Determination of mode content and relative phase in highly overmoded circular waveguides by open-ended radiation pattern measurement

A number of techniques of mode content determination of highly overmoded circular waveguides based upon open-end radiation pattern measurements have appeared in the literature. Each of these techniques is found to possess various limitations in the decomposition of certain mode combinations. Some of the limitations can be eliminated by the inner-product method. This method provides for the determination of both the amplitude and the phase of the waveguide modes present at the output of the device under test. The inner-product method requires measurement of the phase pattern of the far-field radiation, information not easily obtained at higher microwave and millimeter-wave frequencies. The method is shown to be most useful when combined with the simpler mode content determination technique of R.J. Vernon et al. (1987). The application of the inner product method to the determination of the mode content of a TE/sub 01/-TE/sub 11/ mode converter is described.<>