Patent GB-1411991-A (GB)
Title: Adjustable polarization system
IPC: H04B7/10
Filed: 1972-09-22
Abstract: 1411991 Phase changers RCA CORPORATION 26 Jan 1973 [22 Sept 1972] 44050/72 Heading H1W [Also in Division H4] An apparatus for rotating the plane of polarization of linearly polarized waves comprises an adjustable power divider which produces two linearly polarized outputs from a linearly polarized input. These outputs are combined in coupling means, with the plane of polarization of one rotated by 90 degrees relative to the other. The direction of the plane of polarization of the resultant output is dependent upon the relative magnitudes of the two outputs from the power divider, and may be altered as required by adjustment thereof. As described, a dualfrequency, dual-polarization radio station, Fig. 3, comprises transmitters T x1 , T x2  operating on a frequency F1, and a feed horn 45 with an associated reflector from which are emitted waves which are linearly polarized in respective orthogonally disposed planes. The station also comprises receivers R x1 , R x2  operating on a frequency F2, and it receives therefrom waves which are linearly polarized in respective orthogonally disposed planes. Each pair of planes may be independently rotated, by adjustment of power dividers 11, 13, and this feature is of particular utility when working to an earth satellite station, to counter the effects of ionospheric Faraday effect rotations. The station may be adapted to operate with circularly polarized waves by fitting a polarization converter 71 to said horn 45. The power divider 11  comprises four short slot hybrids 15, 17, 19, 21 with an adjustable plunger system 23, and the power divider 13 is similar. In each hybrid an input at one port provides outputs of equal powers but with 90 degrees relative phase difference at the two opposite ports. The adjustable double plunger system 23 is shown in more detail in Fig. 4, the system 69 of the divider 13 being similar. It comprises two side-by-side waveguide sections 25, 26 containing plungers 25a, 26a which are slidable together. The ends 25b, 25c and 26b, 26c provides reflective shortcircuits for waves launched in the waveguides choke grooves 31 being so disposed along the plungers as to improve the short-circuiting effect. Considering the transmitter T x1 , signals applied at terminal 16 are equally power divided by the hybrid 15, with the signals at the port 15b being phase shifted 90 degrees relative to those at the port 15a. The signals from the port 15a are coupled to the hybrid 17 at the port 17a and are equally power divided with the signals at port 17c being phase shifted 90 degrees relative to those at the port 17b. Signals from the ports 17b, 17c are then coupled to the adjustable double plunger system 23 at its end 23a, and are reflected back with an equal phase shift into the hybrid 17, where they are recombined in phase so that the total signal applied to said hybrid is coupled out of its port 17d to port 21a of the hybrid 21. Similarly the 90 degree phase shifted signal from the transmitter T x1  at the terminal 15b of the hybrid 15 is coupled via the hybrid 19 and the end 23b of the adjustable plunger system 23 to port 21b of the hybrid 21. The effect of the system 23 is to impose inverse phase shifts (e.g. + #‹ and -#‹) upon the said signals which are additional to the 90 degrees relative phase shift due to the hybrid 15. The consequent outputs at the ports 21c, 21d of the hybrid 21 are in phase, with relative magnitudes determined by #. When the plungers 25a, 26a are in their centred position, so that the relative phase between the signals coupled to the ports 21a, 21b is 90 degrees, all the power is coupled out of the port 21d. If the movement of the plungers 25a, 26a is such that an additional phase change of 180 degrees is introduced, all the power is coupled out of the port 21c. The ratio of the powers coupled out of the ports 21c, 21d may be varied between these extremes by suitable movement of the plungers 25a, 26a. The two signals from the ports 21c, 21d are coupled through duplexers 35, 41 to respective input ports 38, 40 of an orthogonal coupler 39, the plane of polarization of the signal from the port 21d being rotated by 90 degrees relative to the signal from the port 21c by means of a rotator 37. The coupler 39 effects a vector summation of the in-phase orthogonally polarized signals, to produce a resultant signal whose plane of polarization is angularly displaced from that of either of its constituents by an amount which is determined by the ratio of their magnitudes. Signals from the transmitter T x2  at terminal 18 are applied to the other input port of the hybrid 15, and result in output waves from the coupler 39 which are linearly polarized in a plane perpendicular to that of the waves from the transmitter T x1 . Operation of the double plunger system 23 rotates both planes together, their orthogonal relationship being maintained. Received linearly polarized signals of frequency F2 in two orthogonal planes are separated out in the duplexers 35, 41 and are coupled through the power divider 13 to respective terminals 16a, 18a. The orientations of their orthogonally disposed planes of polarization may be adjusted by operation of the double plunger device 69, independently of the orientations of the planes of polarization of the transmitted signals.