Patent GB-1108880-A (GB)
Title: Improvements in or relating to airborne triggering systems
IPC: G01S13/10
Filed: 1965-12-15
Abstract: 1,108,880. Pulse doppler radars. COMPAGNIE FRANCAISE THOMSON-HOUSTON HOTCHKISS BRANDT. 15 Dec., 1965 [17 Dec., 1964], No. 53310/65. Heading H4D. The invention relates to a radar device for detonating a missile charge M, Fig. 1, when it is within the radial range <SP>r</SP> min to <SP>r</SP> max of a target 0 and within an angular sector L<SP>1</SP> to L<SP>11</SP> extending α either side of the line Lo perpendicular to the missile's path P and passing through the target 0. The range limitation of the area of detonation is ensured by feeding the echo pulses, Fig. 7(c), (d), (e), through a range gate, Fig. 7(b) having a width equal to the echo pulses and a range equivalent width of <SP>1</SP>/ 3  (<SP>r</SP> max-<SP>r</SP> min), and centred on the range The variation of the output of the gate with varying range is thus as shown in Fig. 7(f). The angular limitation of the area of detonation is partly set by the antenna of the missile being arranged in array form around the circumference of the missile, such that the lobe of the antenna R<SP>1</SP>-R<SP>11</SP> has a fan configuration extending in a plane perpendicular to the missile axis and of angular thickness 2α, Fig. 3 (not shown). Its angular extent in said perpendicular plane is also limited, Fig. 2 (not shown). In order that an echo passing through the gate but not arriving from the immediately preceding transmitted pulse (i.e. the range being r 0  + a multiple of the repetition period #r range), the transmitted pulse train, Fig. 6 (not shown), is coded in phase in a random manner, each coding cycle being repeated over a large e.g. 1500 number of repetition periods. Thus each echo can be uniquely associated with its producing transmitted pulse. In Fig. 9, the output of the carrier source 810, (fo = 15Gc/s.) is gated at 812, by the output of pulse generator 1 to produce pulses of repetition period #r and width #, where # = #r/5. The pulses are fed to two gates 814a and 814b, a 180 degrees phase shift being introduced at the input of gate 814b. The required phase change code is set up in coder 803, and this causes a pulse generator 2 to open the appropriate one of gates 814a or 814b to let through a pulse with no phase change or with 180 degrees phase change according to the code. The pulse train (Fig. 6) is thus produced for transmission, the heavy outline of each pulse denoting its relative phase. The range gate pulse 21 is positioned half way through the repetition period by means of a delay 72 (delay = k.#r) inserted between the output of generator 1 and the control input of echo range gate 71. The gated echoes are coherently detected in mixer 819 by means of an output from generator 810. The resulting video after reshaping by further gating at 73 comprise pulses having absolute amplitudes varying according to the doppler signal, but with signs depending on the phase of the corresponding transmitted pulse. The code output of generator 2 is delayed by k.#r at 97 and used to produce a decoding signal which is applied to one input of a multiplying bipolar correlator 99 having the video applied to its other input. If each echo is due to the immediately preceding transmitted pulse the product output of correlator 99 comprises pulses all of one polarity as shown in (Fig. 8). This output is fed to a low pass doppler filter 93 having a cut off frequency such that only the signal within the period T r  and corresponding to the missiles passage through the angular area L<SP>1</SP>-L<SP>11</SP> is passed on to an integrating detector 94. When the doppler frequency is zero the missile is on line Lo nearest to the target, and the output of detector rises above the threshold of means 95 and actuates a firing circuit 96. Instead of detonating a missile the invention may be used to actuate a fly-by camera.