GB644768A - Improvements in and relating to waveguide devices - Google Patents

Abstract

644,768. Wave-guides. MINISTER OF SUPPLY. Oct. 15, 1948, No. 26886. [Class 40 (viii)] [Also in Group XL (c)] A wave-guide capable of supporting an H 11 wave with either of two given perpendicular directions of polarization is coupled to waveguide feeds at orthogonally related spaced points in the walls of the guide so that a wave with either of the given polarizations may be launched in the guide by energizing the waveguide feeds with energy of appropriate phase and direction of polarization. As shown, a circular guide 7 is coupled to the in-line arms 3, 4 ; 5, 6 of an H-plane " T " 1 and an E- plane " T 2 at orthogonally-related spaced points. An H 10 wave in the T-arm of the H- plane " T " 1 produces in phase fields in guides 3, 4 indicated by full line arrows, which combine in the main guide 7 to launch an H 11 wave polarized in the direction shown. An H 10 wave in the T-arm of the E-plane " T '' 2 produces anti-phase fields in guides 5, 6 (as shown) by dotted arrows, which combined in the main guide 7 to give a wave polarized in a perpendicular direction. One pair of feed guides may be used, fed from the H- or E-plane arms of a " magic-T," Fig. 2 (not shown). The length of the feed guides from the circular guide to the mid-point of the T is preferably an odd number of half wavelengths. The arrangement may be used in a diplex or duplex system with a common frequency but different directions of polarization for each channel, or in a transmitter-receiver arrangement. A circularly polarized wave may be produced by replacing the circular guide by a nearly square guide, with the feed guides of each pair coupled to adjacent sides. In this case, a wave having two components with electric fields perpendicular to the walls of the guide, but differing velocities of propagation is produced by feeding one T-arm, and the length of the guide may be selected so that these components are 90 degrees out of phase at the output, giving a wave with circular polarization. A circularly polarized wave entering the guide produces, at the feed points, a resultant wave polarized at right angles to the resultant produced by feeding the first T-arm, so that an output may be taken from the second T-arm. This arrangement may be used in a receiver-transmitter or radar system, using circularly polarized waves.