Coupled back-strapped bar-line analysis for low-noise CFA´s

A comprehensive modal analysis of the strapped bar line has been performed using an adaptation of a method ascribed to Fletcher. A determinantal system of equations is generated upon application of boundary conditions which include provisions for multiple straps, side and back walls, and vanes on cooling channels. The formulation also provides direct means for the evaluation of the circuit coupling and characteristic impedances. Comparisons between measured dispersion and impedance values and those based upon the new formulation show excellent agreement for typical CFA circuits. Extension of the model to the coupled delay-line system employed in a low-noise CFA reveals that the main mode splits into anti-symmetric and symmetric modes. Their relative mix on the circuit depends upon the amplitudes and phases of the split-feed driving signals. Proper input control of the independent modes is seen to be implicated in a significant low-noise mode of CFA operation.