Design of a Dual-Mode Input Structure for K/Ka-Band Gyrotron TWT

Abstract

A dual-band gyrotron traveling wave amplifier (Gyro-TWT) can reduce the size, cost, and weight of a transmitter in dual-band radar and communication systems. In this paper, a dual-mode input coupler for K/Ka dual-band gyrotron traveling wave amplifier (Gyro-TWT) is designed. This structure is composed of two different types of input couplers, one is the coaxial input coupler for the Ka-band TE2,1 Gyro-TWT and the other is a Y-type input coupler for the K-band TE1,1 Gyro-TWT. For reducing the backward wave of the TE2,1 mode reflecting into the Y-type input coupler to influence the operating bandwidth, a Bragg reflector with a strong mode selective characteristic is inserted between these two couplers, which can make the reflection coefficient of the TE2,1 mode better than −1 dB and the phase matched in the whole bandwidth, and the transmission coefficient of the TE1,1 mode can reach better than −1 dB. Based on the simulation results, the −1 dB bandwidth of the Ka-band TE1,0⬜-TE2,1◯ mode input coupler reaches 3.32 GHz and the −1 dB bandwidth of K-band TE1,0⬜-TE1,1◯ mode input coupler reaches 3.15 GHz. The designed dual-mode input coupler has the advantages of broad bandwidth and low loss and can be well used in dual-band Gyro-TWTs.