Research On Circularly Polarized Antennas And Arrays Of Satellite Communication And Navigation Systems

With the development of satellite navigation and communication technology,the demand of performance of electronic equipment is becoming higher and stricter.Meanwhile,the system of communication and navigation becomes miniaturized,integrated,multi-frequency and broadband.In order to adapt to the tendency,a large amount of literature is delivered to study bandwidth and beamwidth broadening,miniaturization and other techniques of antennas.In combination of the research highlight of antenna and requirement of project,this thesis gives effort on the techniques of antenna integration,miniaturization,bandwidth broadening and beam forming.Based on the antenna theory,kinds of circularly polarized antenna elements and arrays are designed.The author's major work can be summarized as the following parts:1.Based on the requirement of the communication system in application platform,three groups of widebeam circularly polarized composite antennas,which can cover six bands,are designed.Firstly,the polarization mode of each frequency band and the problem of radiation occlusion are analyzed to determine the combination and layout of the antennas.Then,according to the indications of the UHF?Ultra High Frequency?satellite antenna and the installation environment,both advantages and disadvantages are compared between the dual-frequency nested quadrifilar helix antenna and dual-frequency coplanar bifilar helix antenna.The former structure is more complex,however,the radiation pattern shows better uniformity in each direction.As a result,the dual-frequency nested quadrifilar helix antenna is chosen as the radiation element,and two double-layer miniaturized feed-nets are designed as the feeding network of the element.Then a group of L and S bands of composite antennas are designed.Both of them are left-handed circularly polarized.Due to the low profile property,the distributed antennas are chosen as the radiation element,which placed at upper and lower position,respectively.However,the beamwidth shows narrow.Thus,the metal support of the upper antenna is reshaped to the cone type,which is expected to widen the beamwidth.Finally,to achieve wide band operation,an antenna combined the conformal helix antenna and Archimedes helix antenna is used as the radiator,and a wideband exponential gradient Balun is integrated to the antenna.In summary,the VSWRs?voltage standing wave ratio?of antennas keep below 2 and the gains above 25°keep above-5 dBic over the six operating bands.2.According to different navigation systems and application platforms,three kinds of circularly polarized antennas with different performances are designed.Firstly,a wide-beam circularly polarized antenna which can be employed to Beidou B3 band is designed.It utilizes the dipole arranged in parallel.By adjusting the distance between the elements,the antenna can obtain a 3-dB axial ratio beamwidth of 162°.Meanwhile,through bending the arms of dipoles,the HPBW?half power beamwidth?of the antenna is broadened to 114°.Secondly,a circularly polarized distributed antenna with high efficiency and low profile antenna is designed.The radiator of the antenna is consisted of four square metal plates,which are loaded with shorting-pins.The feeding network is a series-fed power divider and the radiation efficiency reaches above 96.5%.The 3 dB axial ratio bandwidth is 22.8%.Finally,a miniaturized circularly polarized antenna based on electromagnetic coupling feed is designed to cover Beidou B3 band.By utilizing of the virtual shorting,the miniaturization and the broadening of the bandwidth are realized.The final size is reduced to0.11?₀x0.11?₀x0.068?₀.3.Two 2x2 wideband circularly polarized antenna arrays are designed for vehicles.Firstly,the technology of electromagnetic coupling feeding and rotary layout are studied and applied to the antenna element and array.Then,a 2x2 antenna array is designed.The antenna element adopts the wideband octagon dipole.The swallow-tail feeder is adopted as the electromagnetic coupling feeding patch.The impedance bandwidth of this antenna array is widened to 57.1%.Axis ratio is less than 0.75 dB over the entire impedance band.Then,a high-gain 2x2 antenna array is designed.The element utilizes a wideband elliptical dipole and a harpoon-shaped feeding patch.In order to increase the gain,a ring reflector is loaded on the periphery of the array.And the bandwidth of 10 dBic gain reaches to 55.2%.4.According to the requirement of satellite antennas,the beam-forming technique of the antenna array is studied.Firstly,a wideband circularly polarized antenna is designed to cover the three operating bands of the Galileo navigation system.Secondly,an antenna array is synthesized by the PSO?Particle swarm optimization?and GA?Genetic Algorithm mixing algorithm?.The required radiation pattern is achieved.Thirdly,a wideband phase-shift network is designed.And the prototype of the antenna array is manufactured and measured.The results prove the feasibility of the technique of array synthesis.