Design and Test of Broadband Rectangular Waveguide TE₁₀ to Circular Waveguide TE₂₁ and TE₀₁ Mode Converters

Abstract

In this paper, converters of TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\Box }_{{10}}$ </tex-math></inline-formula> –TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ }_{{21}}$ </tex-math></inline-formula> mode and TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\Box }_{{10}}$ </tex-math></inline-formula> –TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ }_{{01}}$ </tex-math></inline-formula> mode with similar exciting topologic structures are designed and verified for a cold test of gyro-TWT. Both the proposed converters are composed of three sections, including TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\Box }_{{10}}$ </tex-math></inline-formula> to TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\Box }_{{20}}$ </tex-math></inline-formula> mode converter with ridged twist waveguide, TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\Box }_{{20}}$ </tex-math></inline-formula> to TE <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">22</sub> mode converter with variable cross-shaped waveguide, and the last section TE <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">22</sub> to TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ }_{{21}}$ </tex-math></inline-formula> or TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ }_{{01}}$ </tex-math></inline-formula> mode converter ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\Box }$ </tex-math></inline-formula> represents the rectangular waveguide, <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> represents the cross-shaped waveguide, and ° represents the circular waveguide). The mode converters can be designed step-by-step and exhibit excellent wideband performance and high conversion efficiency. Simulation results reveal that the proposed TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ }_{{21}}$ </tex-math></inline-formula> mode and TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ }_{{01}}$ </tex-math></inline-formula> mode converters have less than 0.04 and 0.03 dB loss over 13.5- and 12-GHz bandwidths, respectively, while the return loss is below −25 dB. Prototype TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ }_{{21}}$ </tex-math></inline-formula> and TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ }_{{01}}$ </tex-math></inline-formula> mode converters were fabricated and back-to-back millimeter-wave measurements were performed to verify the design.