Mode coupling phenomenon in high permittivity NRD guide with asymmetrically remained small air gap

It is known that a high permittivity NRD (nonradiative dielectric) guide, where an LSM01 mode mainly propagates, suffers from irregular transmission phenomena. Since high permittivity materials such as ceramics and alumina have rough and hard surfaces, we assumed that this problem was caused by an asymmetric remaining small air gap between the metal plates and the high permittivity dielectric materials in the NRD guide. From the theoretical and experimental investigations, it is clear that the LSM01 mode is liable to couple with an unwanted mode, while an LSE01 mode, being another nonradiating mode, is hard to couple with such a mode.