Patent GB-579859-A (GB)
Title: Improvements in radio wave reflection apparatus for the observation of objects, such as aircraft
IPC: G01S1/02
Filed: 1944-02-09
Abstract: 579,859. Radiolocation. WESTERN ELECTRIC CO., Inc. Feb. 9, 1944, No. 2439. Convention date, Nov. 24, 1942. [Class 40 (v)] [Also in Group XXXVI] In a radiolocation system the plane of polarisation of the transmitted wave is rotated continuously so that a relative strong reflection is obtained each time the plane of polarisation reaches an optimum angle with respect to a target. Amplitude modulation of the wave reflected from a target may be detected and its phase compared with that of a locally generated wave of the same frequency to indicate changes in the aspect of the target, or when the aspect of the target is unchanging, its distance from the point of observation. The antenna system comprising a dipole 24 and reflector 26 is mounted on a bearing block 86 and yoke 82 permitting scanning in two dimensions. The dipole and reflector are mounted on a shaft 22 in bearings 23, the axis of which coincides with the axis of the transmitted beam, and are rotated about this axis by a motor 36 and gearing 34 at a rate of 100 to 200 r.p.m. which is sufficient to enable the maximum reflections to provide indications on an oscilloscope which appear to be substantially constant. The dipole is connected through slip rings 18, brushes 20 and leads 60 to the transmitter 14 and receiver 44 through a duplexing unit 16, which isolates the receiver from the transmitter pulses and may comprise a protective device such as a gas-filled tube. A recurrence frequency oscillator 10 controls a pulse generator 11 which may be of the type described in Specification 477,875, [Group XXXV], producing narrow pulses at a frequency of from 2 to 4 k.c/s. which are fed through amplifier 12 to modulate the transmitter 14. Oscillator 10 also controls a pulse generator 52 the output from which is fed to a ranging unit 50 providing an adjustably delayed pulse which is fed to the vertical deflecting plates of the cathode ray oscilloscope 46 to which are also fed the signals from the receiver 44, so that the range of a target may be determined by aligning the ranging pulse and target echo signal. A sweep generator 48 controlled by the pulse generator 52 provides a time base sweep which is applied to the horizontal deflecting plates of the oscilloscope. The frequency of amplitude modulation of signals reflected from a target is twice the spin frequency of the antenna and the output at this frequency from receiver 44 is fed to a phase indicator 42 to which is also fed the reference alternating output of the same frequency from alternator 38, driven by motor 36. The phase indicator provides an indication of the angular relation of the target with respect to the observation point, while if the target is such that the optimum polarisation plane for reflection is fixed, the output from the phase indicator may be used as an indication of the distance of the target, or if the equipment is carried in an aircraft, it may be used to indicate the altitude of the aircraft. In modifications, the rotation of the plane of polarisation may be obtained by feeding a stationary paraboloidal bowl reflector from a rotating dipole, or a circular waveguide horn may be energized by a wave the polarisation of which is rotating, or two dipoles positioned in quadrature about a common centre point may be energized by equal components of the transmitter energy in phase quadrature.