Electromagnetic Near-field Interpolation for Spherical Near-field to Far-field Transformations

This paper presents an electromagnetic (EM) near-field interpolation for spherical near-field (NF) to farfield (FF) transformations. The two-dimensional (2D) NF interpolation techniques are studied in this work including the 2D linear technique namely the bilinear and low-degree polynomials technique, called bicubic Spline, in order to reduce an effect of NF under-sampling data to FF antenna radiation pattern error. The NF-FF transformation algorithm is implemented by using the spherical wave expansion with trapezoidal rule numerical integration. In the investigation, an under-sampling NF data of the seven-patch array antenna is simulated from the CST Microwave Studio simulation program, where the sampling angles are larger than the maximum sampling angles criteria of the NF spherical sampling theorem. It is found that the FF radiation patterns of AUT from the proposed technique using Spline interpolation and simulated FF radiation pattern are in good agreement. The FF antenna radiation pattern error is reduced. The undersampling NF angles of 25.65 % are studied with FF radiation pattern magnitude error lower than 3 dB. The under-sampling NF data provides less time-consuming of NF data collection. The FF antenna radiation pattern error will be reduced by using appropriate NF interpolation techniques.