Millimeter-wave TE₀₁–TE₁₁–HE₁₁ mode converter using overmoded circular waveguide

Abstract

The paper presents overmoded circular waveguide mode converters (TE₀₁ into HE₁₁ with TE₁₁ as an intermediate mode) used in a 42 ± 0.2 GHz, 200 kW gyrotron transmission line system for plasma heating in electron cyclotron resonance heating application. To convert mode from TE₀₁ to TE₁₁, we have used wriggle converter method with a deformation in the converter axis and for TE₁₁ to HE₁₁ mode converter the depth of corrugation decreases gradually from to . Both the converters are optimized in terms of design parameters using mode field matching technique. The TE₀₁ to TE₁₁ mode converter showed a conversion efficiency of 95% (predicted 99%) for a length of 1205 mm, while TE₁₁ to HE₁₁ mode converter gave conversion efficiency of 99% (predicted 99.98%) for a diameter of 32 mm. Cross-polarization isolation of 31.7 dB is obtained in TE₁₁ to HE₁₁ mode converter. Convergence of the theoretical values and the simulated results indicates that the converters meet the system requirements.

Keywords:

• Overmoded circular waveguide
• mode converters
• coupled wave theory
• periodic perturbation
• mode conversion efficiency
• radiation pattern
• ECRH (electron cyclotron resonance heating)

Acknowledgments

Authors would like to thank Board of Research in Nuclear Sciences (Department of Atomic Energy-Govt. of India) for giving financial support under the grant no. 39/14/11/2016-BRNS/34196 and Institute of Plasma Research, Gandhinagar-India for providing technical Support and Testing facilities. They are also thankful to CHARUSAT (Charotar University of Science and Technology) University to give permission to carry out this research work.

Additional information

Funding

This work was supported by Board of Research in Nuclear Sciences (Department of Atomic Energy – Govt. of India) [grant number 39/14/11/2016-BRNS/34196].