GB599497A - Improvements in or relating to electrical arrangements for connecting two sources totwo loads - Google Patents

Abstract

599,497. Impedance networks; radio direction-finding. WESTCOTT, C. H. Jan. 9, 1945, No. 788. [Classes 40 (iii) and 40 (v)] A balanced bridge composed of four quarterwave transmission lines serves to connect two aerial arrays to two senders or receivers in such a way that two different polar diagrams are alternately effective ; or to two receivers whose demodulated outputs are combined in opposition to give the effect of a narrow beam. In a radar aerial system two arrays A1, A2 and A4, A5, are connected to opposite corners B, D of a network composed of quarter-wave lines, and the legs are crossed at E to give a reversal of phase. The corner E is connected to a feeder Q, and the remaining corner C to a feeder P and a central aerial A3. The system is so dimensioned that power from the feeder P, when the system is used for sending, reaches all the aerials in equal amplitude and phase, but owing to the crossing of the legs of E, power from the feeder Q reaches the arrays A1, A2, and A4, A5 in antiphase and does not reach the aerial A3. The resulting polar diagrams are complementary to one another, Fig. 4 (not shown). The impedance presented to the feeder P is independent of that presented to the feeder Q, provided that the system is symmetrical. When the system is used for receiving, two receivers are connected to the transmission lines P, Q, and their demodulated outputs may be combined in opposition, Fig. 2 (not shown), the effective beam-width being thereby reduced in the resultant polar diagram, Fig. 6 (not shown) ; for instance when the invention is applied to a radar system of the kind described in Specification 582,494, so as to narrow the indications on the cathode-ray tube of the bearing indicator and to reduce noise as a result of the resultant demodulated signal giving off bearing. The 5-bay in-phase aerial system may be used in the radar sender, and the overall polar diagram for this combination is given in Fig. 8 (not shown). Alternatively the line Q may be connected to the sender and one receiver while the other receiver is connected to the line Q, a protective transmitter-receiver switching device of the kind described in Specification 583,743 being provided. In a friend-or-foe interrogator system of the kind described in Specification 585,347 the invention may be used to eliminate off-bearing responses. In a common-aerial system the invention may be used in conjunction of a transmitter-receiver switch and a balanceto-unbalance matching device for combining the high-frequency outputs of the lines P, Q, Fig. 3 (not shown). Specification 582,521 also is referred to.