Patent GB-1195599-A (GB)
Title: Microwave Polarization Switch
IPC: H01P1/165
Filed: 1968-04-11
Abstract: 1,195,599. Waveguides. WESTINGHOUSE ELECTRIC CORP. 11 April, 1968 [17 May, 1967], No. 17569/68. Heading H1W. A high-speed arrangement for adjusting the polarization of a microwave signal-of use with radar-includes a first device for dividing microwave energy into two signals; a waveguide having first and second channels which are arranged to receive each a respective one of the two signals, and which contain means to shift the phase of each of the two signals by predetermined amounts ; a device for transferring, with a phase shift, both a portion of the energy associated with the first signal to the second signal, and a portion of the energy associated with the second signal to the first signal; and a device for finally receiving the two signals and converting them to circularly polarized signals, whereby, if the phase shifts are so arranged that one or other of the two signals entering the polarizer is zero, either left or right circularly polarized waves are provided, while otherwise waves plane polarized at a desired angle are provided by interference between the two signals. As shown, the two signals derived by the folded "magic-T" from a linearly polarized signal introduced at the flange 14 are fed into passages 38 and 40 of the phase shifter 30. The latter is constituted by the partitioned waveguide 36, each passage of which contains annular ferrite segments-e.g. 46 and 48 in the channel 40-separated and terminated by annular, non-magnetic; dielectric spacers 42, longitudinal conductors-e.g. 50-passing through the segments and spacers to permit the production of desired orientations of magnetization of the ferrite segments by the application of current pulses to connections 52, 54, 56. The signals from the phase shifter 30 are fed, via a 90 degree hybrid coupler 70 formed by a waveguide 76 having a central slotted partition 78, to a polarizer constituted by a waveguide 96 having a central tapered fin 98. The polarizer converts a linearly polarized signal entering channel 102 or 104 into a right or left circularly polarized signal respectively at the further end flange 94, while right or left circularly polarized signals entering flange 94 are converted into linearly polarized signals issuing from channels 102 and 104 respectively. In one mode of use, in a radar system, the ferrite segments in the phase shifter are arranged, Fig. 7, to provide a 90 degree phase shift for either left or right-going signals in channel 40, while in channel 38 left-going signals are unaffected while right-going signals suffer a phase shift of 180 degrees. In transmission, Fig. 7a, a linearly polarized signal is, as shown, converted in the phase-shifter and hybrid coupler into a single signal entering channel 104 of the polarizer, and hence into a leftcircularly polarized signal at the polarizer. output. The right-circularly polarized reflected signal is, conversely, converted, Fig. 7b, into a linearly polarized signal in channel 102, and subsequently by the hybrid coupler and phase shifter into a pair of equal phase linearly polarized signals for entry into the "magic T". In further modes of operation, the phase shifts produced in the two channels of the phase shifter are arranged such that signals enter both channels of the polarizer, the resultant left and right circularly polarized signals produced by the polarizer interfering to provide at the output either a vertically (Fig. 9, not shown) or a horizontally (Fig. 10, not shown) polarized transmission signal. In modified apparatus, the ferrite segments may be chosen to provide less than a 90 degree phase shift, whereby an elliptically polarized signal may be produced ; or a sequence of segments may be employed capable of effecting a phase shift of progressively smaller magnitude e.g. 90, 45, 22À5 and 11À25 degrees (Figs. 11 and 12, not shown), whereby the system is capable of rotating the plane of polarization from - 90 to + 90 degrees in 2<SP>n</SP> steps of α degrees per step, where n is the number of ferrite segments and α is half the phase shift produced by the smallest segment.