Radiation method for the measurement of mode-conversion levels

A novel method for the determination of mode-conversion levels in overmoded waveguides is described. It relies on a swept-frequency measurement of the perturbation of the dominant-mode radiation pattern of the open-ended waveguide, owing to the presence of higher-order modes. Results are reported for mode-conversion effects in corrugated waveguides at frequencies near 9 GHz. Excellent agreement with the trapped-resonance method is demonstrated, although the present technique has advantages over this method when the mode excitation level is high or the waveguide length is imprecisely known.