Monitoring rotating machinery using radio frequency probes

Systems and methods for monitoring rotating machinery are disclosed. Transmitter and receiver antennas can be provided with access to the rotating machinery. At least one receiver signal resulting from at least one transmitter signal that has propagated through a portion of the rotating machinery can be obtained. A first signal pair can be formed from a first receiver signal and a first transmitter signal, or from first and second receiver signals obtained from spatially-separated receiver antennas, or from first and second receiver signals which are attributable to different transmitter signals. Amplitude and phase information of a plurality of frequency components for each signal in the first signal pair can be determined. A set of comparison values for the first signal pair can be determined by comparing respective frequency component phases or respective frequency component amplitudes. A characteristic of the rotating machinery can then be analyzed using the comparison values.