Design of a $\hbox {TM}_{01}{-}\hbox {TE}_{01}$ Transmission Line for High-Power Microwave Applications

In this paper, we report the design methods and numerical results for a kind of high-power microwave (HPM) circular-waveguide transmission line, which has a 90deg bend to change the wave propagating direction for certain purposes and, meanwhile, also acts as a TM₀₁-TE₀₁ converter, transforming the HPM sources generating TM₀₁ mode into the TE₀₁ mode. Two types of mode-conversion sequences, i.e., TM₀₁-TM₁₁-TE₀₁ and TM₀₁-TE₁₁-TM₁₁-TE₀₁ , are proposed. In both sequences, a 90^deg-bend TM₁₁-TE₀₁ mode converter with sinusoidal curvature is adopted. Besides, in the first sequence, a new configuration of serpentine TM₀₁-TM₁₁ converter is proposed, which provides high conversion efficiency with short length; in the second one, compact linear TM₀₁-TE₁₁ and TE₁₁-TM₁₁ converters are designed. These two types of transmission lines have similar transmission efficiencies of 98.2% and 98.6% (ohmic attenuation in Cu waveguides is included), respectively, at 3.5 GHz, with bandwidths (for mode-conversion efficiency >90%) of 6.0% and 5.7%, respectively.