Optimized dual frequency quasi-optical mode converter for high power gyrotron

A compact dual-frequency quasi-optical mode converter (QOMC) for high-performance gyrotrons, operating in the mode at 104.9 GHz and the mode at 140 GHz, has been developed. This converter utilizes a dimpled wall launcher and incorporates perturbations based on coupled mode theory, supported by a specialized mirror system. To analyze the electromagnetic field in the launcher wall for both frequencies, a MATLAB code was developed. The radiation field emitted by the launcher is evaluated in free space, while the mirror system consists of a quasi-elliptical mirror, an elliptical mirror, and a parabolic mirror, ensuring precise phase correction. Optimizing key parameters such as radius, perturbation amplitude, and length successfully achieved efficient mode conversion and beam shaping within a compact 130 mm design. Comprehensive simulations using FEKO confirmed that this shortened launcher maintains high mode purity and low loss. Remarkably, its length is significantly shorter than other existing models and typical theoretical estimates, demonstrating the effectiveness of parameter optimization in developing compact, high-performance launchers. The results indicate that the total length of the launcher is only 130 mm, with a cut length of 20 mm, comprising 15.38% of the total launcher length. Simulation results show that after phase correction, the Gaussian mode content reaches 99.14% and 97.23% at 104.9 GHz, and 98.64% and 96.44% at 140 GHz for scalar and vector Gaussian modes, respectively. These findings highlight the proposed dual-frequency mode converter’s excellence in generating Gaussian beams while maintaining a compact and efficient design. This work presents a practical approach to optimizing QOMCs for dual-frequency gyrotrons, expanding their potential applications in high-power millimeter-wave systems.