GB811470A - Improvements in or relating to pulse radar apparatus - Google Patents

Abstract

811,470. Pulse radar. DECCA RECORD CO. Ltd. June 26, 1957 [July 2, 1956], No. 20496/56. Drawings to Specification. Class 40(7). In a pulsed radar system use is made of multiple returns for detecting targets at long range. In such an apparatus the interval between successive transmitted pulses is systematically altered from one to another of two different values which differ by an amount greater than the duration of the transmitted pulse but small compared with the duration of the intervals. In the general case of n returns the transmitter is arranged to give pulses at n short intervals followed by n long intervals. If the display time bases are triggered to start at the same time as the transmitted pulses the first return echoes will paint as a single response on the display, the second will paint as two responses and the nth will paint as n responses. Second and subsequent returns may be identified by counting the number of responses on the screen for the particular target in question. In such an arrangement the ground, or first, return would tend to obscure the normally less-bright multiple responses on the display. Removal of the first returns can be effected by passing the echoes through a delay line such that the first return from one pulse cancels with the first return from the subsequent pulse. As the interval between pulses is not constant it is necessary to provide two delay lines, one with a delay equal to the shorter interval and the other with a delay equal to the difference of the two intervals, controlled by an electronic switch such that the lines may be used separately or in series to provide the appropriate delay for cancellation of first returns. The delay lines may also be used to determine the timing intervals between the transmitter pulses by passing a trigger pulse from the delay line through a regenerator back to the delay line input so that the pulse is recirculated with the appropriate time intervals and any variation in delay is automatically applied both to the transmitter pulse intervals and to the video intervals. When it is desired to identify one particular return the timebase sequence may be started at a pulse other than the starting pulse of the transmitter sequence. By this means any particular return may be made to paint as one response, other returns painting as multiple responses. First return responses may still be cancelled as explained above. For measuring the range of targets appearing as second and higher returns a conventional type of calibrator or stroke circuit may be used.