Highly Efficient Gyrotron Mode Converter With a Launcher Changing Angular Spectrum of the Operating Mode

To minimize diffraction losses and the dimensions of the quasi-optical converter, a unique waveguide launcher is proposed to be used in the output system of a 28-GHz gyrotron operating on the TE $_{-{1.2}}$ mode with a small Brillouin angle at its input. The launcher converts the gyrotron operating mode into a Gaussian-like wave beam with an efficiency of more than 98%, propagating with a big Brillouin angle to the axis of the launcher. The launcher is designed using a hybrid synthesis/method of moment (MoM) + multilevel fast multipole algorithm (MLFMA) approach, and two versions of the waveguide launcher are manufactured using two different technologies. The experiment confirmed the high efficiency of the quasi-optical converter.