Preliminary experimental results are presented on novel nonreciprocal coupling between two identical dielectric image lines. This is produced by loading the coupling region with a longitudinally magnetised ferrite. Measurements in the frequency range 26.5–40 GHz show a differential insertion loss of greater than 15 dB, over a bandwidth of approximately 1.5 GHz between 30 GHz and 35 GHz, produced by reversing the bias field. The minimum insertion loss was approximately 5 dB over this bandwidth, and the return loss was better than 13 dB. These results can be improved and this effect can be used to develop four-port circulators for millimetric wavelengths.