S band Improved Metamaterial Slow-Wave Structure Yanshuai Wang, Zhaoyun Duan*, Yan Nie, Sen Yang, Qing Zhou, Zhanliang Wang, and Yubin Gong National Key Laboratory of Science and Technology on Vacuum Electrons, School of Physical Electronics University of Electronic Science and Technology of China Chengdu, China *E-mail:
[email protected] Abstract—In this paper, we present an S band improved metamaterial slow-wave structure (SWS), which is in order to increase the bandwidth of the previously proposed metamaterial SWS. A drift tube is added in the metamaterial unit cell, and the improved SWS has been further studied and analyzed by using Ansoft HFSS and CST Particle studio particle-in-cell solver. The simulated results show that the bandwidth of the improved metamaterial SWS has been effectively increased compared with that of the metamaterial SWS, and the peak output power of the S band backward-wave oscillator based on the improved SWS is 20.7 MW with an electronic efficiency of 92.4%. Keywords—Metamaterial; slow-wave structure; bandwidth; backward-wave oscillator; peak output power.
I. INTRODUCTION The metamaterials have some unique electromagnetic properties, such as the reversed Cherenkov radiation (RCR) [1], which enable applications such as the metamaterial vacuum electron devices [2]-[8]. In our previous studies, we have proposed an all-metal metamaterial with the negative effective permittivity, and a new sort of backward-wave oscillators (BWOs) based on the metamaterial slow-wave structure (SWS) also has been presented and studied [9]-[12]. The simulated results show that the novel metamaterial BWO has the distinguished properties such as miniaturization and high electronic efficiency compared with the conventional BWOs, but the bandwidth is relatively narrow. In this paper, we propose an improved metamaterial SWS which can effectively increase the bandwidth.
Jinjun Feng National Key Laboratory of Science and Technology on Vacuum Electronics Beijing Vacuum Electronics Research Institute Beijing, China
Fig.1. The improved metamaterial SWS.
Fig. 2 illustrates the bandwidth of the fundamental mode of the improved metamaterial SWS and metamaterial SWS, and the phase velocity curves of the zeroth spatial harmonic of the fundamental mode extracted from Fig. 2 for the SWSs are shown in Fig. 3. From Figs. 2 and 3, it can be concluded that the bandwidth of the improved SWS in which the phase velocity of the electromagnetic wave vp is less than the speed of light in vacuum is 30 MHz larger than that of the metamaterial SWS, which means the tunable bandwidth of the BWOs also can been increased.
II. SIMULATION We propose an improved SWS as shown in Fig. 1. Compared to the previous metamaterial SWS, the drift tubes are added in the complementary electric split ring resonators (CeSRRs) [12]. Here, it should be noted that other parameters of the CeSRR unit cell and the SWS are completely consistent with those in the earlier work [12]. The SWS is the key component of the BWOs which can greatly affect the beamwave interaction efficiency and the output power of the BWOs. The high-frequency characteristics of the improved SWS have been studied, which are also compared with those of the previous metamaterial SWS, as shown from Fig. 2 to Fig. 4.
Fig. 2. Comparison between dispersion curves for the two SWSs.
This work was supported in part by the National Natural Science Foundation of China (Grant Nos. 61471091, 61611130067, and 61531010). Fig. 3. Comparison between phase velocity curves for the two SWSs.
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Fig. 4 shows that the interaction impedance defined on the central axis of the beam tunnel of the improved SWS is even a little higher than that of the metamaterial SWS, which means that the BWOs based on the improved SWS could have high electronic efficiency and the output power.
even higher interaction impedance, and the particle-in-cell results predict that it is valuable for the compact high-power vacuum electron device. REFERENCES [1]
Fig. 4. Comparison between interaction impedance curves for the two SWSs.
Fig. 5 shows that the peak output power of a signal generated at 2.024 GHz is 20.7 MW with an electronic efficiency of 92.4%ˈwhile the beam voltage and the current are 280 kV and 80 A, respectively.
Fig. 5. Peak output power of the generated signal for the S band BWO based on the improved metamaterial SWS.
III. CONCLUSION In this paper, we propose an S band improved metamaterial SWS which is based on the metamaterial SWS that has been studied before. The simulation results of the high-frequency characteristics demonstrate that the improved SWS has relatively broader bandwidth than the metamaterial SWS, but
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