一种新型同轴TEM-圆波导TE11模式变换器

 提出了一种新型同轴插板式模式变换器，可以实现同轴TEM到圆波导TE₁₁模式的变换。介绍了这种模式变换器的工作原理：即通过在同轴波导中沿轴向插入金属板，将同轴TEM模变换成扇形截面波导TE₁₁模，进而利用不同扇形截面波导中的相移改变电场分布的轴对称性，在同轴波导中形成同轴TE₁₁模，最后将同轴TE₁₁模转换为圆波导TE₁₁模式。基于这一原理设计了一个中心频率为3.8GHz的同轴TEM-圆波导TE₁₁模式变换器，并进行了数值模拟。模拟结果表明：这种模式变换器可以承受高功率，中心频率上转换效率为98.5%，转换效率大于90%的带宽超过10%，在3.5~4.1GHz的频率范围内反射损耗低于0.3dB。

A new type of coaxial TEM-circular waveguide TE11 mode converter

Many high-power microwave (HPM) sources utilize an azimuthally symmetric output mode, like the TM_(01) circular waveguide or the coaxial TEM modes. If radiated directly these modes produce a doughnut-shaped pattern, with a bore-sight null. A novel mode-conversion technique for transforming the azimuthally symmetric mode to one with a more desirable radiated pattern is described and analyzed. The novel approach is as follows: first, the coaxial TEM mode is converted to TE_(11) fan-shaped waveguide mode by inserting fins into the coaxial waveguide, then the coaxial TE_(11) mode is got by varying the length of the fins, finally the coaxial TE_(11) mode is transformed to TE_(11) circular waveguide mode. A mode converter for 3.8GHz based on this principle is designed and optimized. The calculated results show that it has high conversion efficiency about 98.5% at 3.8GHz with an over 10% bandwidth where the efficiency exceeds 90%. The return loss is below 0.3dB in the range of 3.5～4.1GHz. The converter has the input and output co-aligned on the same axis and it’s easy to fabricate.