Patent GB-589607-A (GB)
Title: System for space-scanning with a radiated wave-signal beam
IPC: G01S1/02
Filed: 1944-09-26
Abstract: 589,607. Directive radio systems. HAZELTINE CORPORATION. Sept. 26, 1944, No. 18414. Convention date, Oct. 27, 1943. [Class 40 (v)] A system for scanning a predetermined space with a beam of radiation comprises an array of spaced radiating elements which are individually fed with signal waves of different frequencies, the frequency differences between the waves applied to the radiating elements being related to the desired rate of scanning. If the array consists of equally spaced linearly disposed elements, the frequency difference between adjacent elements is constant so that the applied signals are equally spaced in the spectrum and increase in frequency in the order of spacing of the radiating elements from one end of the array. In the embodiment of the invention shown in Fig. 14, the array 10 comprises dipole elements 11-15 which may be horizontally aligned and are spaced by half a wavelength at the nominal operating frequency. A generator 30 of frequency fc provides the carrier input via transformer 29 to the balanced modulator 50, while modulation inputs of frequency fh and 2fh produced by the synchronized oscillators 33, 34 are fed via transformers 32 and 31. One cycle of the lower modulation frequency is represented by curve B, Fig. 2, while two cycles of the higher modulation frequency are represented by curve C and the unmodulated carrier level by curve A, so that curve D represents the envelope of the resultant modulated carrier. The carrier output component from the modulator is selected by tuned transformer 42, is heterodyned with frequency fo from oscillator 65 in modulator 57 and the upper resultant sideband fo+fc is selected in the filter-amplifier unit 68 and fed to the centre radiating element 13. Similarly, the upper and lower sidebands produced by the modulating frequences fh, 2fh are selected separately by the transformers 40, 41, 43, 44 and heterodyned with frequency fo in modulators 55, 56, 58 and 59, the frequencies selected by units 66, 67, 69, 70 being such that the outer radiators 11, 15 are fed with frequencies respectively below and above the nominal carrier frequency of fc+fo by an amount 2fh, while, the radiators 12 and 14 are fed with frequencies similarly disdisplaced by amounts fh. A graphical construction illustrated in Fig. 2, allowing for the physical spacing a of the radiating elements in wavelengths, enables the resultant radiation diagram of the system to be determined for any value of #ht, and three radiation diagrams F, G and H are shown. The major lobe of the diagram performs one complete scan from right to left for a change in #ht of 2# ; that is once for each cycle of the difference frequency fh. In a modification, Fig. 15 (not shown), producing a sharpened major lobe, six evenly spaced radiators are employed and the sub-carrier of frequency fc is modulated in a carrier suppression modulator with three terms of frequency fh / 2, 3fh / 2 and 5fh / 2. The inner radiators, each spaced from the centre of the array by half the spacing between adjacent radiators, are thus fed with frequencies displaced above and below the nominal carrier frequency by fh/2 while the frequency difference between any adjacent elements in the array is fh. The directional characteristics illustrated in Fig. 2 assume the radiators to be point sources and the true directional characteristic in a particular plane is obtained by modifying the characteristic of Fig. 2 in accordance with the appropriate coefficient of directivity of the radiators. The single dipole elements may have directors or reflectors associated with them to obtain enhanced directivity in the desired direction. Decrease of the spacing measured in terms of wavelength, between elements of the arrays either by change of the physical spacing or by change of the nominal, i.e. mean, carrier frequency, tends to broaden the major lobe of radiation, Figs. 9 and 11 (not shown), while increase of the electrical spacing results in sharpened lobes and the production of more than -one major lobe, Figs. 11 and 12 (not shown). A directional characteristic which during a scanning cycle comprises only a single concentrated major lobe free from side lobes, may be obtained by an array comprising a sufficiently large number of spaced radiators fed with individual waves which form the component waves of carrier modulated with a narrow rectangular pulse wave, as indicated in Fig. 13 (not shown). Fig. 16 illustrates a modification of the invention for scanning a radiated beam in two' directions normal to each other, which comprises a plurality of systems equivalent to that shown in Fig. 14. A wave of frequency fc from generator 30 is modulated with vertical scanning frequencies fv and 2fv from source 79 in modulator 80. The carrier and each sideband component in the output of modulator 80 is separately selected by one of the band-pass selectors and modulators such as 50, to which are applied the horizontal scanning modulating waves of frequencies fh and 2fh from the generator 51. Each component produced by the modulation with frequencies fh and 2fh of .each carrier or sideband component from modulator 80 is separately selected by one of band-pass selectors and modulators such as 40 55 and 41, 56, hererodyned with frequency fo from oscillator 65 and fed individually to the band-pass selectors, and amplifiers such as 66-70 and their associated radiating elements 11-15. The radiating elements are grouped into arrays such as 11-15 which together form a bank of arrays, corresponding elements in the arrays being arranged in columns. The radiators in each array are thus fed with waves which increase in frequency from left to right, the difference between adjacent elements being fh, while the frequency difference of the waves fed to any adjacent elements in a column is fv. The resultant radiation characteristic thus scans simultaneously in a horizontal direction at a preferably high rate and in a vertical direction at a preferably low rate. The scanning system may be operated with a pulse modulated transmission, the pulse recurrence frequency being so chosen that the major lobe scans in a number of discrete steps as it scans through 180 degrees, or if the period between pulses is long, the lobe may be produced only once during each scanning cycle, but its position may change during successive scanning cycles. With the latter mode of operation, a low effective rate of scanning may be produced when the actual scanning frequency #h is high. Specifications 577,672, 577,674 and 589,609 are referred to.