Patent GB-600611-A (GB)
Title: Improvements in antennas
IPC: H01Q13/24
Filed: 1944-06-09
Abstract: 600,611. Aerials ; radiolocation. WESTERN ELECTRIC CO., Inc. June 9, 1944, No. 11126. Convention date, Nov. 4, 1942. [Class 40 (vii)] An ultra-high-frequency, multiple-unit, steerable antenna, particularly suitable fur a scanning radiolocation system, comprises a plurality of end-on units in a broadside array, the angular width of the maximum lobe of radiation from each unit being greater than the angular spacing between adjacent major lobes of the space-factor characteristic of the array (i.e. the radiation characteristic of the array assuming non-directional elements) and less than the angular spacing between alternate spacefactor major lobes. The array, shown in perspective in Fig. 1 and diagrammatically in Fig. 2, providing a narrow beam scanning over a 30 degrees sector for a radiolocation system, comprises fourteen antenna units 6 spaced apart along horizontal axis 2 a distance H of approximately two wavelengths, each unit comprising a vertical stack or " trident " of three unidirectional dielectric antenna elements spaced apart by a distance V of approximately 2.7 wavelengths. In each " trident '' the tapered antenna elements or polyrods 7 are connected through short circular wave - guides sections 14 and matching transformers 15 to rectangular waveguides 16, the three guides 16 being connected through a transformer and load distributer 17 to a trident waveguide 18. The fourteen " tridents " are devided into two sub-arrays, tridents A3, A2, A1, A0. A4, A5 and A6 constituting one sub-array and tridents B3, B2, B1, B0, B4, B5 and B6 constituting the other sub-array. The seven " trident " guides of each sub-array are connected to sub-array guides 9 and 10 respectively containing waveguide phase shifters C1-C6 and D1-D6, of the type described in Specification 575,577, connected in tandem, the central " tridents " being connected to the mid-points 19 and 20 of the sub-array guides. These mid-points are coupled together by an auxiliary wave-guide 21, the mid-point of which is coupled by coaxial line 4 to the radiolocation transceiver 5, a phase-changer 22 being inserted in the connection to sub-array guide 9. Impedance matching plungers are provided near the " T " and " X " junctions 25 and 24 to match the input impedances of the junctions to the. guides 9 and 10, transformers 27 being provided to match the impedance of the circular guides forming the phase-changers to the adjacent rectangular guides. By adjustment of the wave-guide apertures at the junction points, the intensities of the waves supplied to the " tridents " in each sub-array are adjusted to have a stepped triangular power distribution for the whole array as shown by the lengths of arrows 28 in Fig. 2. Phase-changers C and D are all rotated at the same speed by the twospeed motor 31 through gearing 33, shafts 34 and gears 35 and 36 and phase-changer 22 is driven by gearing 37, 38 at half this speed, the phase-changers C and D thus producing a phaseshift of 2# each, while the shift of # is produced between the sub-array by phase-changer 22. In order to equalize the phase delays (neglecting the phase-shifters) for all fourteen " tridents," loops 30 are provided in the guides feeding all tridents except those at the ends of the subarrays. The relative phases of the waves at each " trident " are, for a shift # produced by phase-shifter 22, as shown in Fig. 2, a phase difference of # existing between adjacent "tridents." The space-factor characteristic of the array in the horizontal plane is indicated at 126, Fig. 8, and comprises relative narrow major lobes 127, 128 and 129 spaced at 30 degrees intervals and minor lobes 130, the primary lobe 127 being shown as on the axis 3 perpendicular to the plane of the array. When a phase displacement is produced between the waves in adjacent " tridents," the space factor diagram effectively rotates and when the phase displacement between'adjacent " tridents " has changed by 360 degrees, the next major lobe will be aligned with the axis 3. If each " trident " element had an ideal characteristic such as 131, in the horizontal plane, which has an angular width of 30 degrees, the resultant overall directive characteristic would comprise only one major lobe which would scan continuously across a 30 degrees sector in one direction as the phase-shift was continuously varied, one sweep or scan occurring for each rotation of motor 31 and phase-shifters C and D. The actual horizontal " trident " characteristic is as shown at 115, Fig. 8, and includes the maximum lobe 121, nulls 122 and 123 and minor lobes 124, 125. The resultant overall characteristic for the array is shown at 139, Fig. 10, comprising a principal lobe 140 and subsidiary lobes 141, lobes 142 being negligible. Due to the fact that the actual " trident " characteristic is more than 30 degrees wide, the scanning is only unambiguous over the central sector of the 30 degrees scan extending from +7.5 to - 7.5 degrees. As the major lobe 127 of the space factor diagram moves to the left between the - 7.5 degrees position and the null 123, the secondary lobe 128, which is about to become the primary lobe, climbs up the " trident " lobe 115 between the +22.5 and +15 degrees directions and produces a resultant lobe in that direction giving ambiguous bearing indications. Radar system and displays. The transceiver 5 comprises a conventional T.R. box 39 connected to line 4 and supplying to and receiving from the array, pulsed centimetre waves. Echo signal outputs from the receiver are fed through lead 45 and switch 44, which conditions the equipment for a class A or class B type of signal display, to the vertical deflecting plates or the grid 52 of the C.R. tube 40. The reference pulse from the transmitter is fed through an adjustable liquid delay device 41 to a stepping circuit 43 producing a range marking step wave which is fed through switch 44 in the class A position to the vertical deflecting plates of the C.R. tube. The reference pulse is also fed directly via lead 46 and switch 44 in the class B position to the grid of the C.R. tube to produce a bright range marker on the class B display. The delay device 41 is adjusted by a handle 49 and gearing 51 and the range may be determined by a counter 52 when the range step or marker is aligned with a target echo. A saw-tooth generator 63 controlled from the transmitter over lead 64 provides the time base for the class A display, which is fed via lead 65 and switch 44 to the horizontal deflecting plates of the C.R. tube. A similar saw-tooth generator 66'provides the time base which is fed via lead 68 and switch 44 to the vertical deflecting plates of the C.R. tube to produce the class B display. To produce the transverse displacement of successive time base traces, corresponding to the scanning of the radiated beam, in the class B display, a saw-tooth generator 69, timed by the rotating contact 72 driven at the speed of the motor 31, is connected through switch 44 to the horizontal deflecting plates of the C.R. tube. For class B operation, the motor 31 is run at high speed producing 600 sweeps per minute, while for class A operation the motor is run at low speed to produce only one sweep or scan per minute so. that targets on a particular bearing may be observed on the horizontal time base for searching purposes. In order to provide vertical bearing indicating lines on the class B presentation, an insulating disc 78 with radial conducting arms 81-85 which is rotated at the speed of the motor 31, is arranged to co-operate with contact 88 and provide a voltage which is fed through lead 89 and switch 44 to the grid of the C.R. tube to brighten the time base traces occurring as the scanning lobe occupies the 0 degrees, Œ5 degrees and Œ10 degrees azimuth angle position. The bearing of a target may thus be roughly determined by observing the position of its echo with respect to the azimuthal angle lines. For more accurate determination, the whole antenna may be rotated about the vertical axis on shaft 93, thus shifting the 30 degrees scanning zone until the centre of the echo coincides with the zero angle line. The counter 52 and the shaft 93 supporting the array may have connected to them through gearing 103 voltageproducing arrangements comprising servomotors, voltage sources and potentiometers, whereby voltages representing range, and bearing are obtained which may be fed to a computer-predictor system. Specifications 487,716, 501,966, 526,658, 543,299 and 600,604 also are referred to.