Antenna Midfield Measurement Method

Antenna measurement is an important part of antenna development.Far-field measurement is still the most widely used as the most authoritative measurement method.However,due to the small size of many anechoic chamber,indoor far-field measurements are limited by finite distance.The cost of upgrading the measurement system and increasing the size is enormous.Therefore,this paper proposes two different midfield measurement theories to solve the problem of finite distance in the far-field antenna measurement.First,this article briefly reviews the meaning and status of antenna pattern measurements.Combining the shortcomings of the classical measurement methods in practical applications,I affirmed the concept of midfield antenna measurement.And according to the characteristics of the antenna radiation field in different spaces,I have divided the field area more carefully.Similar to the derivation of the far-field distance criterion,I proposed the criterion of distance in the middle of the field on the basis of previous research.Second,after a brief description of the necessary basic knowledge of electromagnetic fields.I derive a midfield antenna measurement method based on far-field approximation by deriving a formula for the antenna radiation field of the surface antenna.Due to insufficient distance,the midfield pattern has distance-related phase factors,the method mathematically transforms the phase factor in the midfield pattern expression to obtain a linear relationship between it and the far field pattern.The linear relationship shows that the far field pattern can be represented by a set of midfield patterns.We only need to do simple processing on the midfield measurement pattern data to get a more accurate far field pattern.Third,I introduced some necessary special functions.Through the derivation of the theory of antenna-cylinder wave expansion,I obtained another mid-field measurement method based on cylindrical wave theory.Compared with traditional cylindrical near-field measurements,This method approximates the far region of the cylindrical wave function and its application to one-dimensional stationary phase method in solving the integral process.The process of solving the cylindrical spectrum is simplified,and the near-field cylindrical measurement is extended to the far-field approximation.Therefore,the far-field pattern of antenna radiation can be calculated simply by requiring an approximate solution of the spectrum.A comprehensive analysis of the two measurement methods was performed to compare the advantages and disadvantages.Finally,I made a concluding remark in the full text.This part systematically summarizes the work done in the whole paper,affirms the research results of the two theories mentioned above,and takes into account the small deficiencies.I have made an outlook on the development direction of midfield measurement,and proposed two new midfield correction ideas based on the two measurement methods studied in this paper,and provided guiding suggestions for subsequent research.