Research On Errors Of Time Domain Near-Field Antenna Measurement

With the gradually increasing of antenna performance,the requirements of the technology of antenna test is also gradually increasing.Antenna test technology is developing through the far field test to the frequency domain near field test,and ultimately to the time domain near field test.All test techniques need to go through theoretical theory,theoretical development,practical test validation and engineering application.Since the basic theory of time domain near field test had been proposed in 1994,the theoretical correction and the actual test system structures were completed in a few years,but due to the lack of systematic study of error terms,time domain near field test has been unable to enter the field of engineering application.The related research of test error has always been an important part of the test technology.As an example,the correction of the probe error of the near-field test in frequency domain ensures the test accuracy of the sidelobes,and the summary of the 18 errors make the interference terms clearly,guides the direction of improving the accuracy of the test.The uncertainty of results for the test system represents the test accuracy.For the near-field test of the time domain,while the researchers have had completed the test system and started to work,they also began to research on the errors.However,these studies are basically for one certain or few errors,they are isolated,scattered,lack of systematic,which resulting in only part of the test results errors,and they can not establish a perfect error system.The imperfect error system will lead to the failure of error estimation,which hinders the development of the near-field test to the engineering application stage.In order to fill the gaps in this part of the study,the error field of the near-field test in the time domain is studied by using the antenna near-field test as the research object.The work of this paper is to systematically study the error terms of the time domain antenna near-field plane test.Generation mechanism,the influence of the test result and the correction method or the value constraint condition of the unique error of time domain near field test are studied.The innovation in this paper is as follows:Firstly,the source of the near field test error term is research comprehensively.For the first time,the error term included in the time domain near field test is given.The 18 error terms included by frequency domain test are also included by time domain test,and the time domain unique error term is present: signal source stability error,time sampling length error,time sampling interval error and probe modulation error,the error of test results decrease from 1.2dB to 0.2dB while all the test errors are corrected;Secondly,a pure time domain correction method for signal source stability error is proposed for the first time.Due to the limitation of the excitation signal,the stability error of the signal source is usually corrected by the time-frequency domain method,and the correction of the pure time domain signal can not be carried out.This problem makes of the test results in the time domain near field test is shown with low accuracy.In this paper,arbitrary waveform generator is applied as the signal source,and the modulated Gaussian signal is used as the excitation signal.Simulation and test results verify the correctness of the pure time domain signal correction method that the amplitude error of first sidelobe level changed form 1.4dB to 0.3dB in S band and changed to 0.5dB in C band.Thirdly,a new method to analysis multiple reflection error and truncation error are proposed by using time domain signal.It is possible to estimate the multiple reflection signal between the probe and the antenna by measuring the time domain reflection signal on the port of the antenna.far field pattern of the multiple reflection signal is obtained,which provides a reference to analysis the influence of the multiple reflection signal on the test results.The time domain far field signal in the time domain near field test contains the reverse oscillation signal caused by sampling on the finite plane.By truncating the signal,it can effectively improve the confidence field of the far field pattern in the frequency domain.Fourthly,the definition of the modulation error of the probe is proposed and the mechanism of the error is studied.The mathematical expression of open rectangular waveguide probe modulation function is given,and the method modifying the probe modulation error by numerical calculation is proposed.results shows that amplitude error is less than 1% after the modulation error is corrected in simulation and less than 10% in test while SNR is only 10 dB.The feasibility of the modified method is verified by simulation.