Experimental mode content analysis technique for complex overmoded waveguide systems

In this paper, short time Fourier transform techniques are used to analyze the mode content of overmoded waveguides. The analysis is applied to transmission through straight sections, bends, and T-junctions. In addition to determining the modes with the dominant contributions to the response, the presence of mode conversion in bends and T-junctions is observed. The direct application of this technique is channel characterization of an HVAC duct system, which behaves as a multimode waveguide network at RF frequencies when used for indoor wireless communications.