Spatial and frequency selection of waves in pseudoperiodic slow-wave structures

The principles of the joint selection of spatial harmonics and the extension of passbands of pseudo-periodic slow-wave structures (SWSs) are considered. Relationships for calculating the continuous spectrum of spatial harmonics are presented. Recurrence formulas for determining the input reflection coefficient from an SWS section are derived and used for the analysis of frequency characteristics. Selection of spatial harmonics and transformation of passbands in pseudoperiodic folded SWSs ( a folded waveguide, an interdigital structure, etc.) are investigated. The possibility of extraction of either the first or the fundamental spatial harmonic in a frequency band from 30% to one octave and simultaneous suppression of spurious harmonics, including backward waves, is demonstrated. Owing to this feature, pseudoperiodic SWSs can be used in high-power wideband traveling-wave tubes.