Research On Tunable Antenna And Substrate-Integrated Magnetic Dipole

With the rapid development of wireless communication,the demand on integrating multiband and multiple wireless standards into a single wireless platform or systems is increasing.As the access interface for the signal transceiver in the communication system,antenna acts an important role in ensuring the quality of communications.Considering the portable and mobile trend of the terminal system,the high-integrated antenna with a small volume has become a common theme.In the situation of the increasingly scarce spectrum,the highperformance tunable antenna have significant effect on improving the spectral utilization efficiency.Thus,the study of the high-integrated tunable antenna is of great significance to the future development of wireless communication systems.In this thesis,the research of magnetic dipole and tunable antennas in recent years is reviewed and analyzed firstly.Then the performance improvement and functional design of tunable antenna based on planar structure are proposed.Furthermore,the substrate integration of magnetic dipole is established to construct the SIMD(Substrate Integrated Magnetic Dipole).Meanwhile,the performance defect is optimized to complement each other.At last,the tunable design is performed on the substrate integrated magnetic dipole and its frequency control scheme is analyzed based on the advantage of the magnetic dipole in the radiation direction diagram.For the tunable antenna section,the design and analysis of the discrete control for the operating frequency are carried out firstly.On this basis,a tunable antenna with the independent adjustable dual-band and the switchable single-band/dual-band is designed.Then,the function integration of tunable narrow single-band and broadband characteristics is realized based on the research of broadband antenna.The main research contents include:(1)A multi-band antenna based on the microstrip-line-fed wide-slot is presented.With the control from the angle of the Y-shaped microstrip line,the frequency responses is studied.The electromagnetic energy coupling between the different angle and equilateral triangle wide-slot is analyzed.Thus,a wide-slot antenna with controllable multi-band is realized.Furthermore,the varactor is adopted as the tunable device with improving the structure.A tunable antenna based on the equicrural triangle wide-slot,which is stimulated by asymmetric Y-shaped microstrip line,is achieved.Then,combining the asymmetric arms of Y-shaped microstrip line with the active devices loaded at the asymmetric positions,the perturbation of electromagnetic energy from the Y-shaped microstrip arms is analyzed and the compensation of the impedance matching from the varactors is presented.As a result,a tunable antenna with the tunable single-band,the independently tunable dual-band and the switchable singleband/dual-band is achieved.(2)First of all,The bandwidth characteristics of the antenna are studied based on composite right/left handed transmission line.The bandwidth enhancement is proposed from extremely narrow band to broadband.Then,an ultra wide band antenna based on the rectangular aperture,which is stimulated by an arrow-shaped microstrip line,is presented.Meanwhile,the coplanar waveguide feeding line is adopted to connect the arrow-shaped microstrip line.With the analysis of electromagnetic characteristics between arrow-shaped microstrip line and the rectangular aperture,the embedding and control for the stop band are designed.According to the surface current distribution of the antenna,two symmetric square apertures carved on the ground plane are proposed.Hence,the separation of the narrowband part and the broadband part from ultra broad band characteristics is achieved.On this basis,the loading positions of the tunable devices are confirmed through the analysis of the coupling field in the slot area.Simultaneously,the function of tunable narrow single-band is realized when the broadband characteristics remain based on the comprehensive control strategy of the varactors.For the substrate integrated magnetic dipole part,the design and analysis of radiation null compensation are carried out based on the blind points on the radiation patterns firstly.Then,the performance improvement and optimization of the isolation between two magnetic dipole antennas are presented.The detailed research contents include:(1)A planar magnetic dipole is constructed based on the way of substrate integration.Through the analysis of the equivalent magnetic currents on the aperture,the equivalent combined model of radiation pattern deriving from substrate integrated magnetic dipole is established.In order to tackle the radiation blind points,the orthogonal configuration of magnetic dipole is employed and two substrate integrated magnetic dipole antennas with advantage and defect complementing each other is achieved.As a result,there is no unwanted radiation null in all-side direction based on the way of null compensation and the analysis of radiation pattern.(2)In order to enhanace the isolation between two orthogonal magnetic dipole antennas,a HMSIW(Half-Mode Substrate Integrated waveguide)cavity is constructed through the orthogonal combination of magnetic dipole,which employs the metallized vias.With loading the DSS(Defected Surface Structure)on the surface of half-mode substrate integrated waveguide cavity,the high isolation between the antennas is realized.Moreover,the defected surface structure is composed of the HCSRR(Half Complementary Split Ring Resonator)slot loaded on the upper surface.Combining the design of the above two parts,the tunable characteristics based on the substrate integrated magnetic dipole are studied.Firstly,a defected surface structure,which is loaded half-elliptic slot on the upper surface of substrate integrated magnetic dipole,is presented.With the analysis of the electric field distribution on the substrate integrated magnetic dipole,the axial ratio of half-elliptic slot is confirmed.By loading the varactor at the short axis,a single-band tunable antenna based on the single substrate integrated magnetic dipole is designed.Furthermore,the dual pieces of back-to-back SIMD structures,which depend on the structural advantage of the substrate integrated magnetic dipole,is formed.Simultaneously,the half-elliptic slots with fixed axial ratio are adopted and the varactors are loaded at the short axises.Thus,the tunable antennas are presented.In addition,their positions of radiation patterns can be independent of the tunable structural switching.According to the analysis about the interactional mechanism of the reverse magnetic currents from the dipoles,the scheme of distancing the frequency points from each other is employed.Thus,the dualband independent tunable characteristic is achieved and the expansion of tunable range is realized.Simultaneously,the switching between frequency bands is compatible with the same azimuth of radiation pattern.