An equipment status monitoring system (10) and method of operating includes first (40) and second (50) microwave mirrors in a plasma processing chamber (20) each forming a multi-modal resonator. A power source (60) is coupled to the first mirror (40) and configured to produce an excitation signal. A detector (70) is coupled to at least one of the first mirror (40) and the second mirror (50) and configured to measure an excitation signal. At least one of the power source (60) and the detector (70) is coupled to a divergent aperture (44).