Broadband HE04 mode exciter for W-band confocal Gyro-TWA

A new method to excite HE₀₄ mode in wide bandwidth for W-band confocal gyrotron travelling wave amplifiers (gyro-TWAs) is presented. The mode exciter consists of a TE₄₀ mode exciter and a TE₄₀-HE₀₄ mode waveguide transition section. Numerical results show that the mode exciter achieves an optimal transmission of -0.55 dB and a relative 3 dB transmission bandwidth of ~17%. The mode exciter shows broad bandwidth and flat transmission characteristics. Besides, it is compact and easy to be fabricated, which can be applied to cold test experiments of the interaction circuit.