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 TM
₀₁
-TE
₀₁
converter, transforming the HPM sources generating TM
₀₁
mode into the TE
₀₁
mode. Two types of mode-conversion sequences, i.e., TM
₀₁
-TM
₁₁
-TE
₀₁
and TM
₀₁
-TE
₁₁
-TM
₁₁
-TE
₀₁
, are proposed. In both sequences, a 90
^deg
-bend TM
₁₁
-TE
₀₁
mode converter with sinusoidal curvature is adopted. Besides, in the first sequence, a new configuration of serpentine TM
₀₁
-TM
₁₁
converter is proposed, which provides high conversion efficiency with short length; in the second one, compact linear TM
₀₁
-TE
₁₁
and TE
₁₁
-TM
₁₁
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.