GB832531A - Travelling wave oscillation generator - Google Patents

Abstract

832,531. Backward-wave tubes. STANDARD TELEPHONES & CABLES Ltd. Dec. 14, 1956 [Dec. 20, 1955], No. 38286/56. Class 39(1). In a travelling wave tube the beam passes through a first delay line section 15, Fig. 4, terminated non-reflectively at both ends to generate backward wave oscillations therein, the backward wave oscillations velocity modulating and bunching the beam and the bunched beam giving up energy to a second separate delay line section 17 supporting a forward wave from the far end of which the output is taken, the forward-wave section being arranged to have a falling output power/frequency characteristic compensating for the rising characteristic of the backward wave section, so that an overall flat response is obtained. Due to the absence of an output circuit the characteristic of the backward wave section is smooth. The delay lines are preferably both helices, as shown, but may be replaced by other delay structures such as interdigitated lines. The beam is preferably annular (generated by a ring cathode 11) and can pass outside both helices, Fig. 3 (not shown) or inside the first helix 15 but outside the second helix 17, as shown, to an annular collector 12, the beam being focused in the central portion of its travel by a solenoid 18. The cathode and beam need not be ring shaped ; e.g. the beam can be ribbon shaped or generally of hollow form. The reflectionless terminations 13, 14, 16 are graphite coatings on the helix support rods. The output helix is preferably given a non-circular, e.g. elliptical cross section so as to avoid cancellation of space harmonies varying angularly around the helices. The output is taken to a coaxial line by a tapered pitch and diameter helix section and a flared continuation of the outer conductor 19 of the coaxial line.