Computer aided measurement of multimode fields in waveguides

A method for computer aided measurement to analyze closed and open multimode structures, e.g., waveguides, travelling wave structures, is presented. Measurements are realized with a sonde having a very low coupling coefficient with relation to waveguides positioned manually, and connected through an attenuator to a differential analyzer connected at the other hand to the signal generator. The phase and amplitude values are digitized, and fed to a computer. The obtained values are then further analyzed in a larger computer. Precision of measurements attained is plus minus two grad and plus or minus 0.2 dB. The mathematical solution of the nonlinear equations system is an application of the Prony algorithm to waves in a medium with axial translational symmetry. The method was tested by measuring multimodal fields in a circular waveguide with smooth walls. Based on fairly accurate field data, the results of the analysis are checked, the accuracy of the wave number values is established, and the optimum parameters of the analysis are obtained.