GB767531A - Improvements in or relating to polarised radio mirrors - Google Patents

Abstract

767,531. Radio reflectors. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. May 18, 1955 [June 9, 1954], No. 16998/54. Class 40(7) The invention is concerned with radio mirrors of the kind comprising a plurality of wires, strips, slats or baffles. Such mirrors can be used in transmit-and-receive aerial systems to reflect waves' of one polarization and pass waves of another. It has been found that, where mirrors having a plurality of parallel wires or the like are used in conjunction with lenses, trouble arises due to the phase aberration and other errors which occur. These are in part due to energy passing through the lens at a considerable distance from its axis having its polarization components at an angle to the corresponding components of the axially directed energy. Consequently they are differently affected by the parallel wire mirror. According to the invention a wire or like mirror 5 intended for use in conjunction with a lens 6 is constructed with the wires diverging from a point Z external to the effective part of the mirror and defined by the intersection of the plane containing the mirror, the plane (EFGH) through the focus of the lens and parallel to the lens, and the plane (BCKJ) passing through the focus and a representative linear polarization vector (at the lens) of the polarization which the mirror is intended to-reflect. The aerial system shown is for a radar system with a transmitting horn 1 radiating a vertically polarized wave. The energy is reflected by mirror 5 through lens 6 and circular polarizer 7 and radiated as a circularly polarized wave. Reflected signals returned are converted into a horizontally polarized wave which passes through the mirror 5 to receiving horn 3. By the use of a mirror 5 constructed in accordance with the invention phase aberration and the like are largely avoided. The invention is not limited to the reflection of waves of vertical polarization and Fig. 3 (not shown) depicts schematically a mirror for reflecting waves of a given arbitrary direction of polarization.