GB926343A - Microwave duplexer - Google Patents

Abstract

926,343. Directional couplers. ASSOCIATED ELECTRICAL INDUSTRIES. March 14, 1962 [March 15, 1961], No. 9504/61. Class 40 (8). [Also in Group XL (c)] A microwave duplexer includes a pair of 3 db. directional couplers 1, 2, a receiver R and transmitter T being connected to waveguides 3 and 4. respectively, of coupler 1, and an aerial A and non-reflective load 29 being connected to waveguides 5 and 6, respectively, of coupler 2. A further 3 db. directional coupler 7 has one waveguide 10 connected through an E-plane bend 11 to waveguide 9 of coupler 1, and the other waveguide 16 connected through an E-plane bend 17 to waveguide 15 of coupler 2. Similarly, a 3 db. directional coupler 8 is connected through an E-plane bend 14 to coupler 1 and through an E-plane bend 20 to coupler 2. Waveguides 21 and 22 of coupler 7 are coupled to a mounting 23 containing two gas discharge tubes, one in each waveguide, arranged in front of short-circuit reflectors 24, and a similar mounting 27 of coupler 8 carries two gas discharge tubes arranged in front of short-circuit reflectors 28. For low-power energy received by aerial A the gas tubes do not fire and the difference in the lengths of the two transmission paths through couplers 7 and 8, respectively, is such that signals reflected from reflectors 25 lag in phase by 90 degrees at end 12 of coupler 1, the signals appearing at end 9 of coupler 1 after reflection at 24. Since the coupler produces a further lag of 90 degrees in energy passing from one arm to the other the signals combine in phase at the receiver waveguide 3 and are cancelled in the transmitter waveguide 4. Energy from the transmitter T will cause the gas tubes to fire and in this case signals at 18 have a 90 degrees phase lead on signals at 15 and due to the 90 degrees lag produced by the coupler 2 the signals will combine in phase in the aerial waveguide 5.