The microwave resonance characteristics of the fabricated device were measured by use of a pair of microwave probe antennas and a network analyzer. Fig. 2 shows the measured microwave transfer characteristics through the fabricated device. The resonance peaks in the Fabry-Perot cavity were observed clearly. The measured separation of the adjoining resonance frequency was ~1GHz at frequency around 15GHz. These results were in good agreement with the theoretical estimations. Therefore, single-mode microwave propagation characteristics in the designed frequency range were confirmed experimentally. In the Fig. 2, the transmission signal is rather small below 14GHz due to the cut-off characteristics of the horn antenna used in the measurement.