Patent GB-589609-A (GB)
Title: System for locating a radiated-signal reflector
IPC: B65H29/14
Filed: 1944-09-26
Abstract: 589,609. Radiolocation. HAZELTINE CORPORATION. Sept. 26, 1944, No. 18416. Convention date, Oct. 27, 1943. [Class 40 (v)] A radiolocation system comprises a transmitting aerial array, the spaced elements of which are fed with individual waves having incremental frequency differences so that the radiated beam angularly scans a predetermined space and a'receiving array, the spaced elements of which feed individual modulators which are also fed with modulating waves spaced in frequency so that predetermined ones of the resulting modulation products are in phase for one direction of reception only which scans in synchronism with the radiated beam. The radiolocation system of Fig. 1 comprises essentially a transmitting arrangement similar to that described in Specification 589,607 and a receiving arrangement similar to that described in Specification 589,608. The scanning control generator 21 feeds frequencies fh and 2fh to the modulator 23' which is fed also with a sub-carrier of frequency fc from the generator 22. The carrier and individual sideband components in the output of modulator 23 are separated by band-pass selectors in units 25-29 and are heterodyned by a frequency fo from oscillator 30 to a frequency suitable for radiation, the sum-frequency terms being selected in units 31-35, amplified and fed to the equally-spaced radiators 11-15 of the array 10a to produce the beam of carrier frequency fo+fc which scans through substantially 180 degrees from radiator 11 towards radiator 15 at an angular frequency #h. Reflected signals are received by the array 10b, the signals from each of the spaced elements 16-20 being separately fed to modulators 45-49. To cause selected modulation products in the outputs of these modulators to have additive phase for a direction of reception which scans in synchronism with the transmitted beam, a modulator 36 is fed with the sub-carrier fc and the scanning frequencies fh and 2fh, the carrier and sideband components being separated in units 39-43 and raised to higher frequencies by the heterodyne oscillation fo from oscillator 44 before being fed as the modulating signals to modulators 45-49. The difference frequency terms in the outputs of modulators 45-49 are selected and amplified in units 51-55 and the combined output fed to the I.F. amplifier 56 to produce a directive response of the array 10b which scans in synchronism with the radiated beam from array 10a. The intermediate frequency output which is of pulse form, due to the directive patterns scanning across the reflecting object, is rectified at 57, amplified at 58 and fed to intensity modulate the cathoderay tube indicator 59 which is provided with a time base by the saw-tooth scanning oscillator 60. Oscillator 60 is synchronized from the scanning control generator 21 via a delay network 61 so that the time base commences when the scanning beams extend in the direction of alignment of the array. To allow for the time delay of the reflected signals, when the scanning rate is high, an adjustable phase shifter 37 may be employed to delay the modulating signals fed to modulator 36 and thus cause the scanning of the directive-response characteristic of array 10b to lag that of array 10a. The adjustment of phase shifter 37 for maximum response may thus beemployed as an indication of range and the phase shifter may be continuously adjusted so that indications of near and distant objects may be obtained in sucesssive groups of scanning cycles. If pulse modulation is employed, as described in Specification 589,607, the array 10a may be used for both transmission and reception if suitable lengths of line are employed for coupling the aerial elements to the amplifiers 31-35 and modulators 45- 49. The pulse modulation potentials may also be applied to the receiver through a delay network to increase the sensitivity during reception. In a, modification of the system described, Fig. 2 (not shown), the arrays 10a<1> and 10b<1> each contain six elements, the waves fed to the transmitting elements and also as modulating signals to the receiver modulators correspond to the sidebands only produced'by modulation with scanning frequency terms fh/2, 3fh/2 and 5fh/2. The modulator 36 and phase shifter 37 are also omitted and the lower sidebands are produced by the modulators of units 25-29 &c. are selected to provide the modulating signals for the receiver modulators. In a further modification, Fig. 3 (not shown), the spurious minor lobes, of the transmitting array 10a, are arranged to intervene between the minor lobes of the receiving array 10b". Array 10a is similar to the corresponding array of Fig. 1, but the central aerial element 13 is fed with signals of amplitude 2.25 times that of the signals fed to the other elements of the array and the resultant directional-radiation characteristic is shown at A, B and C, Fig. 4, at three intervals during a scanning cycle. The array 10b<11> contains only four elements, the central element 18 of Fig. 1 being omitted and produces the characteristic shown at D, E and F, the minor lobes of which fall within the gaps in the characteristics A B and C. The invention may be applied to scanning in two dimensions as described in Specifications 589,607 and 589,608. Specifications 577,672 and 577,674 also are referred to.