Effect of Eccentricity on Transmission in a Coaxial Bragg Structure
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Effect of Eccentricity on Transmission in a Coaxial Bragg Structure Shi-Chang Zhang & Xiao-Hui Chen & Ying-Xin Lai
Received: 7 August 2007 / Accepted: 30 August 2007 / Published online: 12 October 2007 # Springer Science + Business Media, LLC 2007
Abstract In practice a coaxial Bragg structure always has an eccentricity between the outer-wall and inner-rod axes. Numerical simulations are carried out to analyze the effect of the eccentricity on the transmission in a coaxial Bragg structure. Results demonstrate that the effect of the eccentricity is minimized and becomes negligible when the phase difference between the outer and inner corrugations is π, no matter if the eccentricity is parallel or oblique. Keywords Coaxial Bragg structure . Eccentricity . Corrugation phase difference . Transmission
1 Introduction Bragg structures have been widely employed in tunable lasers, photonic devices, integrated circuits, and high-power masers [1–3]. Particularly, a metallic Bragg structure is regarded as a suitable construction of overmoded cavities for high-power cyclotron auto-resonance maser (CARM) and free-electron laser oscillators in millimeter and sub-millimeter wave ranges [4–9]. Recently, much attention has been paid to coaxial Bragg structures due to their attractive peculiarities [10–16]. Generally speaking, in practice a coaxial structure always has eccentricity between the outer-wall and inner-rod axes, for example, a parallel or an oblique misalignment. As indicated in Refs. [17] and [18], the misalignment has substantial influence on the eigenvalues and electromagnetic fields distribution inside a coaxial waveguide and on the properties of a coaxial-cavity gyrotron. To the best of our knowledge, however, the effect of the eccentricity in a coaxial Bragg structure has not yet been studied. By making use of the
S.-C. Zhang (*) : X.-H. Chen : Y.-X. Lai Institute of Photoelectronics, Southwest Jiaotong University, Campus Mail Box 50, Chengdu Sichuan 610031, People’s Republic of China e-mail: [email protected]
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Int J Infrared Milli Waves (2007) 28:1043–1050
CST software [19], the present paper provides a numerical analysis for this subject. To ensure the creditability, in Section 2 we examine the numerical model in terms of the reported experiment [14]. Then in Sections 3 and 4 the influences of a parallel and an oblique eccentricity on transmission are demonstrated. Finally, conclusions are drawn in Section 5.
2 Creditability of numerical simulation model Figure 1 shows the longitudinal-section view of a coaxial Bragg structure, where a0, lout, ϕout are the outer-wall average radius, corrugation depth and phase, b0, lin, ϕin are the inner-rod average radius, corrugation depth and phase, Pb is the corrugation period, and L is the structure length, respectively. We choose the lines per wavelength to be 10, the mesh line ratio limit to be 10, giving a total number of mesh cells of 3346560 when we employ the CST software [19] to calculate electromagnetic fields in the coaxial Bragg structure. To exam
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