Patent GB-847830-A (GB)
Title: Improvements in or relating to microwave duplexer-switching systems
IPC: H01P1/11
Filed: 1957-02-13
Abstract: 847,830. Waveguide circulators. MONOGRAM PRECISION INDUSTRIES Inc. Feb. 13, 1957. [Feb. 23, 1956], No. 4893/57. Class 40(8). [Also in Group XL(c)] A double throw microwave switch and duplexer comprises a four arm circulator incorporating a ferrite element and reversible polarizing means, whereby a standby transmitter or receiver equipment can be brought into service on failure of the main apparatus or apparatus may operate into or from two antennas. I Operation of the circulator. A reversible four arm circulator 1 Fig. 1 comprises two short lengths 3 and 5 of rectangular waveguide, positioned edge-to-edge, joined at each end by short-slot hybrid junctions 7, 7<SP>1</SP> Protruding longitudinally by one eighth of the short width of and into waveguide 3, are narrow ferrite slabs 9, each secured to one pole piece of the core 11 of an electromagnet with energizing coils 13 to form a gyrator. Extending through guide 5 is a polystyrene compensator 15 which loads the waveguide section by so increasing its capacity as to advance the phase of a wave propagated through it by 90 degrees plus the phase-advance in guide 3 resulting from the loading due to the ferrite slabs. A 90 degrees elbow 21 is connected to hybrid 7 and a similar elbow (not shown) is connected to hybrid 7<SP>1</SP>. With one direction of magnetization, waves through guide 3 from left to right are retarded in phase by 90 degrees, and those from right to left are advanced in phase by 90 degrees, whilst a reversal of magnetization produces an opposite effect. A wave entering guide 5 through hybrid 7 from guide 17 is advanced in phase by 90 degrees, and a wave entering guide 3 through hybrid 7<SP>1</SP> from guide 5 is equally advanced so that the waves arrive at the output 180 degrees out of phase and cancel. However the effect of the ferrites and the compensator is to provide an additional 180 degrees relative phase shift between the two halves of the waves and they thus reinforce at the upper output arm of hybrid 7<SP>1</SP> which is arm B of the circulator. Similarly an input wave from arm B, dividing in hybrid 7<SP>1</SP> is so advanced that the two halves reinforce in waveguide 21 which is arm C of the circulator, and an input waveform arm C cancels in arm B and reinforces in arm D, whilst a wave from arm D cancels in arm C and reinforces in arm A. A reversal of polarization of the ferrites 9 reverses the direction of circulation, and if any arm is provided with a reflecting termination it will appear as a source of waves to the succeeding arm, and the device serves as a three-arm circulator. II Duplexer-switch. In a duplexer arrangement switching a transmitter and a receiver to two antennas directed in different directions a known pulsed transmitter 25 Fig. 3 (not shown) is connected to arm A of circulator 1, one antenna 29 is connected to arm B and a second antenna 30 to arm D, whilst the receiver is connected to arm C through an attenuator as described in Specification 817,585, the principle of operation being also described therein. In a further embodiment two transmitters alternatively use one antenna 29<SP>1</SP> Fig. 5 (not shown) a single section 41 serving as a monitor, the reversal of the circulator 1<SP>1</SP> connecting transmitters I and II. A further embodiment Fig. 6 employs two transmitters and two receivers feeding a common antenna and a monitor, the connections being made through two three arm circulators 431 and 43 2  and a four arm reversible circulator 1<SP>11</SP>. III Circulator Fig. 7. A different type of circulator utilizes the rotation of the phase of polarization of the wave propagated through it. In the embodiment described a length 51 Fig. 7 of circular waveguide has a ferrite pencil. 53 axially supported by polystyrene foam 55, flanges 57, 57<SP>1</SP> receiving the input and output rectangular waveguides 59 and 61 which are respectively oriented at 45 degrees to each other. Connected at right angles through the wall of guide 51 are waveguides 63 and 65 their long dimensions being parallel to the axis ' of guide 51. A polarizing winding 67 surrounds the ferrite element 53 which rotates the plane of polarization of waves propagated through guide 51 by 45 degrees, the direction of rotation depending upon the polarization of winding 67. Thus an input wave from guide 59 (arm A) is crosspolarized with respect to guide 63 and is not propagated through it, but is rotated by 45 and is propagated through guide 61 (arm B). A wave from arm B is propagated by guide 63 (arm C), and similarly the guide 65 acts as arm D. A reversal of current through winding 67 reverses the direction of circulation.