Microwave simulation of quantum tunneling: Detection limits of superluminal processes

Delay-time measurements with a microwave setup, where an undersized waveguide simulates a quantum mechanical potential barrier, have been extended sufficiently below the cutoff in the attempt to obtain a direct evidence of superluminal behaviours. The obtained results are in agreement with the predictions of the phase-time model even below a crossing frequency where superluminal effects become appreciable. More evident results have been obtained by means of an open air transmission experiment with horn antennas and in a diffraction experiment. Eventually, an interpretation of these facts is given on the basis of a signal analysis along the lines of the Sommerfeld-Brillouin procedure, suitably modified taking into account frequency band limitations. (author)