GB652168A - Improvements in modulating systems for ultra short waves - Google Patents

Abstract

652,168. Wave-guides. SADIR-CARPENTIER. Jan. 29, 1948, Nos. 2710 and 2711. Convention dates, Feb. 5, 1947 and March 21, 1947. [Class 40 (viii)] [Also in Group XL (c)] A magnetron valve operating as a modulating element interposed in a wave-guide modifies simultaneously in opposite senses the co-efficients of wave transmission and reflection, the magnetron being interposed between two sections of guide, each of which is designed to convert plane-polarized into circularly-polarized waves, or vice versa. The transmitted waves are passed to a radiating horn as, say, vertically-polarized waves, and the reflected waves are diverted away from the wave generator and are either dissipated or are fed as horizontally-polarized waves into the same radiating horn. In Fig. 1, waves from a generator are fed into a rectangular guide 1, with their electric vector horizontal. They emerge into a square guide 6 the walls of which are at 45 degrees to the horizontal. Two waves having their polarizations at right angles are propagated through the guide 6, and owing to the phase-shifting effect of the rods 3, they enter the modulating zone 7 as circularlypolarized waves, as described in Specification 1333/48, (as open to inspection under Sect. 91). The modulating means provides a variable obstruction in the zone 7 with the result that the proportion of the wave energy transmitted and reflected varies in opposite senses in the rhythm of the modulation. The transmitted energy passes through a guide section 6<SP>11</SP> similar to the section 6 and appears in the output guide 5 and horn 12 as a plane polarized wave with horizontal electric vector. The energy reflected at the modulating zone 7 passes back through the guide section 6 and appears at the face 6<SP>1</SP> as a plane-polarized wave with vertical electric vector, which wave is unable to pass along the guide 1 but is fed into a guide 10. It may be absorbed in this guide by a dummy load, but preferably, passes through a phase-shifter 13 to the neck of the horn 12. The resultant radiated wave is thus vertically-polarized at one extreme of modulation and horizontally-polarized at the other. With intermediate degrees of modulation the wave is elliptically-polarized, the eccentricity of the ellipse varying with the degree of modulation. Fig. 7 shows the modulating magnetron 23 with an axial cathode 24 and a ring anode 28, an axial magnetic field being provided by coils 29. Modulating-voltage M is applied between cathode and anode to vary the diameter of the zone occupied by the electrons, none of which reach the anode. The rods 26, 261 which operate as in Fig. 1 to convert the polarization of the waves in the guides 21, 21<SP>1</SP> may also be used to convey heating-current for the cathode from the supply CH, and modulating-voltage M and H.T. supply current for the anode-cathode circuit. The aperture in the ring anode 28 may be of roughly cruciform shape as shown in Fig. 4.