Anderson localization in a string of microwave cavities

The field distributions and eigenfrequencies of a microwave resonator which is composed of 20 identical cells have been measured. With external screws the periodicity of the cavity can be perturbed arbitrarily. If the perturb ation is increased a transition from extended to localized field distributi ons is observed. For very large perturbations the field distributions show signatures of Anderson localization, while for smaller perturbations the fi eld distribution is extended or weakly localized. The localization length o f a strongly localized field distribution can be varied by adjusting the pe netration depth of the screws. Shifts in the frequency spectrum of the reso nator provide further evidence for Anderson localization. [S1063-651X(99)10 310-6].