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.
Highlights
Gyrotron traveling wave amplifiers (Gyro-TWTs) utilize the relativistic electron cyclotron maser instability to realize a high-power microwave source with high conversion efficiency [1]
A Q-band TE01 Gyro-TWT with an output power of 152 kW at 41 dB saturated gain was developed in the University of Electronics Science and Technology of China [9]
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
Summary
Gyrotron traveling wave amplifiers (Gyro-TWTs) utilize the relativistic electron cyclotron maser instability to realize a high-power microwave source with high conversion efficiency [1]. The National Tsing Hua University reported a Ka-band TE11 Gyro-TWT with off-axis electrons, which can produce 93 kW saturated peak output power at 70 dB stable gain and 26.5% efficiency with a 3 dB bandwidth of 8.6% [8]. The University of Strathclyde reported a large orbit Gyro-TWT in W-band, the corresponding peak power is 3.4 kW, the gain and bandwidth are 37 dB and 5.8 GHz [12], respectively. The University of Electronic Science and Technology of China designed a Ku/Ka-band dual-frequency Gyro-TWT input coupler, but its −1 dB bandwidth is only 2 GHz [19]. A dual-mode large bandwidth input coupler for K/Ka Gyro-TWT is theoretically designed.
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