JP3540776B2 - Passive Doppler fuze - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to electronic circuits and systems, and more particularly to electronic fuses used in weapon systems.
[0002]
[Prior art]
In many applications, there is a need to provide a military fuze. Some applications require inexpensive, passive proximity fuses. For example, the Global Positioning System (GPS) is currently used to provide accurate weapon guidance to targets by satellite constellation. It is anticipated that the use of multiple inexpensive GPS transmitters will be deployed as a countermeasure to disrupt the GPS guidance system of missiles or other weapons in flight.
[0003]
There is a need for weapons that can track automatically and destroy GPS jammers. Jamming transmitters are small, elevated and difficult to break. Therefore, inexpensive missiles are currently being considered for this application. Missiles travel at high speeds and therefore typically require both a guidance system and a fuze. The guidance system guides the weapon to the target and attempts to collide with it, and the RF fuze must strike the target and detonate the weapon if the fuze fails to operate. This significantly increases the cost of weapons as radar transmitters, receivers, and signal processors are typically required. With respect to passive fuze methods, known RF fuzes are unsatisfactory, and active fuzes are expensive because a radar transmitter system or other active detection method is required.
[0004]
[Problems to be solved by the invention]
Unfortunately, it is expected that many inexpensive jammers will be deployed as jammers. Therefore, these methods are impractical because of the high cost associated with the aforementioned active fuze and accurate guidance system methods for jammer opposition weapons. Furthermore, the guidance system and the active fuze method also have a negative effect on the form factor of the solution.
[0005]
There is a need in the art for an inexpensive alternative means to allow the use of inexpensive weapons to destroy small and inexpensive jamming source targets.
[0006]
[Means for Solving the Problems]
The need for this technique is addressed by the passive proximity fuse of the present invention. The fuze of the present invention is configured to be mounted on a weapon and includes a receiver configured to be locked to a signal transmitted by a jamming transmitter. The receiver detects a Doppler shift in the signal as the weapon approaches the target. When the point of closest approach is reached, the Doppler shift changes from increasing to decreasing. The fuse of the present invention includes a mechanism for detecting a change in the Doppler shift, and outputs an explosion signal in response thereto. That is, the passive fuse of the present invention is connected to the receiver for detecting a signal radiated from the signal source, detects a Doppler shift in the detected signal, and outputs a Doppler signal in response thereto. It comprises a first circuit and a second circuit that calculates a second derivative of the Doppler signal and generates an output signal responsive thereto.
[0007]
In the illustrated embodiment, the receiver is an FM receiver. The mechanism for detecting a change in Doppler shift may be constituted by a discrete analog circuit or digital circuit. In the illustrated analog structure, first and second resistor / capacitor (RC) networks are used to calculate the second derivative of the Doppler shifted signal output by the receiver. This signal is then amplified and compared to a threshold to provide an output detonation signal.
[0008]
In the digital structure shown, the output of the receiver is converted to a digital signal, which is processed by a digital signal processor (DSP). The DSP calculates the second derivative of the Doppler shifted signal output by the receiver in response to a stored program for calculating the second derivative. The output of the DSP is an explosion signal. Thus, the explosion is realized by cheap passive means at the point of closest proximity of the weapon to the target.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
The illustrated embodiments and exemplary applications are described with reference to the accompanying drawings to disclose the advantages of the present invention.
While the invention will be described with reference to illustrative embodiments of particular applications, it should be understood that the invention is not limited thereto. Those skilled in the art will recognize additional modifications and application embodiments within the scope of the invention and in particular areas where the invention is very effective.
[0010]
FIG. 1 is an explanatory diagram of the operating environment of the proximity fuse of the present invention. The fuze 10 of the present invention is configured for use with a weapon 11 for destroying a jamming transmitter 12.
[0011]
FIG. 2 is a schematic diagram of an exemplary analog structure of the fuse of the present invention. Fuze 10 includes an antenna 14 that receives the signal transmitted by jamming transmitter 12 of FIG. 1 and provides it to receiver 16. In the preferred embodiment, receiver 16 is configured to receive a frequency modulated (FM) signal and provide an output in response. Preferably, receiver 16 is tunable to allow use for jammers operating at various carrier frequencies. Receiver 16 outputs a signal indicating the Doppler shift of the carrier signal transmitted by jammer 12 as weapon 11 approaches. The Doppler shift phenomenon is well known in the art. When a periodic signal is transmitted between a source and a receiver that move relative to each other, a shift in the periodicity of the received signal is detected. This shift is known as a Doppler shift, and the associated Doppler frequency f _d is given by:
_{f d = V · f t cosα} / c [1]
Where _ft is the frequency of the transmitter,
V = speed of weapon 11;
c = light speed,
α = the angle between the flight line and the transmitter 12 as shown in FIG.
[0012]
As a function of time, equation [1] may be expressed as:
_{f d (t) = V ·} f t Vt / c · (V 2 t 2 + m 2) 1/2 [2]
Here, “m” is a miss distance.
[0013]
The purpose is to explode 11 or ignite the fuze at the point of closest approach to the jamming transmitter 12. In accordance with the present invention, the point of closest approach is detected by taking the second derivative of f _d (t) and detecting its inflection point (ie, when the second derivative crosses zero). This is shown in FIGS. 3A-C as described more fully below.
[0014]
FIG. 3A illustrates the Doppler shift f _d (t) of the received signal as a function of time.
[0015]
FIG. 3B shows the first derivative of the Doppler shift f _d (t) of the received signal as a function of time.
[0016]
FIG. 3C shows the second derivative of the Doppler shift f _d (t) of the received signal as a function of time. In FIG. 3A-C, the point of closest approach is at t = 0.
[0017]
Returning to FIG. 2, in the analog structure, the point of closest approach is detected by two RC networks: R ₁ C ₁ , R ₂ C ₂ and a comparator. As will be appreciated by those skilled in the art, the RC network is connected as a high pass filter for differentiating the Doppler signal output by the receiver 16. The first RC network R ₁ C ₁ provides the first derivative of the Doppler signal output by the receiver 16 and the second RC network R ₂ C ₂ provides the second derivative of the Doppler signal output by the receiver 16. Output a function. Amplifier 18 is located between the first and second RC stages to separate the two networks.
[0018]
The comparator 20 compares the output of the _second differentiator R ₂ C ₂ with a threshold set by a voltage dividing network consisting of resistors R ₃ and R ₄ connected to a reference terminal. Voltage division basically determines the distance at which the fuse detonates.
[0019]
FIG. 4 is a diagram showing the output of the fuse comparison device of the present invention. As shown in FIG. 4, the output of the comparator when the second derivative of the Doppler shift crosses the threshold voltage V _T of the comparator will be low at t _1, the second derivative of the Doppler shift higher in the second time t ₂ when it crosses the threshold voltage V _T.
[0020]
FIG. 5 is a diagram showing the output of the fuse of the present invention. As shown in Figure 5, weapons t ₂ is triggered to explode in the point of closest approach t = 0.
[0021]
Returning to FIG. 2, the output of the comparator 20 is connected to an analog-to-digital (or analog TTL) converter 22 to provide a digital output pulse, if necessary.
[0022]
FIG. 6 shows another digital structure of the fuse of the present invention. In a digital configuration, the fuze 10 'includes an analog-to-digital converter 24 that digitizes the output of the receiver 16 and provides a digital Doppler shift to a digital signal processor (DSP) 26. As will be appreciated by those skilled in the art, the DSP may be provided with a microprocessor or programmable logic gates. In a microprocessor structure, the DSP operates software (indicated at 28) to continuously calculate the second derivative of the Doppler shift of the signal and provides an output signal in response.
[0023]
Those skilled in the art will recognize that the present invention is not limited to the structure shown, and that the passive Doppler fuze of the present invention operates independently of the absolute frequency of the transmitted signal.
[0024]
Accordingly, the present invention has been described herein with reference to a particular embodiment for a particular application. Those skilled in the art will recognize additional modifications, applications, and embodiments within the scope of the present invention.
[0025]
The invention can also be used to hit any transmitter. For example, the transmitter can be mounted on an airplane or ground vehicle where an auto-tracking guidance device is used to locate the target. The present invention is used to ignite an explosive load without the guidance system hitting the target with aerodynamic control.
[0026]
The present invention can also be used to attack any transmitter that appears to be a military target.
[0027]
It is therefore intended that any and all such applications, modifications, and embodiments within the scope of the invention be covered by the appended claims.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an operating environment of a fuse of the present invention.
FIG. 2 is a schematic diagram of an analog structure of a fuse of one embodiment of the present invention.
[3] The Doppler shift f _d of the signal received as a function of time _(t), and the first derivative of the Doppler shift f _{d (t),} and a second derivative of the Doppler shift f _{d (t)} FIG.
FIG. 4 is a diagram showing an output of the fuse comparison device of the present invention.
FIG. 5 is a diagram showing an output of a fuse of the present invention.
FIG. 6 is a schematic diagram of another digital structure of the fuse of the present invention.

Claims (7)

A receiver for detecting a signal emitted from the signal source;
A first circuit connected to the receiver for detecting a Doppler shift in the detected signal and outputting a Doppler signal in response thereto ;
Second passive fuse that includes a circuit for generating an output signal in response thereto by calculating the second derivative of said Doppler signal. It said second circuit includes a first resistor and a passive fuse of claim 1 and a capacitor network for generating a Doppler signal is differentiated by differentiating the Doppler signal. It said second circuit includes a second resistor and a passive fuse of claim 2 wherein is provided with a capacitor network for further differentiating the Doppler signal said differentiated. 4. The passive fuse of claim 3 further comprising an amplifier disposed between said first and second networks of resistors and capacitors . 4. The passive fuse of claim 3 further comprising means for comparing the output of the second resistor and capacitor network to a predetermined threshold. The second circuit is passive fuse of claim 1, characterized in that comprises a digital signal processor. 7. The passive fuse of claim 6, wherein the second circuit comprises software for operating the digital signal processor to calculate a second derivative of the Doppler signal and generate an output signal responsive thereto. .

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