GB627690A - Improvements in or relating to means for detecting the presence of objects by means of electromagnetic waves - Google Patents

Abstract

627,690. Radiolocation; thermionic valve circuits; wave-guides. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. June 15, 1945, No. 15318. Convention date, Nov. 26, 1943. [Classes 40 (v), 40 (vi) and 40 (vii)] The aerial device for the production of the rotating directional beams for transmission and reception in a scanning radar system comprises synchronously revolving excitation elements which maintain the same relative angular positions and pass successively before the openings of series of fixed juxtaposed horns. Aerial system.-The electromagnetic horns are joined together to produce a single large horn divided into sectors, Figs. 9 and 10, the dimension a1 in the elevation of the electric vector of the individual horns being small so that a large number of elements constitute a sectionally-divided horn which covers an arc of 180 degrees as shown but which could cover 360 degrees for all normal scanning in azimuth. The individual horns are excited in groups by a rotary distributer comprising a rectangular wave-guide section closed at one end by a piston P and energized by an element t fed from a coaxial line f. The line f is coupled via a rotating joint to a further wave-guide, Figs. 12 and 13 (not shown), leading to the appropriate transmitter or receiver. The rotating coupling comprises an extension of the inner conductor of the line f terminating in a copper disc close to the lower wall of the guide while the outer conductor of the line forms a flange capacitively coupled to the upper wall of the guide. A dynamic counterweight is provided for the line f. The dimensions of the rotating distributer are such that several of the sectional horns are energized simultaneously and a radiation lobe such as would be produced by a single horn having the same aperture as that of the combined sections, rotates in space at the same speed as the distributer. A matching iris may be provided in the mouth of the waveguide distributer. Fig. 14 illustrates separate but identical transmitting and receiving aerials E and R mounted in a casing m provided with a radiation transmissive window P. A motor M drives, by worm gearing r, the distributers D, D1, which couple the aerials to the waveguides g, g1 associated with the transmitter and receiver. The motor M also drives via gearing r1 and in synchronism with the scanning beam, units C and C1 which are employed in the time-base generation. The complete radar system, Fig. 19. A recurrence frequency generator G of 2000 c/s. controls the pulse transmitter E and receiver R associated with the aerials 1 and 2. The unit C comprises two parallel fixed coils B, B<1> which are fed in series from the generator G and two quadrature spaced rotating secondary coils b, b<1>, the outputs of which, after amplification at L<1>, and L2, are fed via the push-pull transformers 5, 6 to the vertical and horizontal deflecting plates of the cathode-ray tube C to produce the resultant straight line trace M, M<1> on the screen thereof, the angular position of which corresponds with the orientation of the aerial radiation pattern. The output signals from the receiver R are fed to the grid of the C.R. tube as intensity modulation. The range of the apparatus is such that signals from reflecting objects occur during the first quarter of a cycle of the sinusoidal time-base deflecting wave and appear as bright spots on the radial line trace OM at distances from the centre O dependent upon the ranges of the objects. To measure range and bearing a transparent scale rule graduated in distance may be provided pivoted at the centre of the C.R. tube screen co-operating with a sector scale graduated in bearing. Alternatively adjustable range and bearing lines may be produced on the screen of the C.R. tube and employed to indicate the range and bearing of an object with the echo signal of which they are aligned. Production of bearing marker. The bearing line is produced under the control of unit C1 (Fig. 14), which comprises similar fixed coils B1, B1<1> fed with direct current and at the centres of which are the quadrature spaced secondary coils b1, b1<1> which rotate in step with the aerial radiation pattern. The 90 degree displaced outputs from the coils b1, b1<1> are fed to the stator coils 11, 11<1>, 12, 12<1> of a phaseshifting transformer DEPH1, and the variable phase output from the secondary coil 13 is amplified by the triode-pentode L3 and fed to the triode-pentode L4 which, by limiting and. successive differentiations by inductances 14, 16, Figs. 20-23 (not shown), produces narrow triangular pulses. These pulses are fed to one control grid of a mixer valve L6, the other control grid of which is fed with a positive pulse equal in duration to one quarter of the recurrence period, Figs. 25, 26 (not shown), obtained by feeding the output of the generator G via transformer 20 and the adjustable phase advance circuit 21, 22 to the amplifying and distorting valve L5. The variable condenser 21 is adjusted so that the positive pulse coincides with the utilized first quarter of a cycle of the sinusoidal time base sweep on the C.R. tube. The resultant output pulses from the mixer valve L6 thus comprise narrow pulses produced from the triangular pulses fed from valve L4 and of a width determined by the bias of L6. They are fed via valve L7 to intensity-modulate the C.R. tube so that one or more of the radial traces OM (depending upon the bias of L6 and resultant pulse width) is brightened to form a bearing marker, the angular position of which is controlled by the setting of the coil 13 of the phase-shifting transformer DEPH1. Production of range marker. A circular range marker, Fig. 28 (not shown), is generated on the C.R. tube by means of very narrow pulses at the recurrence frequency whose time of occurrence is adjustable over the duration of the sweep OM. The output from generator G is fed via a zero-adjusting phase-shift network 34, valve L8, and phase-splitting circuit 38, 39, 40, 42 to the stator coils of the rotating-field phase-shifting transformer DEPH2. The output from the secondary coil 44 is amplified and distorted by valves L9, L10 and circuits 46-51 to produce the sharp pulses which when fed to the grid of the C.R. tube produce the range circle of radius controlled by the setting of the phaseshifting transformer DEPH2 which is graduated in terms of range. Detection of aircraft. The aerials 1, 2 are arranged to scan in a vertical plane, Fig. 30, so that the phase shifters DEPH1 and 2 indicate the range and angle of elevation of a detected aircraft. To determine azimuth the aerials are mounted on a platform 3 rotatable by a motor M1 and a second cathode-ray tube indicator, Fig. 34 (not shown), is employed in conjunction with a unit similar to C, Fig. 19, and its associated circuits, to produce a timebase trace whose angular position corresponds with angular setting in azimuth of the aerial system. When the search is restricted to 180 degrees the transmitter and receiver may be separated from the aerials which are fed through rotating joints, Fig. 31 (not shown), but when continuous scanning in two planes is employed the transmitter and receiver may be mounted on the rotating platform 3 (Fig. 30). Specifications 627,749 and 627,750 are referred to.