GB794441A - Improvements in or relating to duplexers - Google Patents

Abstract

794,441. Duplex radio signalling. DECCA RECORD CO., Ltd. June 13, 1956 [July 5, 1955], No. 19458/55. Class 40 (5). Relates to duplexers for microwave systems having a common transmitting and receiving antenna. In one embodiment a pair of hybrid units 14 and 15, Fig. 1, whose arms are numbered 1 to 4, are interconnected by their third and fourth arms, a phase shifter 17, which may be a gyrator, being connected between their third arms, enabling the electrical effective length of these connections to be altered by half a wavelength according to the required direction of signal transmission through the duplexer, the connection being such that an input at arm 1 gives an equal output at arms 3 and 4 and no output at arm 2. The transmitter 12 and receiver 13 are connected to arms 1 and 2 respectively of unit 14, arms 1 and 2 of unit 15 being terminated in the antenna 10 and a matched load 16. A second phase shifter may be connected between the fourth arms. A duplexer for pulse radar systems, Fig. 2, uses four hybrid units 14, 15, 20, 25, with gas cells 23 and 24 a quarter wave in front of, and terminated by short circuits 21 and 22, arranged in arms 1 and 2 of hybrid unit 20. The gas cells fire on application of a transmitter pulse to the circuit thus changing the electrical length of the connections between the third arms of units 14 and 15 by a half wavelength. The two gas cells may be embodied in a single gas tube. Another embodiment uses 3 db. branched-guide directional couplers as hybrid units and a single gas cell, Fig. 3 (not shown).