GB889460A - Improvements in or relating to antenna array - Google Patents

Abstract

889,460. Radar; radio direction-finding; aerials. ALGEMENE NEDERLANDSE RADIO UNIE N.V. Dec. 9, 1959 [Dec. 11, 1958], No. 41937/59. Class 40(7). The invention relates to an aerial system for direction-finding and radar purposes which is suitable for automatic tracking and which avoids the received signal having a null value when the aerial system is correctly aligned on the target. The system comprises a centrally fed linear array of aerial elements connected as branches of a first "magic T" junction, the E and H branches of this junction being connected by waveguides to the similar branches of a second "magic T" to the output branches of which are connected identical amplifiers or detectors. In a simple embodiment comprising a slot array the two aerial array branches 1, 2, feed a junction having E and H branch outlets 3 and 4 respectively. These are connected to the corresponding branches 5 and 6 of a second junction whose arms 7 and 8 contain probes or detector crystals 9 and 10. The array may be either resonant or non-resonant. In either case an in-phase connection of the array sections, as by the H branch feeder, will provide a single main lobe pattern symmetrical about an axis perpendicular to the array. Out of phase connection of the two array sections, as by the E branch feeder, on the other hand provides a two-lobed pattern. with a null on the above mentioned axis. It should be noted that the pattern lobes on each side of this null are in opposite phase. The E branch coupling feeds outputs of opposite sign to detectors 9 and 10 whilst the H branch coupling feeds them with in-phase signals. For auto-follow purposes the detector outputs are subtracted and the resultant signal used to drive the motor aligning the aerial system. Provided the target is initially within the single lobe pattern to give an output over the H branch coupling tracking can be effected. For searching purposes the single lobe pattern may be broadened by providing micro-wave switches disconnecting the outer parts of the array. Communication is possible during tracking due to the finite (but equal) outputs from detectors 9 and 10. Aerial systems according to the invention may be used in point-to-point communication links and in radar systems. Fig. 3 shows an embodiment for radar use. In this the H branch coupling is considerably modified. The H connection 16 from the first junction leads past a short slot hybrid 22 to a T.R. cell 24 and on past a second short slot hybrid 25 to a matching impedance termination 26. The H connection 27 from the second junction is arranged parallel and includes hybrid 25, a second T.R. cell 23 and hybrid 22. It is terminated by connection to transmitter magnetron 21. A transmitter pulse causes T.R. cells 23 and 24 to fire and energy is directed through slot 22 to feed the aerial system sections in phase. Received signals are below the power necessary to cause the cells to fire and pass to the second "magic T" junction exactly as described for the previous embodiment. A klystron 28, or other source of hetrodyning radiations, may be coupled to the H branch of this second junction through a directional coupler 29. To protect detectors 19 and 20 during transmission a micro-wave switch 17, controlled by the transmitter modulating arrangement is inserted in the E branch connection. Fig. 4 shows an aerial system for determining bearings in spherical co-ordinates having two mutually perpendicular centre-fed arrays 30, 31, and 36, 37 coupled at different levels to a turnstile junction 32. In-phase signals from the array at the same level and out-ofphase signals from the other array are derived from pairs of outputs 33, 34 and 38, 39 and may be used to provide error signals for tracking.