GB789927A - Improvements relating to slow wave structures - Google Patents

Abstract

789,927. Travelling wave tubes. GENERAL ELECTRIC CO. Feb. 28, 1956, No. 6184/56. Class 39(1). [Also in Group XL(b)] An arrangement for electromagnetically coupling two coaxial helical slow wave structures spaced apart along their common axis and wound in the same sense comprises a coupling helix coaxial with the structures and wound in the opposite sense and extending between and overlapping each of the two structures for such an axial length as to cause the effective transfer of the electromagnetic energy in one structure to the other structure. As shown, a travelling wave tube comprising an electron gun 10, collector 19 and solenoid 21, is provided with two helices 23, 28 separated by a gap 26, the first helix 23 being maintained at the same potential as that of the accelerating anode of the gun 10 and the second helix 28 at a slightly higher potential. The two helices are electromagnetically coupled by a helix 32 wound with the same pitch angle but in the opposite sense to that of helices 23, 28 and overlaps each of the adjacent ends of the two helices by one quarter of a beat wave length. Undesired frequencies are attenuated by a high loss coating 34 and the unwanted backward wave at the operating frequency by rods 34<SP>1</SP> of lossy material. A drift tube may be provided between the two helices 23, 28. Coupling helices may also be used to feed energy to, and to extract energy from, the travelling wave tube. Instead of a physical gap between the two helices 23, 28, a single helix may be provided with a centre section coated with lossy material so as to form an effective gap for radio frequency currents.