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 TM01 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 TE11 fan-shaped waveguide mode by inserting fins into the coaxial waveguide, then the coaxial TE11 mode is got by varying the length of the fins, finally the coaxial TE11 mode is transformed to TE11 circular waveguide mode. A mode converter for 3.8GHz based on this principle is designed and optimized. The calculated results show