. Airborne radar. Airplanes; Guided missiles. 10-19] DUPLEXING SCHEMES 571 tion, taking advantage of the directional characteristics of the antennas. Seldom is this a very practical solution in airborne systems. The method requires two separated antennas located where space and weight are at a premium; it poses problems of interconnection, as well as problems of alignment and parallax between the antennas. A preferred solution is to employ some duplexing device or circuitry which permits use of a common antenna for simultaneous transmission and reception. There are several linear duplexing sch
. Airborne radar. Airplanes; Guided missiles. 10-19] DUPLEXING SCHEMES 571 tion, taking advantage of the directional characteristics of the antennas. Seldom is this a very practical solution in airborne systems. The method requires two separated antennas located where space and weight are at a premium; it poses problems of interconnection, as well as problems of alignment and parallax between the antennas. A preferred solution is to employ some duplexing device or circuitry which permits use of a common antenna for simultaneous transmission and reception. There are several linear duplexing schemes which might be used in certain applications; however, in general they involve a two-way trans- mission loss of 6 db. Any of the familiar 3-db hybrid junctions can be employed in a linear balanced duplexer^^ as illustrated schematically in Fig. 10-43. The transmitter is shown connected to port 1 of a hybrid ring Dummy Load Transmitter. Ring Hybrid Fig. 10-43 Linear Balanced Duplexer Using Ring Hybrid. which divides the power equally between arms 2 and 4. The receiver is connected to arm 3 and will be isolated from the transmitter on arm 1 if arms 2 and 4 are properly terminated. As with any linear duplexer, antenna mismatch will cause direct reflection of transmitter power back to the receiver. This reflected component- can be canceled out by an adjustable reactance in arms 2 or 4, but a very frequency-sensitive duplexer may result. To achieve a high degree of isolation between transmitter and receiver in a duplexer of this type the hybrid must be well balanced and the antenna and dummy load well matched. The 6-db loss arises in this type of duplexer because half the transmitter power is "dumped" in the dummy load and only half the received power reaches the receiver. Linear duplexing can also be accomplished using ynode multiplexing techniques. Thus orthogonal linearly polarized modes are employed, for example, in circular or square waveguide, transmitting on one
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