GB861214A - Waveguide feed assembly for circular or linear polarization - Google Patents

Abstract

861,214. Waveguides. BENDIX CORPORATION. Oct. 6, 1959 [Oct. 16, 1958], No. 33873/59. Class 40 (8). A coupling between a rectangular waveguide and a horn comprises means whereby the polarization of the radiated energy may be changed at will from linear to circular and vice versa. The mode converter comprises three discs 14, 15, 16 having aligned central apertures which together form a circular waveguide. In each aperture is arranged a diametral rod 17. The discs have a thickness of one quarterwavelength and are assembled between a front plate 2 and a back plate 3, also one quarterwavelength thick. The back plate 3 comprises a waveguide section 4 designed to transform between the H 01 mode existing in a rectangular waveguide (not shown) and the H 11 mode in the discs 14, 15, 16. The front plate 2 comprises a section 5 of square waveguide corresponding to the square throat of horn 6. All the discs are rotatable and are mechanically coupled to each other by pin-and-slot mechanisms having a certain amount of lost motion. Two extreme angular positions of rest of the disc assembly are determined by stops 32, 33 in the back plate 3 which engage one or other of two shoulders 35 (one only shown) on the disc 16. In one angular position, the rods 17 are all in the same plane at right angles to the electric vector of the H 11 wave so that the linear polarization of the wave remains unchanged. In the other position, the rods lie respectively at angles of 45, 30 and 15 degrees to their original positions and effect a 45 degree rotation of the transmitted wave. A dielectric plate 8 in the throat of horn 6 is arranged to produce a 70-degree phase-shift between the equal orthogonal components of the obliquely polarized wave. The asymmetrical flare of the horn 6 produces a further 20 degrees of differential phase-shift, the total phase-shift amounting to 90 degrees whereby the polarization is transformed from linear to circular. The actuating mechanism comprises a toothed wheel engaging the toothed periphery of the disc 14. A handle 25 connected to the shaft of the toothed wheel is retained by springs in either of its extreme positions. Elliptically polarized radiation may be obtained by changing the angular setting of the discs 14, 15, 16 and adjusting the position of the dielectric plate 8. For this purpose, the plate is connected by rods 9 through slots in the side of the horn to a yoke 10 which carries an adjusting screw 11. A septum 13 equalizes the radiation pattern for the two components of the wave.