Study Of The Near-Field Antenna Measurement Method

Antenna measurement is a very important part of antenna design,but due to the development of modern communication technology,the accuracy requirements of the antenna are getting higher and higher,and this high precision antenna has high requirements for the measurement environment,especially in temperature and humidity.The traditional far-field measurement method is difficult to meet the requirements.In addition,the far-field test can not realize the measurement of large array antennas due to the limitation of site distance.Therefore,near-field measurement has become the focus of current attention.Near-field measurement refers to scanning a specific surface in the radiation near-field region of the antenna to be measured through a probe with known performance to obtain the data on the measurement surface.Then,the far-field data and aperture field information of the antenna are obtained after calculation according to the data obtained by scanning.In this thesis,the plane and spherical near-field measurement methods are emphatically expounded,The near-field to far-field transformation and the diagnostic method of aperture field of the near-field amplitude and phase measurements and near-field scalar measurements are studied.The first half of this thesis introduces the basic theory and method of near-field amplitude and phase measurement,and the second half studies the basic theory of near-field scalar measurement and the fast near-field scalar measurement method based on aperture field shape.The core of the near-field amplitude and phase measurement is the stationary phase method and the plane wave spectrum expansion theory.Firstly,the mode expansion method is used to deduce the plane wave expansion formula,and the plane near-far field transformation formula without probe compensation is obtained.According to the Lorentz reciprocity theorem,the coupling equation between the probe and the antenna system is derived,and then the plane near-far field transformation formula and the aperture field diagnosis method considering the probe compensation problem are obtained.Next,the spherical wave expansion formula is deduced,and the difference between the mode coefficients without probe compensation and with probe compensation is analyzed.Because the spherical wave expansion formula is applicable to both the near field and the far field,so that the modulus coefficients of the near and far fields of the same antenna remain unchanged,and the spherical near and far field transformation formula is derived by using this point.The farfield pattern of the antenna can obtain the plane spectrum,and then the aperture field of the antenna can be diagnosed.The antenna near-field amplitude and phase measurement technology requires accurate amplitude and phase information to derive far-field data,etc.In the actual test,the measurement of the phase is directly and negatively affected by many reasons such as the probe position error,the accuracy of the transmission device and the relative stability of the connecting machine.In view of the problems encountered at present,a scalar field measurement technique that can obtain the far-field pattern of the antenna only by amplitude acquisition is required.The core of this technology is the phase restoration algorithm,which uses the collected amplitude information to restore the phase of the sampling point through an algorithm.On this basis,the complex field composed of the amplitude and the calculated phase is measured at the sampling point,and then the antenna far field calculation and aperture field diagnosis are carried out.In this thesis,the simulation data of the half-wave oscillator array is used to verify the theories of plane near-field amplitude and phase measurement,spherical near-field amplitude and phase measurement,plane near-field scalar measurement and spherical nearfield scalar measurement,and add the probe position error in the simulation to simulate the real sampling.Finally,the measured data of the waveguide slot array is used to verify these measurement methods,which proves the feasibility of these methods in the actual antenna measurement.