We compare the statistical properties of eigenvalue sequences for a gamma =
1 Bunimovich stadium billiard. The eigenvalues have been obtained in two w
ays: one set results from a measurement of the eigenfrequencies of a superc
onducting microwave resonator (real system), and the other set is calculate
d numerically (ideal System). We show influence of mechanical imperfections
of the real system in the analysis of the spectral fluctuations and in the
length spectra compared to the exact data of the ideal system. We also dis
cuss the influence of a family of marginally stable orbits, the bouncing ba
ll orbits, in two microwave stadium billiards with different geometrical di
mensions. [S1063-651X(99)12309-2].