In this work the transmission properties of flat wicrowave cavities will be disscused. For the distribution of the transmission fluctiation exists theoretical predictions for the dependence on the number of channels and the time reversal symmetrie. This results are valid for microwave experiments, if the used cavitie is flat enough. Then the quantum mechanical Schrödinger-equation and the electrodynamical Helmholtz-equation are equivalent. The time reversal symmetrie can be broken in microwave experiments by introducing ferrites. In the first section the phase-breaking properties of ferrites will be discussed theoretically. In the case of semi-infinite, finite, and metal-backed ferrite slabs expansions of the Fresnel-formulas are found. Furthermore the scatttering properties of metalic and dielectric cylinders are discussed, to show the differences to the scattering on ferrite hollow cylinders. In the second section the transmission properties of asymmetric and symmetric microwace billiards will be examined in dependence of the channel number. The experimental results will be compared with theoretical and numerical results, which include the absorption as a new aspect. The signatures of the channel number and the time reversal symmetrie are preserved. Furthermore the energy derivation of the transmission (thermopower) is compared with numerical results.