Patent GB-661081-A (GB)
Title: Radio apparatus for scanning a sector of space
IPC: H01Q3/22
Filed: 1945-07-19
Abstract: 661,081. Directive radio systems. SPERRY GYROSCOPE CO., Inc. July 19, 1945 [July 19, 1944], No, 18572/45. Class 40 (vii). An aerial system for rapidly scanning a sector of space at a recurrence frequency fo comprises a plurality of fixed aerials having different directivity characteristics which are energized by a carrier f and a plurality of side bands (fŒmfo) where m is any integer. In one form of the invention, Figs. 4, 7, 8 and Figs. 1-3, 5 and 6 (not shown), each aerial has a narrow lobe directivity characteristic and the aerials are arranged so that the lobes are angularly spaced with adjacent lobes partially overlapping, Fig. 1 (not shown), and are energized sequentially by time-displaced trains of rectangular wave pulses of recurrence frequency f o , Fig. 2 (not shown), which are synthesized by combining the carrier and side bands after passing them through separate phase and amplitude adjusters, Fig. 6 (not shown). In order to improve the continuity of scan, the pulse trains applied to adjacent aerials are arranged to partially overlap in time and the pulses may be of cosine-squared form, Fig. 3 (not shown), in which case fewer component frequencies are required. If an oscillatory scan is required the pulse trains may be such that the aerials are energized in one sequence from first to last and then in reverse sequence the cycle being repeated, Fig. 5 (not shown). Since the frequency components of the different pulse trains differ only in phase, common amplitude adjusters 22, Fig. 7, may be used, the phases of the components being adjusted by tapping off the conductors 32-34 leading to the combining circuits 23 at spaced points on the transmission lines 31. As shown, the frequency components are produced by modulating non-sinusoidally at 63 a carrier f from 61 with a frequency f o  from 62, and separating the modulation products in filter 64. In a modification, Fig. 8, the transmission lines 31<SP>1</SP> are bent into semi-circles connecting the amplitude adjusters corresponding to upper and lower side bands of equal order and the conductors leading to the combining circuits are radial lines 39-43 spaced at angles y dependent on the phasing of the pulse trains. Separate amplifying or buffer stages may be inserted between the respective taps of conductors 39-43 to compensate for any phasing errors. The aerial system may comprise a number of wave-guides 51-55, Fig. 4, radiating into a wide-aperture cylindrical-parabolic reflector 28, the lobe produced by the central wave-guide 53 being along the axis of the parabola and the lobes produced by the other wave-guides being angularly disposed to the axis. To produce a conical scan the waveguides are disposed about an imaginary cylinder whose axis coincides with the axis of a paraboloid. The second form of the invention, Figs. 9-19 (not shown), is based on an analysis which shows that a beam may be scanned at a recurrence frequency f o  by radiating a carrier f and side bands (fŒmf o ) of suitable amplitude and phase from separate aerials having directivity characteristics of different shape but with the same axis of symmetry, each aerial radiating one frequency component only. The Specification shows that each aerial should be designed so that the field intensity at a point in its aperture distance x from the centre of the aperture is proportional to the product of the Fourier transform of the static directivity characteristic of the beam expressed as a function of X where X=x/# times a Bessel function of argument proportional to X and to the angular scanning swing and of the same order as the order of the sideband applied to that particular aerial. The required field intensity may be produced by suitably distorting a parabolic reflector or by using a rectangular horn, Fig. 16 (not shown), with vanes dividing it into sectors, dielectric material being inserted in some of the sectors to produce any required phase reversal. The intensity distribution for the odd order side bands is of opposite phase in the two halves of the aperture and this may be produced by using two contiguous horns excited in phase opposition, Fig. 15 (not shown), or by using a single horn with a central partition the two halves being excited in phase opposition. The Specification as open to inspection under Sect. 91 states that an aerial system as used in the first form of the invention may be employed for transmission or reception by rendering the aerials sequentially operative by electronic switching means and it is also stated that the embodiments of the first form of the invention as described above may be used for reception by connecting the outputs of the frequency component filters, e.g. filters 64 in Fig. 7, to a suitable combining circuit to which the receiver is connected. This subject-matter does not appear in the Specification as accepted.