A coax ring‐sidearm power extraction design

We report on a successful klystron power extraction design, in which a TEM coaxial mode is transmitted into the TE10 mode of a WR90 rectangular waveguide at 11.42 GHz, with very little TEM reflection and almost vanishing asymmetric (TEM→TE11, or monopole to dipole) reflectance. Our coupler consists of a ring (disk) around the coaxial waveguide, and a coax‐WR90 sidearm junction (see Fig. 1). The methods used in the design are numerical simulation, performed on the MAFIA3 T3 time‐domain module and on HFSS (High Frequency Structure Simulator), and analytical treatment to guide the numerical runs. The demerit parameters (dipole reflectance and TEM reflection) can be reduced as much as desired (to zero in principle), the only limitation being computer run time and memory. The results reported are accurate to a few percent.