Conformal-mapping design tools for coaxial couplers with complex cross section

Abstract

Numerical conformal mapping is exploited as a simple, accurate, and efficient tool for the analysis and design of coaxial waveguides and couplers of complex cross section. An implementation based on the Schwarz-Christoffel Toolbox, a public-domain MATLAB package, is applied to slotted coaxial cables and to symmetrical coaxial couplers, with circular or polygonal inner conductors and external shields. The effect of metallic diaphragms of arbitrary thickness, partially separating the inner conductors, is also easily taken into account. The proposed technique is validated against the results of the finite-element method, showing excellent agreement at a fraction of the computational cost, and is also extended to the case of nonsymmetrical couplers, providing the designer with important additional degrees of freedom.

Broad-band coaxial directional couplers for high-power applications

“…Thus, the first step of the design procedure is the evaluation of characteristic impedances or per-unit-length capacitances (for nonsymmetrical structures) as functions of the transversal geometrical parameters. This task is performed with great accuracy and at a fraction of the computational cost of other numerical techniques such as the finite-element method by the NCM code developed by Teppati et al [19], which allows the study of couplers having cross sections both circular and rectangular, symmetrical and nonsymmetrical, and with and without diaphragms. In the most general nonsymmetrical case, the usual description in terms of even-and odd-mode impedances and does not hold, and one must define a capacitance matrix (1) where , , and are the per-unit-length capacitances shown in Fig.…”

“…1 shows the cross section of a transversally nonsymmetrical rectangular coaxial coupler with a diaphragm. The transversal analysis is carried out with a fast and accurate algorithm based on numerical conformal mapping (NCM) [19], providing the coupling factor and the characteristic impedances as functions of the structure dimensions. A technique derived from stripline theory [14] is then applied to the longitudinal design of the nonuniform diaphragm.…”

Ka-band surface-mount directional coupler fabricated using micro-rectangular coaxial transmission lines

“…Several methods have been used to compute the even-and odd-mode impedances in the past. A numerical implementation of conformal mapping has been used to design directional couplers with multiple conductors, giving accurate results [10]; however, symmetry is necessary in one plane. Because some line cross sections that have been fabricated--though are not presented here--do not fit these constraints, the characteristic impedances for different cross sections is calculated using a more general method.…”

Fabrication and nonlinear characterization of GaN HEMTs on SiC and sapphire for high-power applications

“…For high-power and high-reflectivity GaN devices, the active load-pull setup has been further improved with new ad hoc features: high-power bias tees, lowloss directional couplers [18], and fast current shutter so as to protect probe damaging in case of device failure.…”