Determination of TWT periodic delay line dispersion by means of coupled waveguide analysis

Phase dispersion of an alternate-slot coupled-cavity circuit suitable for use in TWTs (traveling-wave tubes) is determined by means of coupled mode theory. A circuit is modeled using the familiar waveguide elements: coaxial, cylindrical, and sector types. Their orthonormal modes are well known and form the basis vectors for constructing the possible delay line modes, both propagating and nonpropagating. Application of Floquet´s theorem as a boundary condition results in a direct determination of the phase shift per period of the structure at arbitrary frequencies. Provision in the analysis for multiply connected waveguides enables beam-hole effects to be included. Dispersion properties at midband are computed to be within 0.5% of measured values.<>