GB1282727A - Improvements to electromagnetic detection and triggering systems - Google Patents

Abstract

1282727 Proximity fuse THOMSON-CSF 23 Dec 1969 [27 Dec 1968] 62699/69 Heading H4D A radar carried on a moving object has a random or pseudo-random code generator feeding a modulator which modulates a C.W. signal by phase reversal according to the code, to provide transmission signals wherein the code is also fed through a delay to a correlator which also receives the video signals from a CFAR, the output of the correlator feeding a Doppler filter, a detector and a matched integrator which feeds a triggering circuit and wherein the receiving and transmitting aerials are separate and each have radiation patterns defined by two cones coaxial with the moving object. In a proximity fuse for a guided missile, a shift register 32 and feedback element 33 produce a pseudo-random binary code which is fed to one input of a modulator 2. The signal input from klystron 1, through isolator 19 is of a frequency higher than "normal" radar transmissions. The output of the modulator 2 is a C.W. signal whose phase corresponds to the code (Fig. 3, not shown). This signal is transmitted by aerial array 41, 42. Reflected signals are received by a second array 51, 52 and pass through a magic-T junction 60 which feeds a symmetrical mixer 61, 62. The second input to the magic-T being a portion of the unmodulated transmitted signal. The outputs from the mixers 61, 62 supply amplifiers 91, 92, amplifier 92 including thresnold circuits which are arranged to provide a constant false alarm rate. The output from the receiver will thus be a binary code, amplitude modulated by a Doppler frequency dependent on the velocity of the target. The received signals are compared in a correlator 10 with the modulating code delayed by an amount corresponding to a range within the missile detonation limits (R 1 , R 2 Fig. 1, not shown). Thus when the target is at this range, the correlation function is unity and the video signals pass to a bank of Doppler filters 122j, each covering a selected velocity range and each having a matched integrator 132j. These feed a threshold circuit 141 which actuates a trigger 142 to detonate the missile when a threshold S is exceeded. The aerials 41, 42 and 51, 52 may be arrays of linear elements or may be of a circular geometry and are arranged to have radiation patterns defined by two cones coaxial with the missile (Fig. 1, not shown). The pattern produces a narrow beam of 5 to 10 degrees. Thus the video signals must satisfy rigid conditions of angular position (due to aerial patterns), range (due to correlation) and velocity (due to Doppler filters) in order to detonate the missile. This ensures that the missile is unlikely to be detonated by interference or E.C.M. Also the use of a high radar frequency enables a low power to be used i.e. discrete transmission.