GB776797A - Improvements in or relating to modulating devices for micro waves - Google Patents

Abstract

776,797. Radio reflectors; amplitude modulation; responders. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Oct. 6, 1955 [Jan. 3, 1955], No. 47/55. Classes 40(5) and 40(7) A radio wave reflector which provides an amplitude modulated reflected signal and is suitable for use as a radar responder consists of a device having successive reflecting' surfaces differing in level by a whole odd number of quarter-wavelengths of the energy concerned and means for causing relative motion between said device and incident energy. The surfaces are preferably arranged round a rotatable wheel 3 which as shown has alternate flat projecting surfaces 5 and flat recesses 6. If incident energy is known to come from one direction only, a focusing lens 1 is provided bringing the incident beam to a focus at a position corresponding approximately with the edge of the wheel. For an omnidirectional arrangement a number of lenses can be arranged in a ring round the wheel 3 or lenses may be omitted altogether. In the latter case, however, the depth of modulation will be reduced. In order to obtain a better concentration of reflected energy in a given plane the rotatable wheel may be located between fixed conductive truncated cones so as to be, in effect, at the throat of an annular horn (Fig. 3, not shown). A reflector according to the present invention can also be mounted co-axially inside a structure such as is described in Specification 776,258. Such a structure has reflector elements distributed round it, each element being substantially at right angles to the diametrically opposite element, so that waves of a given polarization passing through one wall are reflected by the other. The structure may be constructed to bring such waves to an approximate focus at the surfaces of a rotatable wheel as described above, modulated waves being returned along the incident path from whichever direction they are received (Fig. 4, not shown).