GB672770A - High frequency electron discharge device and circuit - Google Patents

Abstract

672,770. Travelling-wave tubes. RADIO CORPORATION OF AMERICA. Dec. 8, 1947 [Jan. 25, 1947], No. 32340/47. Class 39 (i). A travelling wave amplifier has separate input and output helixes 5, 6, Fig. 1, terminated non-reflectively at either end, and the beam after being modulated by the helix 5 is accelerated by a D.C. field before passing into the second helix 6 so as to increase the output energy. The helix 6 is preferably of variable pitch, as shown, to correspond with the progressive reduction in beam velocity, and the helix 5 may or may not be of variable pitch. The input and output are injected and removed via coaxial lines 20, 37, the inner conductors of which are helices of varying pitch to match the impedance of the helices 5, 6. The free ends of the helices 5, 6 are terminated by non-reflective resistors R, R<SP>1</SP>. The envelope of the device comprises two non-magnetic metal cylinders 10, 18 with dielectric 19 between, 18 being more positive than 10, and a partition 11 with an aperture 15 for the beam shields the helices 5, 6 from one another and prevents feed-back. A coil 26 focuses the beam. In a modification, Fig. 2 (not shown), the envelope 10 is grounded instead of being at a negative potential relative to ground as in Fig. 1. In a further modification, Fig. 3 (not shown), the output helix 6 is constructed of overlapping portions with semi-conducting material such as titanium dioxide interposed so as to provide resistances for D.C. but negligible impedance for the travelling wave; a positive D.C. bias is applied to helix 6 so that an axial potential gradient is set up along the helix. The coaxial line connected to the output helix is joined to a quarter-wave sleeve located in a metallic enclosure. The sleeve forms one pole of the output and the inner conductor is capacitatively coupled to the enclosure to form the other pole of the output and directly connected to the positive battery terminal. The tube corresponding to 18 may be connected to a top on the battery or to ground; in the latter case the dielectric sleeve corresponding to 19 may be dispensed with.