Mode Couplers and Multimode Measurement Techniques

The measurement of harmonic and spurious signals in waveguide systems is complicated by the fact that one must usually deal with a multimodal measurement. Since the energy may propagate in any mode consistent with the frequency and waveguide geometry, the measurement system used must discriminate between these different modes. A simple and direct approach to this problem is through the use of "mode couplers" which couple selectively to any desired mode. Theoretical and practical details for mode couplers for the first five modes in rectangular waveguide are presented, as well as the application and limitations of this measurement technique.