Wave phenomena in a planar periodically corrugated waveguide are investigated experimentally at the microwave range of frequency. Measurements of the transmission properties show that the location of the gap in the frequency spectrum as well as its width depends on the relative position of two corrugated plates. The transmission varies from zero to a maximum value upon a shift of one periodic plate with respect to another on the half period of the corrugation. The results confirm the theoretical prediction of the geometry-driven spectrum transformation from a band-structure form to a gapless one upon such a shift of the plates. In physics of solids, this transformation corresponds to rnetal-insulator transition. (C) 2005 American Institute of Physics.