Complete S-matrix in a microwave cavity at room temperature

submitted to PREWe experimentally study the widths of resonances in a two-dimensional microwave cavity at room temperature. By developing a model for thecoupling antennas, we are able to discriminate their contribution from those of ohmic losses to the broadening of resonances. Concerning ohmic losses, we experimentally put to evidence two mechanisms: damping along propagation and absorption at the contour, the latter being responsible for variationsof widths from mode to mode due to its dependence on the spatial distribution of the field at the contour. A theory, based on an S-matrix formalism, is given for these variations. It is successfully validated through measurements of several hundreds of resonances in a rectangular cavity