Coupled-Cavity Velocity-Modulated High-Frequency Electron Discharge Devices

1,198,707. Travelling-wave tubes. VARIAN ASSOCIATES. 5 Dec., 1967 [8 Dec., 1966], No. 55183/67. Heading H1D. A slow wave structure for a travelling-wave tube comprising a number of coupled cloverleaf type cavities is characterized in that the cavities are coupled to a lossy terminated waveguide to suppress unwanted modes. Fig. 3 shows a section of a cloverleaf cavity 29 including four finger sections 32 and coupled by T-shaped slots 42 to an adjacent cavity (not shown). Arcuate waveguide sections 50 and 51 are coupled by irises 52 to diametrically opposed leaf portions 40; the waveguides have a cut-off frequency between the upper edge of the operating band and the #-point of the fundamental operating mode and are tapered from maximum height at the coupling regions to zero height at the terminated ends, and the inner surfaces of the waveguide are coated with lossy material. The walls of the slots 42 may also be coated with lossy material to suppress slot modes. In a modification, Fig. 4 (not shown), the waveguides extend in opposite directions from a common input, and the coupling slots are of elongate form. In a further modification, Fig. 5 (not shown), waveguides similar to those in Fig. 3 are coupled to each leaf portion, the waveguides being half a wavelength long at the #-point frequency. In the travelling-wave tube illustrated (Fig. 1, not shown) the slow wave structure is provided with a coaxial line input and a waveguide output. As an alternative the tube may be of the hybrid type with a klystron input section.