Phase Retrieval Methods for Electromagnetic Source Modeling

Doktorsavhandling, 2011

Modeling of the field distributions from electromagnetic sources is of interest for various applications including electromagnetic compatibility investigations, near-field to far-field transformations, antenna diagnostics and electromagnetic dosimetry. In order to determine whether exposure safety guidelines, such as the EU directive 2004/40/EC, are complied with, source modeling methods are important. Two methods for determining the total field, including phase information, when only field amplitudes have been measured on a set of planes in front of an electromagnetic source have been developed. The first method, the adjoint field method, is a gradient based optimization algorithm based on the adjoint fields. The second method, the phase angle gradient method, employs an optimization algorithm based on the phase angle gradients of a functional. The two methods have been tested for numerical test cases with both high and low frequencies and the phase angle gradient method was found to perform best. Moreover, it gave results that are in excellent agreement with the correct phase. The phase angle gradient method was also tested for measured magnetic flux density with low frequency from a transformer and for electric field with high frequency from a mobile phone. For the cases with measured field the obtained phase angles on the measurement plane closest to the source gave calculated field on other measurement planes that agrees well with measured field.