| As modern communication scenes are more and more complex,the antenna device located at the front end of the radio frequency system is of higher requirements.Antennas with conventional performances have difficulty to meet these requirements.Beam-scanning antenna has the advantages of multi-beam coverage capability and flexibly controllable radiation beam.When the position of the communication equipment changes dynamically,the beam-scanning antenna can real-time and flexible adjustment of the radiation beam to realize the communication with multiple target positions.Leaky-wave antenna is one typical kind of traveling-wave antenna.Its frequency-dependence beam-scanning function depends on the unique dispersion characteristics of the transmission line loaded with radiating elements.Leaky-wave antenna owns the distinguishing features of simple structure,high gain and continuous beam scanning.So it attracts much attention from many related scholars inside and outside the country.However,traditional leaky-wave antenna designs often suffer from the open stopband problem,changeless circular polarization radiation realization means,and low radiation efficiency.So it is an important research topic in beam-scanning antennas to improve leaky-wave antennas’working performances in all directions and excavate leaky-wave antennas’potential.However,for some communication systems with limited bandwidth resource and size,it is no longer suitable to utilize the long array length and wide bandwidth leaky-wave antenna for beam-scanning function.Pattern-reconfigurable antenna can realize several beam-switching states within a common operation band.It reconfigures different resonance modes in one shared radiation aperture by mechanical,electronic and special material medium adjustment conditions,thus creating different radiation responses in the far-field.Pattern-reconfigurable antenna extends great design freedom and has the potential to realize a very wide signal coverage range.However,conventional pattern-reconfigurable designs usually face different problems,such as excessive size occupation and limited reconfiguration diversity.This dissertation is along the main research line of leaky-wave antenna and pattern-reconfigurable antenna to realize the beam-scanning function.It in-depth studies of different radiation beam controlling schemes based on the two types of antennas.It focuses on solving the main problems among the two types of antennas and brings the two beam-scanning antennas’superiority into full play.There are mainly includes four parts of research work in this dissertation:1.Research on highly integrated circular polarization microstrip leaky-wave antenna.The microstrip type is one kind of common transmission line.Microstrip antenna can easily integrate with active circuits.Microstrip leaky-wave antennas hold the advantages of the microstrip structure,but the circular polarization scanning ranges of conventional microstrip leaky-wave antennas are usually very limited due to their inherent narrow-band effect.To address this problem,two novel circular polarization leaky-wave antennas based on meandering strip transmission lines are proposed.In the two designs,coplanar equivalent polarizer structure and structural modification of the strip transmission line influences on the circular polarization radiation characteristics are investigated respectively.Using the two methods,the two orthogonal polarization components for generating circular polarization radiation can be flexibly and independently controlled,thus achieving the circular polarization scanning range extension.2.Research on high radiation efficiency circular polarization leaky-wave antenna.The dielectric resonator is innovatively loaded on the meandering strip transmission line and the half-mode substrate integrated waveguide transmission line,respectively.The transmission line structure breakthroughs are to meet high gain,long-distance communication and compact size requirements.Two novel composite structure-based circular polarization leaky-wave antennas are proposed.Firstly,the feeding mechanisms of the two transmission lines for dielectric resonators are analyzed.Based on the effective excitation of dielectric resonator,a pair of orthogonal polarization components are generated by the composite structures,thus leading to good circular polarization radiation performance.Meanwhile,the three-dimensional structural excited dielectric resonator extends the radiation aperture in the vertical plane,which can more efficiently convert the energy in transmission structure into the radiation energy in far-field.Compared with the same-length conventional transmission line arrays,the radiation efficiencies of the two composite structure-based leaky-wave antennas are improved by 26.4%and 51.7%,respectively.3.Research on pattern-reconfigurable antenna with stable radiation states.Firstly,an omnidirectional folded dipole array as an assisted antenna is proposed.By etching interdigital capacitance gaps,a stable and specific phase difference between the equivalent radiation elements is obtained.This phase difference value is analyzed in detail.Then based on the phase difference in the assisted antenna,a pattern-reconfigurable antenna design with stable reconfiguration radiation responses is proposed.Two reconfigurable parasitic strips are utilized to construct different equivalent radiation element arrays and get corresponding radiation beam responses.The final design realizes two endfire radiation modes that point to opposite directions and one omnidirectional radiation mode.4.Research on pattern-reconfigurable antenna with diverse radiation states.It is verified that one pair of orthogonal and electromagnetic complementary radiation sources can create a highly directional radiation response.By utilizing the single-port composite structure of monopole and vertical split ring resonator,a pattern-reconfigurable antenna with eight different radiation states is proposed.Four PIN diodes embedded in the feeding network can flexibly and independently control the four complementary source pairs’resonance states.Through different combinations of resonance states,eight different directional radiation beams are synthesized,and the eight radiation beams cover one 360~°plane range. |
