Study Of Sphere Near-to-Far Field Transformation Based On Sphere Wave Mode Expansion

Spherical near-field measurements have been one of the best ways in high-performance antenna testing. The measurement accuracy and efficiency are decided by near-field data sampling and mathematical transformation. In this paper, spherical Near-to-far field transformation is studied which based on spherical near-field measurements theory.Based on the classic sphere wave mode expansion theory, the expression of near-field spherical wave expansion were driven, and both with and without the probe-compensated the expressions for spherical near-to-far field transformation driven by near-field data was given, and the far-field expression derived also. Then the parameters of these expressions were solved accurately.Taking the practice near-far field antenna measurement system as an example, it analyzed the structure of system and the component of hardware and the function of developed system test soft. Taking a horn antenna as the AUT with the software HFSS, it calculate the near-field and far-field data of the AUT. And next the far-field data of the AUT would be derived with the near-field data into the spherical near-to-far field expression. At last, the far-field data by the expression was compared with the data by HFSS, and the better result shows the correctness and effectiveness of the algorithm. At last, a real horn antenna was measured by the system, and some good results were reached, it shows our algorithm has strong practicality.