GB792387A - Microwave transducer - Google Patents

Abstract

792,387. Waveguide accessories. HUGHES AIRCRAFT CO. Jan. 10, 1956 [Jan. 28, 1955], No. 876/56. Class 40 (8). [Also in Group XL (c)] Apparatus for controlling the ellipticity of polarized microwave energy comprises an axially symmetrical waveguide 10 within which are mounted a Faraday element 12 for producing a non-reciprocal rotation of planepolarized energy and a quarter-wave dielectric plate 16 for producing a 90 degree phase-shift between orthogonal components of the plane polarized wave. The element 12 consists of a cylindrical slug of ferromagnetic ceramic, e.g. ferrite, and is supported by dielectric members 13, 14 within the axial magnetic field of a solenoid 18. The element produces a Faradayeffect rotation of the plane of polarization of a plane-polarized H 01 wave propagated in the guide, the magnitude of the rotation being dependent upon the strength of the axial magnetic field and the absolute sense of the rotation being independent of the direction of propagation. For energy propagated from left to right the magnetic field can be used to vary the angle between the plane of polarization and the plane of the quarter-wave dielectric plate 16. The plate produces a 90-degree phase-shift between the components of the plane-polarized wave resolved in the plane of the plate and at right-angles thereto. The output wave is thus elliptically polarized, the ellipticity being dependent upon the relative amplitudes of the orthogonal components of the plane wave and hence, ultimately, upon the strength of the magnetic field. The apparatus may be used as a polarization analyser, energy to be analysed being fed from right to left. The apparatus may form part of the common transmit-receive channel of a pulsed radar set, the plate 16 being arranged parallel to the direction of polarization of the unrotated input pulse. By taking into account the reversal in the rotatory sense of polarization due to reflection and the fact that the signal traverses the quarter-wave plate twice, it may be deduced that the total angular difference between the planes of polarization of the transmitted and received pulses at the left-hand edge of the plate is (180-20) degrees, where # degree is the rotation of the Faraday element. In traversing this element the pulse is rotated through # degree in the same absolute sense both on transmission and reception. The result is that the echo pulse has at the input end of the guide 10 a plane of polarization displaced 180 degrees from that of the transmitted pulse, i.e. the planes of polarization are parallel. The Specification describes a construction in which the phase shifter is orientated to make an angle of 45 degrees with the plane of polarization of the incident wave. A magnetic field in the Faraday element producing a 90 degree rotation in the incident wave will result in circular polarization.