title: Simple Expressions for the Design of Linear Tapers in Overmoded Corrugated Waveguides.
abstract: Simple analytical formulae are presented for the design of linear tapers with very low mode conversion loss in overmoded corrugated waveguides. For tapers from waveguide radiusa2toa1, witha1<a2, the optimal length of the taper is 3.198a1a2/λ. Here, λ is the wavelength of radiation. The fractional loss of the HE11mode in an optimized taper is [Formula: see text]. These formulae are accurate whena2≲ 2a1. Slightly more complex formulae, accurate fora2≤ 4a1, are also presented in this paper. The loss in an overmoded corrugated linear taper is less than 1 % whena2≤ 2.12a1and less than 0.1 % whena2≤ 1.53a1. The present analytic results have been benchmarked against a rigorous mode matching code and have been found to be very accurate. The results for linear tapers are compared with the analogous expressions for parabolic tapers. Parabolic tapers may provide lower loss, but linear tapers with moderate values ofa2/a1may be attractive because of their simplicity of fabrication.
authors.affiliation: Plasma Science & Fusion Center, Massachusetts Institute of Technology, 167 Albany St., Bldg. NW16, Cambridge, MA 02139, USA.
authors.forename: S C
authors.initials: SC
authors.lastname: Schaub
authors.affiliation: Plasma Science & Fusion Center, Massachusetts Institute of Technology, 167 Albany St., Bldg. NW16, Cambridge, MA 02139, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Shapiro
authors.affiliation: Plasma Science & Fusion Center, Massachusetts Institute of Technology, 167 Albany St., Bldg. NW16, Cambridge, MA 02139, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Temkin
keywords: Corrugated waveguide; Gyrotron; THz; Taper; mm wave