Near-field to far-field transformation of cylindrical scanning antenna measurement using two dimension fast-fourier transform

Abstract

Radiation characteristics of an antenna should be tested through a precise measurement procedure. To provide an actual parameter of an antenna radiation, measurement must be performed in the far-field region and its distance is proportional to the antenna's dimension. Therefore, in a limited space of an anechoic chamber facility, antenna measurement has a constraint to a maximum dimension of the antenna under test. Near-field measurement method has been an alternative to overcome this problem. However, additional techniques, such as sampling, scanning mechanism, transformation computation, cannot be avoided to obtain the actual antenna radiation parameters. In this research, we study cylindrical scanning technique to obtain sampling data because it is simpler than the spherical scanning in mechanical setup and can produce radiation pattern results in completely two dimension polar diagrams. Our purpose is to provide low cost and reasonable performance of a near-field measurement system. Two dimension Fast-Fourier Transform is used to process and analyze the near-field data into the far-field data. Other methods, i.e. one dimensional Fast-Fourier transform and numerical method, are also performed to compare the accuracy and efficiency of the proposed method. Near-field data generated from experiment data measured of 8-array micro-strip antenna at resonant frequency 3.35 GHz. Transformation results show that average deviations of one dimension Fast-Fourier Transform, two dimension Fast-Fourier Transform and the numerical method are 6.83 dB, 3.04 dB, and 3.77 dB, respectively. These results show the minimum discrepancies between the transform and the expected far-field obtained by using the two dimensions Fast-Fourier Transform. This method has shown near-field measurement and transformation can predict the far-field radiation characteristics.