Abstract :
A simple method is described for measuring the fraction of power in spurious modes generated by a transducer in the presence of the main mode. This method is applicable when the energy in the spurious mode is small and its guide wavelength is different from that of the main mode. Briefly it involves measuring the input standing-wave ratio as a function of the position of a short-circuiting piston in the multi-mode waveguide. From the pattern of the absorption resonances so obtained, together with their shape and spacing, the modes can be identified and their energy contents calculated. The attenuation coefficients can be derived from the measurements if desired, but this is not essential for the calculation of the coupling coefficient.
