GB906502A - Improvements in or relating to pulsed radar systems - Google Patents

Abstract

906,502. Pulse radar. MARCONI'S WIRELESS TELEGRAPH CO. Ltd. May 28, 1959 [Sept. 25, 1958], No. 30734/58. Class 40 (7). A radar system comprises a pulse transmitter, a frequency selective radio receiver, means for rapidly sweeping the selection frequency of the receiver through a frequency range including the transmitter frequency so that each received echo pulse causes the receiver to produce a series of output pulses at a P.R.F. determined by the sweep frequency, and means for using the output pulses for target indication. The aim of the system is to resist carcinotron jamming. In the system shown a master oscillator 1 controls a transmitter 4 which transmits 10 Ásec. pulses. Received pulses are mixed at 7 with the output of a local oscillator whose frequency is swept at 5 mc./sec. The mixer output is fed through an amplitude limiter to a gate 13 which is open for 25 mÁec. only at moments when the swept frequency is such as to combine with the transmitter frequency to produce a predetermined intermediate frequency. The amplitude limiter limits amplitudes to the value of the strongest echo signal expected, and the limit may fall from a high value after a pulse to a low value just before the next pulse. The output from the gate is fed to five parallel gates such as 15, 25, which open in succession for 1 Ásec. each under the control of multivibrators such as 17, 27. Each of these gates is followed by a chain of counters 18, and the outputs of the counters are fed in parallel to a coincidence detector 20 which provides an output pulse for target indication only if all five chains of counters have counted the same, predetermined number of pulses-in the present case, ten, since the local oscillator frequency has the correct value to produce the predetermined I.F. ten times in one Ásec. The counters are reset after every five Ásec. Means may be provided for producing a display only when successive echos occur at the same range. The transmitter and sweep frequencies may be variable.