Mixing of wavefunctions in rectangular microwave billiards

A set-up is described allowing the automatic registration of wavefunctions of quasi-two-dimensional microwave billiards of arbitrary shape. Tests of t he apparatus with rectangular shaped billiards showed that a precision of s ome percent in the wavefunction amplitudes can be obtained, as far as isola ted resonances are considered. For the case of overlapping resonances, howe ver, the measurement yields wavefunctions which are close to a symmetric an d an antisymmetric linear combination of the original rectangle eigenfuncti ons. The cause for this at first sight surprising result is discussed.