Patent GB-813934-A (GB)
Title: Improvements in or relating to aerial systems
Inventor: BECK GEOFFREY EDWARD
IPC: H01Q25/00
Filed: 1956-09-26
Abstract: 813,934. Aerials; radar. MARCONI'S WIRELESS TELEGRAPH CO. Ltd. June 27, 1957 [Sept. 26, 1956], No. 29384/56. Class 40 (7). [Also in Group XL (b)] Aerials.-An aerial system capable of providing two differently directed radiation patterns comprises a slotted waveguide radiator having a slot pattern which is the same whichever end of the waveguide it is viewed from, means for connecting either end to a feeder, and means for providing a non-reflecting load at the end opposite the feeder. A simple form of radiator which can be used is one in which parallel slots are cut at a constant angle to the transverse cross-section in one of the narrow faces of a rectangular guide. All the slots are cut to be of #/2 folded length. Fig. 6 shows a more complex radiator in which the angle of the slots to the transverse cross-section of the rectangular guide is greatest in the centre of the slot array and decreases symmetrically to either side. The change in the slot angle is in the same direction viewed from either end of the guide. The folded length of each slot is still #/2 so that the outer slots are cut deeper as shown in Fig. 7 which is a schematic representation of a complete system. In this a transmitter 8 feeds the radiator through a switch 9 which may be positioned to feed energy to one of the two ends of the radiator and to connect a load 10 or 10<SP>1</SP> to the unfed end. In one position of the switch radiation is in the direction of the arrow making the angle A1 with the perpendicular to the slot plane whilst in the other switch position it is in the direction of the arrow making the angle A2. So far it has been assumed that a set of in-phase slots only is cut in the radiating guide; it is, however, possible to have an intercalated second set of slots in anti-phase to the first and this second set of slots should also form the same pattern from whichever end they are viewed. Another form of radiator may, therefore, consist of a guide with a set of parallel in-phase slots intercalated with a set of parallel anti-phase slots (Fig. 8, not shown). Phase and anti-phase sets of slots may also vary in cut angle as described with reference to Fig. 6 to produce a radiatior of the form indicated in Fig. 9. Radar.-Aerial systems as above described may be used in radio speed and drift measuring apparatus for aircraft of the type in which energy is transmitted downwards and simultaneously forwardly and to port and aft to starboard or aft to port and forwardly to starboard. A measure of the speed and drift is forwardly to starboard. A measure of the speed and drift is obtained in such apparatus from the Doppler shifts in the reflected energy received back at the craft. By using one aerial system according to the present invention for the alternate starboard transmissions and another for the port transmissions the number of aerials required is reduced. In a preferred embodiment (Fig. 10), one of the transmitting aerials 22 has in-phase and antiphase sets of slots whilst the other 23 has an in-phase set only. They are fed from the same transmitter 26 through simultaneously operated switches 24 and 25 giving one forward and one rearwardly directed beam. The receiving aerial 27 may be of the same type with widely spaced slots so that it is capable of receiving reflected energy derived from any of the four transmitted beams. This aerial is switched in synchronism with the transmitting aerials by switch 28 in the connection to receiver 29. This particular arrangement of aerials is stated to give a high degree of immunity from undesired shifts of frequency resulting from the effect of temperature changes on the radiating system. An unswitched receiving aerial and two transmitting aerials of the same kind could, however, be used,