GB586689A - Improvements in antennas - Google Patents

Abstract

586,689. Wave guides ; aerials. WESTERN ELECTRIC CO., Inc. Aug. 16, 1944, No. 15672. Convention date, Aug. 21, 1943. [Class 40 (v)] An antenna, for effecting conical scanning in a microwave radar device, comprises an open ended wave guide rotatable about an axis disposed at an acute angle to the longitudinal axis of the guide. As shown in Fig. 1, waves polarized as shown by arrow 26, are supplied by the transmitter-receiver 1 to a main wave guide 2, pass through an orifice 9, a circular polystyrene window 11 in the guide 2, and through a circular polystyrene window 13 into a short circular rotatable guide section 12 to the antenna aperture 14 thereof, the radiated wave being reflected by a metallic parabolic reflector 4. A piston 8, in the upper dummy section of the main guide 2 tunes the cavity 27 and matches the guide impedance to that of the window-opening 11 therein. The window-openings 11, 13 are coupled through a zero impedance produced by dimensioning the flange 18 to form with the corresponding wall area of guide 2 an open ended quarter wave line. The guide section 12 is secured to and has its longitudinal axis disposed at an acute angle to a " Plexiglass " (Registered Trade Mark), or other dielectric shaft 19, rotated by a motor 20. The shaft 19 lies along the principal axis of the reflector 4, the focal plane 5 of which is coplanar with the slightly elliptical antenna aperture 14, and the focus 6 is preferably spaced from the central point 16 of aperture 14 a distance equal to or less than the antenna aperture radius. The tuning piston 8 may be replaced, Fig. 2 (not shown), by an inclined deflector and the window opening 11, connected to a stub guide section having a circular flanged opening similar to and facing flange 18 so that the two flanges form an openended quarter wavelength line. In the arrangement shown in Fig. 5, both the main guide 15 and dummy guide 50 have portions extending perpendicular to the axis 7 of the reflector 4. The main guide is connected to the transmitterreceiver 1 by a coaxial line 52, having the inner conductor 53 extending transversely into the guide 51 so that H11 waves having a polarization 26 are transferred between guide 51 and line 52. A tuning piston 55 produces unilateral propagation in the guide 51, both for transmitted and received waves. The shaft 19 of motor 20 has a " Mycalex " (Registered Trade Mark) section 57 and a " Plexiglass " section 58 and bears in polystyrene plates 62, 63 fixed by dielectric rods 59 to a plate 60. The central circular portion 64 of plate 63 faces the opening 10 in the guide 51 and also faces the polystyrene window 13 in the rotatable guide section 12, the antenna aperture 14 of which is also preferably closed by a polystyrene window. Zero impedance couplings 17 are included between the guide opening 10 and the plate section 64, and between the latter and window 13 in guide section 12. The entire antenna system is rotatable in two directions at right angles, indicated by arrows 66, 67 so that the direction of a target can be determined in known manner by aligning it with the axis 7.