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Derivation and analysis of near field tofar field transformation algorithm for spherical scanning

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2019
Korkmaz, Hülya
This thesis focuses on the improvement of a far field transformation algorithm of spherical near field scanning by using different quadrature techniques for numerical integration process. In this thesis, spherical vector wave expansion of E field is studied and numerical calculation for expansion coefficients of E field is performed. In the scope of this study quadrature techniques like Gauss, Trapezoid and Simpsons are investigated and advantages and disadvantages of these techniques are discussed. A decision criteria of quadrature technique for a particular function is also discussed and efficiency of these techniques is compared. Spherical far field transformation algorithm considered in this study is applied to electric and magnetic Hertzian dipoles (directed on z axis and located at (0,0,0)) and expansion coefficients are calculated with Gauss, Trapezoid and Simpsons quadrature. Also, expansion coefficients of Hertzian dipoles directed along the x axis and shifted along the z axis are calculated by using coordinate transformation and rotation. After the calculations of expansion coefficients, far field transformation is performed by using derived algorithm and far field radiations are plotted. This study is mainly devoted on the far field transformation of a spherically scanned near field data and transformation of this data is performed by applying near field to far field transformation algorithm with Trapezoid and Simpsons quadrature techniques and effectiveness of these two techniques is discussed. This study also includes the derivation of probe compensation algorithm to eliminate the probe effects from transformed data. In chapter 5, probe compensated coefficients are calculated by considering the coefficients of the probe and using the coordinate transformation and rotation. (See Appendix A and Appendix B). Far field pattern by using compensated coefficients is also analyzed to visualize the probe compensation effect.