Patent GB-855262-A (GB)
Title: Improvements in or relating to aerial systems
Inventor: MORAN MICHAEL JAMES
IPC: H01Q25/00
Filed: 1956-06-08
Abstract: 855,262. Aerials; radar. DECCA RECORD CO. Ltd. Sept. 9, 1957 [June 8, 1956], No. 17876/56. Class 40(7). The invention relates to an aerial system for use with Doppler airborne navigation equipment for the determination of the ground speed and drift of the aircraft. Such equipment requires an aerial system capable of radiating simultaneous narrow beams downwardly from the craft to the front to port and to the rear to starboard alternately with corresponding beams to the front to starboard and to the rear to port. In accordance with the present invention aerial system comprises two sets of rows of radiating slots, the slots in each row of one set being phased and those in the rows of the other set being in antiphase so that when the rows are arranged in the fore-and-aft direction on an aircraft one set will produce a forwardly directed beam and the other a rearwardly directed one and the phase relationships of the feeds to the rows of sets differing between the sets so as to produce opposite transverse deflections of the beams. In one embodiment of the invention the set of antiphase rows of slots 20 to 25 are arranged adjacent but separate to the in-phase set of rows 26 to 31. The first of these sets is fed from transverse waveguide 32 and the second from guide 33. As shown each of the feed guides is fed from the transmitter and receiver through switch 35 and power divider 36. The points of connection of the rows to the transverse guides are chosen, having regard to the wavelength of the energy in the guide, to produce the required deviations; one beam to port and one to starboard. To produce the alternate pair of beams the switch 35 is moved to the other position to feed the two transverse guides from their opposite ends through power divider 37. The couplings between the rows and the transverse guides are made symmetrical along the latter so that the switch causes the beam that was to port to be deflected through an equal angle to starboard and vice-versa. The deflection of the beams forwardly and rearwardly remains unchanged and the system operates equally well for transmission and reception. The switch 35 as shown is purely diagrammatic and a suitable practical switching system using four 3db directional couplers and a switch in two of the interconnecting waveguides is described with reference to Fig. 4 (not shown). In a modification of the embodiment of Fig. 2 (Fig. 5, not shown) the rows of slots of the two sets are interleaved instead of forming adjacent groups. Practical details of constructions of the embodiments of Figs. 2 and 5 are described with reference to Figs. 3, 6 and 7 (all not shown). In another embodiment of the invention the in-phase rows of slots 101 to 106 and the antiphase rows 111 to 116 are fed from the transmitter and receiver 122 through switch 123 and transverse waveguide 120. The phasing of the couplings along the guide 120 is arranged to give the deflections to port and to starboard required. To change to the alternate pair of beams the switch 123 is altered to energize transverse waveguide 121 at the opposite end of the slot rows. The rows of slots are made symmetrical about their centre points and the feed spacings along the guides 120, 121 are made the same so that alteration of the switch causes the port deflected beam to move from a forward to an equivalent rearward direction or vice versa and the starboard deflected beam to do the opposite change. In this embodiment the single transverse guides 120, 121 may be replaced by pairs of guides coupled to the switch through power dividers; one of each pair will then feed one set of rows and the other the other set in a way similar to that shown in Fig. 2. The use of a pair of transverse guides of different cross-section enables the physical spacing of the rows in the two sets to be made the same and is essential in an embodiment in which the two sets are interleaved. To obtain a small deflection to port or starboard alternate rows in the two sets must be fed in opposite phase from the transverse guides. The aerial may be stabilized either in the pitch plane only or completely. Specifications 837,091 and 855,263 are referred to.