Study Of Sphere Near-Far Field Transformation Based On The Scattering Matrix Of Spherical Wave

Near-field antenna measurements obtain the properties and parameters of theantenna under test in high accuracy and efficiency. According to different measurementsurfaces, there are three types of near-field antenna measurement, the planar、cylindricaland spherical near-field measurements. The paper studied the spherical near-far fieldtransformation based on the scattering matrix theory of spherical wave, and verified thetransformation by simulation.First, the spherical wave expression of the antenna in any area was derived by thespherical wave expansion theory. Then, the relationship between the TransmissionCoefficients and the Wave Coefficients were derived through the method of sphericalwave scattering matrix when the system of antenna and probe was viewed as awaveguide junction with two ports. The Transmission Formula between the antenna andprobe also could be obtained through the coordinate system rotation. After this, theResponse Coefficients of linear polarization probe which was the first-order probe indifferent areas were studied and solved.Then, the analytical solution and the discrete solution of Transmission Coefficientswould solved by the sampled signals at the probe. At this point, the near-far fieldtransform would be carried out by using the Transmission Formula and the ResponseConstant of the probe.At last, the theoretical near fields and far fields of a dipole and array antenna weresolved respectively. Then, the near field data were used as the sampling single in thenear-far field transformation. The transformed results of both antennas agree well withthe theoretical far fields respectively.