This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. IEEE TRANSACTIONS ON ELECTRON DEVICES 1 A Novel Wire-Wrap Slow-Wave Structure for Terahertz Backward Wave Oscillator Applications Changpeng Xu, Yong Yin, Liangjie Bi, Zhang Zhang, Zhiwei Chang, Abdur Rauf, Safi Ullah, Bin Wang, and Lin Meng Abstract—An innovative wire-wrap structure was applied as the slow-wave circuit for a backward wave oscillator (BWO) operating in terahertz (THz) band. The construction of the device features a periodic fine copper wire, a rectangular ridged waveguide, and a rectangular cavity in the upper cover plate. Based on the novel structure, the performance of the device presented by dispersion characteristic, coupling impedance, and S-parameters was analyzed and optimized in the design process. The electron beam parameters with an outer diameter of 0.26 mm have relatively low accelerating voltage around 1.2 kV and beam current of 0.05 A (the current density is 94 A/cm 2 ). Under such conditions, numerical simulation results predict that the novel oscillator is capable of achieving the output peak power in excess of 154 mW and a tunable 3-dB bandwidth over 24 GHz in the range from 324 to 348 GHz. In addition, the machining and assembling methods of wire-wrap structure are another original invention for the physical processing of THz BWO. Index Terms— Backward wave oscillator (BWO), terahertz (THz) radiation, vacuum electron device, wire- wrap slow-wave structure (SWS). I. I NTRODUCTION T HE research of terahertz (THz) technology has become a momentous frontier in the domain of electronic infor- mation science, as the development and applications of low frequency electromagnetic wave spectrum are gradually sat- urated. Numerous materials have their absorbing peaks in THz band with frequency range from 0.3 to 10 THz, and high frequency sources are very attractive for a wide range of research and technical applications [1]. The study of THz wave on its substantial characters has produced plenty of significant applications on security inspection, environmen- tal monitoring, astronomy, information and communications, nondestructive testing, materials science, and the imaging of cellular level [2]–[6]. As a precondition of the exploitation of THz frequency band, how to efficiently generate a stable THz signal is a critical factor that has limited evolution of THz Manuscript received August 29, 2016; revised October 23, 2016; accepted November 8, 2016. This work was supported in part by the National Natural Science Foundation of China under Grant 61671116 and in part by the Fundamental Research Funds for the Central Universities under Grant ZYGX2015J037 and Grant ZYGX2015J039. The review of this paper was arranged by Editor M. Thumm. (Corresponding author: Yong Yin.) The authors are with Vacuum Electronic National Laboratory, School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China (e-mail: yinyong@uestc.edu.cn). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TED.2016.2628045 device. At present, the backward wave oscillator (BWO), a typical vacuum electron device, is considered as the most promising device to produce THz radiation wave. The slow-wave structure (SWS) is the kernel in the BWO, whose main function is to exchange the energy between electron beam and the electromagnetic field. It is also acknowl- edged to be a major element in the performance and various parameters of the whole tube decisions. In the past decades, several representative SWSs, such as corrugated waveguide, sinusoidal waveguide, and the folded waveguide, were intro- duced for the realization of BWO [7]–[9]. The other new kinds of emerging SWSs, such as quasi-parallel-plate structure, the enlarged cavity volume groove structure with a metallic ring inclusions, clinotron structure, and the double corrugated waveguide, were innovated and modified on the basis of preceding classical ones [10]–[14]. All of the available structures are based on conventional microfabrication technology, such as deep reactive ion etch- ing, microelectrodischarge machining technology, deep X- ray Lithographie Galanoformung and Abformung process and micro/nano-Computer numerical control-(CNC) machining. For SWS, the primary challenge is to achieve a surface rough- ness of SWS below the skin depth (66 nm at 1 THz) for min- imizing the ohmic losses [15]. In order to meet these require- ments, a novel wire-wrap method was employed to process and assemble SWS, and this machining method can provide SWS with smooth surface and the fabrication convenience. In this paper, we present a wire-wrap SWS for BWO operated in the THz band, as shown in Fig. 1. The slow- wave circuit was realized by wrapping the copper wire around the upper cover plate and modern microfabrication techniques, which assures an effective interaction with a cylindrical beam. It consists of a periodic fine copper wire, a rectangular ridged waveguide, and a rectangular cavity in the upper cover plate. The manufacturing and assembling technique are included in this paper, and the physical realization of this oscillator was accomplished. Based on the above conditions, the advantages of the proposed BWO consist in novel wire-wrap structure, low cost, easy assembly for high yield, high interaction impedance, extremely low operating voltage of 1.2 kV, and low current density of 94 A/cm 2 . Finally, the simulation results by particle in cell (PIC) demonstrate that the BWO with the wire-wrap SWS is a simple and promising way for the generation of THz wave. 0018-9383 © 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.