Patent GB-932808-A (GB)
Title: Improvements in or relating to electric signal combining arrangements
Inventor: EASTER BRIAN
IPC: H04B7/08
Filed: 1960-09-30
Abstract: 932,808. Radio receiving systems; automatic phase control systems. GENERAL ELECTRIC CO. Ltd. July 3, 1961 [Sept. 30, 1960], No. 33694/60. Class 40 (5). In a radio diversity receiving system the signals from two antennµ are combined through a phase shifter so that two further equal signals are obtained (e.g. the vector sum and difference of the input signals), the further signals are then combined through a phase shifter so that the total antennµ input energy is applied to a receiver, and both phase shifters are automatically adjusted by retroactive control systems for any change in relative amplitude and/or phase of the antennµ input signals. In Fig. 1 two rectangular waveguide input channels from antennµ 1, 2 are connected in phase quadrature to the non-collinear arms of a magic-T 12 through adjustable phase shifter 15 and both channels phase modulated differentially in modulators 6, 8 by a low frequency f 1  applied to ferrite modulators. The outputs, therefore, amplitude modulated at frequency f 1  about equal mean signal levels, are then further phasemodulated differentially at low frequency f 2  and connected in phase opposition through adjustable phase shifter 26 with the collinear arms of a further magic-T 23 so that all energy is directed to a receiver 4, and the amplitude modulation at f 1 , f 2  is detected by an amplifier and amplitude demodulator 31. The outputs f 1 , f 2  are then compared with modulator sources f 1 , f 2  in phase sensitive rectifiers 38, 44 giving outputs in sign and magnitude determined by phase errors, if any, between the two inputs to magic-T's 12, 23, respectively, and adjust through motors 41, 47 the phase shifters 15, 26 so that the required phase difference of the two inputs to magic-T's 12, 23 is obtained. In an modification (Fig. 2) the two plane polarized channels, oppositely phased modulated at f 1 , are connected to ports 51, 52 of a circular waveguide to produce elliptical polarization and rotated by an adjustable #/2 dielectric plate phase shifter 55, so that the two plane polarized components parallel to the inputs at 51, 50 are made equal, and differentially phase modulated at 58, before being applied to a #/4 dielectric phase shifter plate 60 inclined at 45 degrees to the two directions of polarization, so that each is converted to circular polarization in opposite directions, i.e. combined they form a plane polarized wave whose polarization varies with the phase difference between the two circularly polarized waves. This phase difference is adjustable by a #/2 dielectric plate phase shifter 61 so that the equivalent plane polarized wave is adjusted in polarization so'that all the energy is directed to either output port 52 or 53 connected to the receiver. The two phase-shifters 55, 61 are then each controlled by automatic phase control as in Fig. 1. Alternatively both phase modulations may be produced by oscillating the phase shifter plates 55, 61 through a small angle, and in phase quadrature if the oscillation frequency is the same. In Fig. 4 the two antennµ are connected by rectangular waveguide to ports 101, 102 at rightangles in a circular waveguide. The latter comprises two Faraday polarization rotating modulators 69, 70 each comprising ferrite cores 106 and energized by phase quadrature inputs of a single modulating low frequency f 1 , and two rotatable phase shifters 71, 72, respectively a #/4 and a #/2 dielectric (quartz) plate. Plate 110 is automatically adjusted so that it is always in line with the major axis of the resulting elliptical polarization and hence produces two equal circularly polarized waves of opposite directions of polarization, i.e. a plane polarized wave whose polarization varies with the phase difference between the circularly polarized waves. Plate 112 is adjustable so that this plane polarized wave is rotated to a position directing all output energy to port 103 or 104 connected to a receiver and to an amplitude demodulator detecting the two phase quadrature components of f 1 . The latter is compared in phase-sensitive rectifiers with corresponding phase quadrature components of the modulating source f 1  to derive two outputs, if any, adjusting the phase shifters 71, 72. The two outputs may act (Fig. 3, not shown) on reactances varying the phase of two oscillators of frequency f 2  each having two outputs in phase quadrature and compared with a reference oscillator of equal frequency f 2  in phase discriminators. The two pairs of phase discriminators produce outputs cos #, sin #, cos #, sin # where #, # depend on the phase across, if any, of phase shifters 71, 72, and are applied to pairs of windings controlling the magnetic field direction applied to the #/4 and #/2 dielectric plates. The latter may have magnetic edge parts as described in Specification 933,809, to rotate them into alignment with the magnetic field. The control for the first phase shifters may be arranged to be quicker acting than that for the second phase shifters. To allow for ambiguity in the systems, the output magic-T hybrid may have connected to its conjugate output arm a further stand-by receiver. The signal energies of three or more antennµ may be combined without loss by two or more of the above systems.