GB750600A - Improvements in or relating to radar systems - Google Patents

Abstract

750,600. Radar. MINISTER OF SUPPLY. May 11, 1953 [May 26, 1952], No. 13330/52. Class 40 (7). A radar apparatus using circularly polarized radiation comprises an antenna structure including a converter for changing circularly polarized received radiations into horizontally and vertically polarized components, a pair of channels each adapted to receive one of the components, and utilization means for comparing or combining signals from the channels additively, subtractively, and with or without phase discrimination to provide in a display an indication representative of selected components of the incident signals. In the system shown in Fig. 3 a transmitter 1 feeds an antenna 2 through a common T and R device 3 and a circularizer 4 which transforms plane polarized waves into circularly polarized waves. Received circularly polarized waves are converted by the circularizer 4 into vertically or horizontally polarized waves according to whether they are left-hand or right-hand circularly polarized; the vertically polarized waves are fed through channel a to a mixer 6a and amplifier and detector 10a, and the horizontally polarized waves are fed through channel b to similar units 6b, 10b. The detected signals are fed to a signal comparison unit 11 which comprises circuits for adding or subtracting the signals from the two channels and passing an output to the display circuit 12. The mixers 6a and 6b are fed by a common local oscillator 7, and the outputs from the mixers are also fed to phase sensitive amplifier 8 and display circuit 9. Channel b is provided with a phase control 5 which enables the relative phases of the two channels to be adjusted. In operation if the outputs from channels a and b are added, the system operates like a normal plane-polarized system; if they are subtracted, any contaminating phase polarized signals are eliminated at the cost of a reduction in the signal strength of the wanted target signals. If the output is taken only from channel b reflections from symmetrical objects, e.g. raindrops, are eliminated; if the objects are not perfectly symmetrical their echos may be reduced by feeding in the appropriate phase a controlled amount of signal from channel a into channel b before detection, the phase being adjusted by the control 5. The phase sensitive amplifier 8 and display 9 may be used in conjunction with the phase control 5 to determine the plane of polarization of received signals and may be used in this way for target identification. Fig. 4 shows one form of antenna system where the transmitter feeds a rectangular waveguide 21 with vertically polarized radiation, and the waveguide 21 is connected to a receiver through a TR switch 23 and to a square waveguide 24 which is connected to another receiver, through a phase control 27 and TR switch 28, and. to a section 29 which converts transverse excitation to diagonal excitation; this section 29 feeds a circularizing section 30 and a horn 31. Received radiation is transformed by sections 30 and 29 into horizontal and vertical components in the waveguide 24, which is provided with a grid 25 which reflects the horizontal components into the plane control 27 and TR switch 28 but allows the vertical components to pass to the TR switch.