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Transmission Characteristics of Hybrid Modes in Corrugated Waveguides Above the Bragg Frequency

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Abstract

We studied the transmission characteristics of hybrid modes in a corrugated circular waveguide above the Bragg frequency to develop a broad-band transmission line for millimeter waves. Millimeter waves at 294 GHz were transmitted into a straight waveguide. From observed power profiles in waveguide cross-sections, a high attenuation rate of 0.13 dB/m was obtained. To match a theoretical attenuation constant with the experimental one, we introduced an ad hoc coefficient of conventional surface reactance in the waveguide wall. This was necessary because the wall began to look like the surface with a decreasing anisotropic reactance owing to the frequency above the Bragg frequency. Using nonlinear optimization for mode content analysis, the observed power profiles in the waveguide cross-section were matched with theoretical profiles. There was good agreement between the calculated and observed centers of power profiles and attenuation rate along the waveguide. The theoretical analysis showed that the magnetic field at the waveguide wall increases and the substantial attenuation takes place. Above the Bragg frequency coupling to backwards propagating modes is a point of consideration. A combination of the backwards propagating EH1,26 and the forward propagating HE11 modes satisfied the Bragg condition at 294.7 GHz which was the nearest frequency of operating frequency. A strong attenuation of the incoming HE11 mode by Bragg resonance was not expected due to large difference of 0.7 GHz. It becomes clear that the observed high transmission loss outside of the Bragg resonance can be explained by a decrease in anisotropic surface reactance at the wall.

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Acknowledgements

This work was supported by JSPS KAKENHI Grant No. 25247094 and was performed with the support and under the auspices of National Institute for Fusion Science, Collaboration Research program (NIFS13KOAR014) and Research Center for Development of Far-Infrared Region, University of Fukui, Collaboration Program (H28FIRDM005C and H28FIRDM014B).

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Authors and Affiliations

  1. Research Center for Development of Far-Infrared Region, University of Fukui, Fukui, 910-8507, Japan

    Kunizo Ohkubo, Teruo Saito, Yuusuke Yamaguchi, Yoshinori Tatematsu & Jun Kasa

  2. National Institute for Fusion Science, Toki, 509-5292, Japan

    Shin Kubo, Takashi Shimozuma & Kenji Tanaka

  3. Graduate School of Frontier Sciences, The University of Tokyo, Kashiwanoha, 277-8561, Japan

    Masaki Nishiura

Authors
  1. Kunizo Ohkubo
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  2. Teruo Saito
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  3. Yuusuke Yamaguchi
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  4. Yoshinori Tatematsu
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  5. Jun Kasa
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  6. Shin Kubo
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  7. Takashi Shimozuma
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  8. Kenji Tanaka
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  9. Masaki Nishiura
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Correspondence to Kunizo Ohkubo.

Appendix A: High Attenuation of the Hybrid Mode below the Bragg Frequency

Appendix A: High Attenuation of the Hybrid Mode below the Bragg Frequency

In the frequency domain satisfying d < λ/2, Z f = 1 is used. We plot X HE11 and α HE11 which are calculated by using the parameters of the waveguide as a function of f in Fig. 15. Near f = 35 GHz, α HE11 increases considerably. At this frequency, the TM component of the OHE11 mode is large because d HE11 = −0.41 for f = 35 GHz. In Fig. 15, the profiles of E y and H 𝜃 are shown. In the waveguide perimeter, a crescent shape in the H 𝜃 pattern appears, which leads to large transmission loss.

Fig. 15
figure 15

Results obtained from 35 GHz below the Bragg frequency with Z f = 1 for the OHE11 mode. The eigenvalue, attenuation, and E y and H 𝜃 are shown. The patterns of E y and H 𝜃 have crescent-shaped regions

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Ohkubo, K., Saito, T., Yamaguchi, Y. et al. Transmission Characteristics of Hybrid Modes in Corrugated Waveguides Above the Bragg Frequency. J Infrared Milli Terahz Waves 38, 853–873 (2017). https://doi.org/10.1007/s10762-017-0385-y

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  • DOI: https://doi.org/10.1007/s10762-017-0385-y

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