Patent GB-1245245-A (GB)
Title: Improvements in or relating to proximity fuzes for missiles
Inventor: GOWLER EDMOND JOHN
IPC: G01V3/10
Filed: 1967-10-11
Abstract: 1,245,245. Proximity fuzes. EMI Ltd. 20 Sept., 1968 [11 Oct., 1967], No. 46502/67. Heading F3A. [Also in Division H4] A proximity fuze for a missile comprises an oscillator/transmitter part shown to the left of the dashed line in Fig. 1 and a trigger part shown to the right of the line, these two parts being received, respectively, in compartments 61, 62 in the missile nose. The oscillator/transmitter part includes a transistor 1 operating as a Colpitts oscillator, the oscillator output being connected through a tuning coil 11 to the missile nose, the missile body acting as a halfwave dipole. The emitter is connected to a - 8V line 5 via a coil 13 and resistor 31. The transistor 1 is biased by a potentiometer comprising a resistor 32 and diodes 51, 52 connected between the line 5 and a 6V supply line 4, the collector being connected to the line 4 via a resistor 33. In operation, the load on the oscillator changes in the presence of a target and this change alters the current taken by the oscillator from the supply line 4. The resultant change in voltage generated across the resistor 33 is used to operate the trigger and explode the missile. The trigger part includes complementary transistors 2, 3 connected in a D.C. positive feedback loop. The transistors are normally non-conducting but a change in voltage across resistor 33 of about 1À5V which is applied to the base of transistor 2 renders both transistors 2, 3 conducting and produces a negative trigger step of 11V at the collector of transistor 3. The firing level of the trigger is determined by diodes 54, 55 and resistors 37-39. The trigger output is supplied to a line 6, the trigger voltage being multiplied in a circuit (Figs. 5, 6, not shown) so that a voltage pulse of about 45V with an energy of 40 microjoules is applied to the ignitor. Fig. 3 shows the form of the voltage appearing at the collector of transistor 1 when the missile approaches a target in such a way that its longitudinal axis is parallel to the target plane. This represents the situation in practice when the missile would pass the target without hitting it. The ordinate represents voltage and the abcissa represents the ratio between distance, d, from the target and the wavelength, X, of the oscillation transmitted from the oscillator, and it is also calibrated in distance in metres for the oscillator frequency used, viz. 80 MHz. As a target is approached the effective load on the oscillator fluctuates when the target is close enough producing a number of negative peaks until at very close approach, when d is less than half a wavelength, the voltage decreases considerably. It is this last decrease which is detected by the trigger circuit and used to fire the missile. Thus if the trigger threshold is set at a value below approximately 11À6V the fuze will not fire on the negative peak at just over 2 metres, but will fire when the target is closer than approximately 0À6 metres as desired. The curve shown in Fig. 4 shows a curve similar to that shown in Fig. 3 but representing the situation when the missile approaches a target in such a way that the longitudinal axis is perpendicular to the target plane and the missile would hit the target. In this case it will be seen that with the threshold set below 11À6V as described above the trigger will never fire because on close approach to the target the oscillator voltage after several fluctuations goes more positive instead of going more negative as described above. The fuze described thus discriminates between near miss conditions, when it will fire, and direct hit conditions when it does not fire. If it is also desired to use the fuze to detonate the missile in direct hit conditions, then a second trigger circuit can be provided which responds to a positive change in the oscillator voltage.