Multipole and S-Parameter Antenna and Propagation Model

Antenna models relating voltage excitations to radiated fields are an important part of any electromagnetic measurement, with applications ranging from two-way communication systems to full-wave inverse scattering. Here, we derive a two-antenna model relating the multipole expansion of the fields radiated and received by antennas to S-parameter measurements between them. We also show how to determine the antenna model parameters from numerical simulation and how to include single-path scattering of near-by objects from their T-matrices. Finally, we validate the model experimentally using two rectangular waveguide apertures. This model is based on the source-scattering matrix used in near-field single-antenna measurements, where we have developed it for direct S-parameter measurements.