A system and method for measuring a thickness of a refractory wall of a gasifier using electromagnetic energy is disclosed. The system includes a waveguide with a bistatic or monostatic phased array antenna at one end. The waveguide is operably connected to a Network Analyzer that generates a pulse of electromagnetic energy with a desired bandwidth. The pulse is transmitted through a coaxial cable to the waveguide. The reflection of the pulse is received by the waveguide and input to a data acquisition system. An output device displays the resolvable discontinuities in impedance encountered by the pulse in its propagation path in the system