described three-element Yagi-Uda antenna is designed and fabricated.Without loss of generality,many kinds of Yagi-Uda antennas are further designed,manufactured,and measured to verify the validity of the design approach.Through physical verification and HFSS simulation,the measured and simulated results of all antenna samples are relatively consistent,which proves the correctness of the six-source model.It is also verified that the antenna can realize both broadband and high gain design.This design method exhibits great practical application potential.It is expected to be applied in base station antenna.