Research On Phaseless Near-Field Antenna Measurement And Diagnoses Of Aperture

Near-field antenna measurements use a scanning frame system to collect tangential complex electric field information on a scanning plane(plane,column or sphere)in the near-field region(Fresnel zone)of the antenna radiation.And then calculate the far-field radiation information by means of spectral expansion.The electronic information industry is developing rapidly,and the frequency of antennas is increasing in order to meet the application requirements.Limited scanning rack positioning accuracy,RF transceiver stability,and so on lead to inaccurate phase measurements of high frequency antennas.The requirement to accurately measure the phase of high frequency antennas places extremely high demands on the measurement system.To address the problem of inaccurate phase measurement of high frequency antennas,the phaseless near-field antenna measurement is proposed.This method does not require phase information and uses only the near-field amplitude to achieve phase reduction by means of a phase reduction algorithm.This enables highly reliable near-field measurements of high frequency antennas.Achieving deep space exploration is a strategic goal for all major countries and relies heavily on large reflector antennas.With the increasing aperture and frequency of large reflector antennas,the surface accuracy diagnosis methods are being explored to meet the increasing application requirements.This thesis attempted to apply the phaseless near-field antenna measurement to the large reflector antenna surface accuracy diagnosis,trying to provide a new solution for the measurement of large reflector antennas.Firstly,this thesis introduced the research background and significance of phaseless nearfield antenna measurement and large reflector antenna surface accuracy diagnosis.And this thesis described the research status of phase reduction algorithm and large reflector antenna surface accuracy diagnosis.Then,this thesis analyzed the principle of phase reduction and develops a dual-plane based phaseless near-field antenna measurement technique.This technique performs phase reduction by collecting two sets of planar amplitudes in the near-field region of the antenna.The phase reduction process is as follows: the initial iterative phase is first generated using Particle Swarm Optimization(PSO),and this thesis innovatively introduces parallel computing into PSO to greatly accelerate the computational process.The initial iterative phase is then used as the input to the Iterate Fourier transform(IFT)algorithm to continue refining the phase reduction.After the convergence accuracy of the IFT algorithm has stabilized,a random phase is finally added to keep it converging.This solved the problem of IFT algorithms falling into local optima and further improves phase reduction accuracy.In order to verify the effectiveness of the phase reduction algorithm,three antennas are simulated in this thesis,and the final results showed the superiority.Besides,the robustness of the phaseless near-field antenna measurement to position errors is then analysed.Finally,for the purpose of aperture field diagnosis,three near-field to aperture-field transformation algorithms are presented in this thesis.For large reflector antennas,the geometric relationship of reflector phase deformation is analysed in detail,and the study of large reflector antenna shape accuracy diagnosis is carried out.Based on the phase-reduction algorithm and the near-field to aperture-field transformation algorithms owing near-field holography,simulations and measurements are carried out to validate the model of the reflector antenna.The final results showed the effectiveness of the phaseless near-field antenna measurement applied to the large reflector antenna shape accuracy diagnosis.And this thesis analyzed the sources of error in the method.