Patent GB-589608-A (GB)
Title: Radiated-signal receiving system
IPC: G01S1/02
Filed: 1944-09-26
Abstract: 589,608. Directive radio signalling. HAZELTINE CORPORATION. Sept. 26, 1944, No. 18415. Convention date, Oct. 27, 1943. [Class 40 (v)] A receiving system with a sharply directive response characteristic which is variable in direction, comprises an array of spaced aerial elements, the signals from each aerial. being individually modulated, each with a different frequency so that predetermined ones of the modulation components have additive phase for only one direction of reception which varies continuously and periodically over an angular range and at a rate determined by the separation of the elements of the array and the frequency separation between the modulating waves. The directive receiving system of Fig. 2 comprises a linear array 10 of five equally spaced elements 11-15 associated with separate modulators 16-20. Individual modulating signals, equally spaced in the frequency spectrum, for application. to the modulators 16-20 are obtained by first modulating a subcarrier frequency f<1>o from generator 33 with harmonically related frequencies fh and 2fh from oscillators 36, 37, in the modulator 38. Tuned transformer 45 selects the carrier frequency component in the output of modulator 38 while transformers 41, 43, 47 and 49 select respectively the lower and upper sideband components corresponding to the frequencies fh and 2fh. These components are applied separately to modulators in units 42, 44, 46, 48 and 50 which are also supplied with heterodyne oscillations #o<SP>11> from oscillator 56. The resultant sum-frequency components are selected by band-pass selectors in the units 42, 44, &c., and comprise together the carrier and sideband components of a carrier #c modulated with frequencies fh and 2fh. These carrier and sideband components are fed separately to the modulators 16-20 and the difference-frequency components in the outputs of the modulators which are selected and amplified by units 26- 30 before combination, comprise the components of an intermediate frequency #c-#o, where #c is the received signal, modulated with frequencies fh and 2fh. The frequency relation of these signals is such that the system has effectively a sharply directive response which scans at a frequency determined by the difference frequency fh between the modulating signals associated with adjacent aerials, the velocity of scanning depending also upon the spacing of the aerials. The rate of scanning may therefore be varied by adjustment of the frequencies of oscillators 36 and 37 and slight retuning of the transformers 41, 43, 45, 47 and 49, readjustment of the selectors of units 42, 44, &c. not in general being necessary due to the broader band at the higher frequencies. The configuration of the major lobe of the scanning beam may be changed by control of the relative amplitudes of the modulating signals produced by units 42, 44, &c. by suitable adjustments of the relative amplitudes of the components generated by oscillators 36, 37 or the depths of modulation produced by units 42, 44, &c. The output signals from units 26-30 which are in phase, combine and provide the input signal to the unit 31<1> where they are amplified and detected and the lowfrequency signal, which is in the form of a pulse produced by the co-operation of the scanning directive characteristic and a relatively fixed source of received signals, is further amplified. The received pulse signal is fed to produce intensity modulation of the cathoderay tube 57, the deflecting electrodes 60 of which are fed with a saw-tooth scanning voltage from generator 59 synchronized from oscillators 36, 37. The position of the spot indication on the trace thus indicates the direction of the source of the received signals from the receiving system, the delay network 58 ensuring that the centre of the trace corresponds to directions normal to the receiving array. In a modification, Fig. 3 (not shown), an array of six equally-spaced aerials is employed, the signals from the two centre aerials being modulated with waves of #o+#h /2 and #o- #h/2, the signals from the intermediate and outer aerials being modulated with waves displaced 3#h/2 and 5#h/2 above and below #o respectively. These waves are produced by modulation in carrier suppression modulator with frequencies fh/2 , <3>fh/2 and <5>fh/2. In a further modification, Fig. 4, which comprises essentially a number of systems similar to that illustrated in Fig. 2, a bank of aerial elements comprising a number of linear arrays such as 11-15 is arranged to have a directive characteristic which scans in two perpendicular dimensions. A modulation signal generator 69 producing frequencies fv and 2fv and a subcarrier generator 33 of frequency fc feed a modulator 70, the resulting carrier and sideband components being separately selected by band-pass selectors and modulators such as 38 and each component being separately modulated with frequencies fh and 2fh from the generator 36, 37. The products of this second modulation of each of the first components, comprising carrier and upper and lower sidebands are separated by further band-pass selectors and modulators such as 42, 44, 46, 48 and 50, which select the carrier and sidebands resulting from the modulation of the carrier frequency component of the first modulation products, and are heterodyned by a frequency fo from the oscillator 56, the individual resultant difference frequencies being selected and fed to appropritate modulators such as 16-20 associated with the receiving aerials. The modulating waves fed to adjacent modulators in any of the horizontally disposed arrays have a difference frequency fh while corresponding modulators in adjacent arrays are fed with modulating waves differing in frequency by fv so that the directive characteristic scans horizontally at a rate determined by fh and in a vertical direction at a preferably lower rate determined by fv, the resultant scanning pattern being one of parallel lines which may be interlaced. The output signals from all the modulators associated with the receiving aerials are combined in a common intermediate frequency channel and fed to the receiver unit 31', the output of which is displayed as intensity modulation on the oscillograph 57 which is provided with horizontal and vertical scanning by oscillators 59 and 71 which are synchronized with the modulation signal generators 36, 37 and 69 through the delay networks 58, 73. Specifications 577,672, 577,674, 589,607 and 589,609 are referred to.