GB1081971A - Improvements in and relating to radar apparatus - Google Patents

Abstract

1,081,971. Radar. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. May 6, 1957 [May 9, 1966], No. 14412/56. Heading H4D. To reduce the effect of a jamming signal on a radar receiver, the form of the jamming signal is determined, at the receiver, and the receiving circuit parameters are correspondingly adjusted, automatically, to reject the jamming signal. To prevent the simultaneous rejection of the target echo signal, the jamming rejection circuit is provided with a further control, the character of which depends on whether the radar is of the pulse or C.W. type. For a pulse system, the adjustment of the continuously adjustable jamming rejection circuit is discontinued by blanking signals from the receiver, during the time interval when the reflected pulse is expected. Thus, if the jamming signal changes slightly during this interval, only a small jamming signal will pass into the receiver. The required echo, on the other hand, passes freely into the receiver as the jamming rejector circuit is not now following changes in the antenna signals and is adjusted to reject only those existing on the antenna prior to the reception of the echo. For C.W. systems, the rejection circuit may be rendered insensitive to the required reflection frequency by the insertion of a band rejection filter tuned to the required echo frequency. The receiving aerial accepts, separately and simultaneously, two orthogonally polarized signals V and H and the adjustable phase shifters, I and II in the input channels A, B are adjusted by the automatic control signals from phase sensitive detectors I and II and effect the jamming signal rejection. The phase shifters may be reactance valves or goniometers.