Computational methods for modeling of complex sources

Abstract

Purpose -The purpose of this study is to develop and compare two methods of determining the total field, including phase information, when only field amplitudes have been measured on a set of planes in the near field of a complex electromagnetic source. Design/methodology/approach -The first method is a gradient-based optimization algorithm, based on the adjoint fields. The second method employs an optimization algorithm based on the phase angle gradients of a functional. Findings -The first method, the adjoint field method, is functioning well for a 2D test case. The second method, the phase angle gradient method, gives very good results for 3D test cases.Research limitations/implications -The next step is to test the methods with results from real measurement data. Practical implications -The developed methods are intended for use in dosimetry studies and other applications, where the field distribution from electromagnetic sources are needed. Originality/value -The methods extend previously made constant phase approximations. The present methods are useful in situations where the electromagnetic source is hard to model.

Performance Evaluation of Phase-Angle Gradient Method for Phase Retrieval Based on Low-Frequency Amplitude-Only Near-Field Data

“…One can divide plane 1 into a square grid with the grid cell area ∆S. If the point in the middle of the square number p is represented byr p , the Cartesian components of the electric fieldĒ in any point r on the other measurement planes can be calculated [9] with the expressions…”

“…However, if the operation frequency is significantly reduced to MHz or even nearly to DC, phase retrieval in the region of a few wavelengths separation can be much harder to achieve. In view of this, Johansson et al [9] have recently proposed another phase retrieval method known as the Phase Angle Gradient Method (PAGM). Preliminary results have demonstrated that the method is able to perform phase retrieval at 100 MHz [10].…”

Comparison Between Two Phase-Retrieval Methods for Electromagnetic Source Modeling

“…One can divide plane 1 into a square grid with the grid cell area ∆S. If the point in the middle of the square number p is represented byr p , the Cartesian components of the electric fieldĒ in pointr can be calculated [3] with the expressions…”

“…There are several applications where such modeling is useful. Some examples are near-field to far-field transformations [1], antenna diagnostics [2] and electromagnetic dosimetry [3]. Phase-retrieval methods are interesting, since measurements of both amplitude and phase generally are more complicated and require more expensive equipment than phaseless measurements.…”

“…In [3], we have introduced two phase retrieval methods, the adjoint field method and the phase angle gradient method (PAGM). Results for both methods were given.…”