WO2006020864A1

WO2006020864A1 - Jamming system

Info

Publication number: WO2006020864A1
Application number: PCT/US2005/028734
Authority: WO
Inventors: James Henly Cornwell
Original assignee: James Henly Cornwell
Priority date: 2004-08-12
Filing date: 2005-08-12
Publication date: 2006-02-23
Also published as: WO2006020864A9

Abstract

The system (10) includes a generator (20), a first device (30), a second device (40), and a third device (50) that are located at vertices of the area to be protected. The first device (30) has a receive antenna (32), a transmit antenna (34), an antenna unit (36) and a programmable feed unit (38) that is coupled between the antenna unit (36) and the generator (20). The second devise (40) and the third device (5) are configured similarly to the first device (30). The system (10) relates to the jamming of triggering devices that are used with improvised explosive devices.

Description

JAMMING SYSTEM

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to jamming systems. In particular, the invention relates to electronic countermeasure jamming systems that are capable of interrupting radio links from triggering devices used in connection with improvised explosive devices.

Description Of Related Art

Known countermeasure systems have diverse broadband radio signal generators that are fed into a relatively simple antenna. The antenna attempts to have omni¬ directional coverage. The simplest antenna is a half dipole oriented vertically at the center of the area to be protected by jamming. The problem with such antennas is that they do not have spherical coverage patterns for truly omni coverage. Coverage of such a simple antenna appears shaped like a donut with gaps in coverage above and below the plane of the donut because the simple dipole cannot operate as both an end fire antenna and an omni antenna. More complex antennas may add coverage in end fire directions but generate interference patterns that leave gaps in coverage. hi an environment where small improvised explosive devices (IED) are placed in airplanes, busses or trains and triggered by radio links distant from the IED, it becomes more important to successfully jam the radio link without gaps in jamming system coverage.

SUMMARY OF THE INVENTION

A jamming system includes a generator and at least three devices located at respective vertices of an area to be protected Each device includes a transmit antenna, a receive antenna, an antenna unit, and a programmable feed unit coupled between the antenna unit and the generator.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be described in detail in the following description of preferred embodiments with reference to the following figures.

FIG. 1 is a block diagram of a jamming system according to the present invention.

FIG. 2 is a block diagram of a device showing details of an antenna unit according to the present invention.

FIG. 3 is a plot illustrating the zone of coverage of a jamming system according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A first embodiment of the invention is depicted in FIG. 1, where a system 10 includes a generator 20 and at least three devices 30, 40 and 50 located at vertices of an area to be protected. A first device 30 includes a receive antenna 32, a transmit antenna 34, an antenna unit 36 and a programmable feed unit 38 coupled between antenna unit 36 and generator 20. A second device 40 is similarly configured, and a third device 50 is similarly configured. In each device, a signal received at the receive antenna is amplified and broadcasted from the transmit antenna so that the device itself oscillates and produces a random noise signal. In an alternative embodiment of the invention, the system further includes a fourth device also configured at a vertex of the area to be protected.

In a variant of the first embodiment and as depicted in FIG. 2, each antenna unit 36, 46 and 56 in each device 30, 40 and 50 includes a receiver 62 coupled to the respective receive antenna, a controllable amplifier 64 coupled to the respective receiver and also coupled to the respective programmable feed unit 38, 48 and 58, and a transmitter 66 coupled between the respective amplifier and the respective transmit antenna 34, 44 and 54. As discussed below, signal 68 is provided by generator 20 to the programmable feed unit, and signal 68 includes:

1. a noisy signal from generator 20 to the programmable feed unit;

2. a signal to control phase shifting of the noisy signal in the programmable feed unit; and

3. a signal to control attenuation of the noisy signal in the programmable feed unit.

The phase shifted and/or attenuated version of the noisy signal is then provided by the programmable feed unit to control the controllable amplifier 64 in the receiver unit. This ensures random noise is produced from the transmit antenna.

In operation, each device tends to oscillate on its own. A signal from the transmit antenna is picked up on the receive antenna. The signal picked up on the receive antenna is received in receiver 62, amplified in amplifier 64 and provided to transmitter 66 that is coupled the respective transmit antenna. When this loop provides enough gain, the device will oscillate. In fact, the proximity of the antennas pretty much ensures that the loop will have enough gain. Amplifier 64 may well provide fractional amplification or operate as an attenuator. This loop is adjust to have a loop gain from just below oscillation to just above oscillation when operated on its own. The receive antenna will pick up additional signals from other transmit antennas in system 10 and from reflections off nearby reflective surfaces. In addition, signals from the respective programmable feed device 38, 48 or 58, as discussed herein, are added into the loop at amplifier 64. The loop gain is adjusted to oscillate with a random noisy waveform in this environment.

In another variant of the first embodiment, either the transmit antenna or the receive antenna, or both, of first device 30 is a directional antenna directed toward a point inside the area to be protected, either the transmit antenna or the receive antenna, or both, of second device 40 is a directional antenna directed toward the point inside the area to be protected, and either the transmit antenna and the receive antenna, or both, of third device 50 is a directional antenna directed toward the point inside the area to be protected, hi operation, directing antenna gain inside the area to be protected tends to minimize collateral jamming effects outside of the desired area to be protected, and tends to minimize the power required from transmit antennas 34, 44 and 54 to achieve the desired level of jamming inside the area to be protected.

In another variant, the devices 30, 40 and 50 are located near a reflective surface or reflective surfaces that are characterized by a curvature. This produces reflected signals that appear to come from conjugate images of the transmit antennas of the devices.

In yet another variant, the devices 30, 40 and 50 are located near a reflective surface or reflective surfaces that are characterized by a curvature. The reflective surface includes any or all of the inside walls of an aircraft, the inside walls of a railroad car, the inside walls of bus, the walls of a subway tunnel, the walls of an automobile tunnel, and the walls of an auditorium, conference room, studio or the link. This also produces reflected signals that appear to come from conjugate images of the transmit antennas of the devices within the aircraft, the railroad car, the bus, the subway tunnel, the automobile tunnel, or the auditorium.

In another variant of the first embodiment, the generator produces a signal that is characterized by a center frequency. The generator includes a comb generator with a bandwidth greater than 20% of the center frequency and preferably grater than 50% of the center frequency. In practical systems, jamming of signals at frequencies of 312, 314, 316, 392, 398, 430, 433, 434 and 450 to 500 MHz may be desired. A center frequency of 400 MHz and a jamming bandwidth of 200 MHz (307 MHz to 507 MHz, a 50% bandwidth) would cover this range. A very suitable system for some application may be realized by jamming 430 through 500 MHz (a 20% bandwidth centered on 460 MHz). The frequency band from 312 through 316 MHz may be easily covered by a 2% bandwidth generator, and the 392 and 398 MHz frequencies may be easily covered by a generator with just a little more than 2% bandwidth. hi another variant of the first embodiment, the programmable feed unit in each device includes either a programmable attenuator coupled to the generator, a programmable phase shifter coupled to the generator, or both. In a version of this variant, where the programmable feed unit in each device includes the programmable attenuator, the programmable attenuator includes a variable gain amplifier characterized by a gain controlled by a signal from the generator. In another version of this variant, where the programmable feed unit in each device includes the programmable phase shifter, the programmable phase shifter may be mechanized with several designs.

In one design, the programmable phase shifter includes a network that includes a variable inductor where an inductance of the inductor is controlled by a signal from the generator. An example of such a variable inductor is a saturable inductor. A saturable inductor includes two coils wound around a common magnetic material such as a ferrite core. Through one coil, a bias current passes to bring the ferrite core in and out of saturation. The other coil is the inductor whose inductance is varied according to the bias current. The bias current is generated in generator 20, and it may be either a fix bias to set the phase shifting property or it may be a pulsed waveform to vary the phase shifting property.

In another design, the programmable phase shifter includes a network that includes a variable capacitor where a capacitance of the capacitor is controlled by a signal from the generator. A back biased varactor diode is an example of such a variable capacitor. hi yet another design, the programmable phase shifter includes a variable delay line where a delay of the delay line is controlled by a signal from the generator. A typical example of this type of delay line at microwave frequencies is a strip line disposed between blocks of ferrite material where the blocks of ferrite material are encircled by coils carrying a bias current so that the ferrite materials are subjected to a magnetizing force, hi this way, the propagation properties of strip line are varied according to the magnetizing force imposed by the current through the coil.

In yet another design, the programmable phase shifter includes two or more delay lines, each characterized by a different delay. The phase shifter further includes a switch to select an active delay line, from among the two or more delay lines, according to a signal from the generator.

Whatever the design that is used, the bias current or control signal is generated in generator 20. It may be either a fix voltage or current to set the phase shifting property of the programmable feed unit or it may be a pulsed waveform to vary the phase shifting property.

In another variant of the first embodiment, generator 20 is processor controlled. The processor may be a microprocessor or other processor. A memory stores the modes of operations in the form of a threat table that specifies such parameters as the center frequency and the bandwidth of the signals to be generated by generator 20 for each threat or application (e.g., tunnel, aircraft, railroad car, office auditorium, etc.) and stores the attenuation and phase shifting properties to be provided to each of the programmable feed units 38, 48 and 58. In a typical generator design, the threat table provides a center frequency for a radio frequency jamming signal and also proved a seed for a random number generator (e.g., digital key stream generator). The random numbers are used to generate a randomly chopped binary output waveform at about 5 to 20 times the center frequency that used as a chopping signal to modulate the signal at the center frequency. Many other types of noise generators may also be used. The output of the chopped center frequency signal is a broadband noise signal that is provided to each of the programmable feed units 38, 48 and 58.

In alternative variants, generator 20 includes circuits to generate additional randomly chopped binary output waveforms, according to parameters in the threat table, to control the variable attenuator and/or the variable phase shifter in each of the programmable feed units 38, 48 and 58. Alternatively, the threat table may store a fixed number, for each threat, to provide a fixed attenuation and a fixed phase shift in the programmable feed units 38, 48 and 58 that may be selected differently for each threat.

FIG. 3 shows an example of the coverage area achieved using an example of a jamming system according to the present invention that has four jamming devices disposed at the corners of a 1 km square, where the transmit antennas of each device are directional and pointed at the center of the area to be protected. Side lobes and back lobes of the transmit antennas are present but only at a greatly reduced gain so that collateral jamming is minimized, and the power required to cover the 1 km square is minimized by the use of overlapping main beam and near side lobe coverage. Standing waves that may produce dead zone in the coverage area are eliminated by the use of programmable feed units that can individually vary, and randomly vary in particular, the signal strength and phase of the signals originating from each transmit antenna. This produces an electronic countermeasure bubble (ECM bubble) with no gaps in coverage.

Having described preferred embodiments of a novel jamming system (which are intended to be illustrative and not limiting), it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is therefore to be understood that changes may be made hi the particular embodiments of the invention disclosed which are within the scope of the invention as defined by the appended claims.

Having thus described the invention with the details and particularity required by the patent laws, what is claimed and desired protected by Letters Patent is set forth in the appended claims.

Claims

What is claimed is:

1. A system comprising a generator and at least three devices located at respective vertices of an area to be protected, each device including: a transmit antenna; a receive antenna; an antenna unit; and a programmable feed unit coupled between the antenna unit and the generator.

2. A system according to claim 1, wherein the at least three devices includes first, second, third and fourth devices.

3. A system according to claim 1, wherein the antenna unit in each device includes: a receiver coupled to the respective receive antenna; an amplifier coupled to the respective receiver and coupled to the generator; and a transmitter coupled between the respective amplifier and the respective transmit antenna.

4. A system according to claim 1, wherein: at least one of the transmit antenna and the receive antenna of a first device is a directional antenna directed toward a point inside the area to be protected; at least one of the transmit antenna and the receive antenna of a second device is a directional antenna directed toward the point inside the area to be protected; and at least one of the transmit antenna and the receive antenna of a third device is a directional antenna directed toward the point inside the area to be protected.

5. A system according to claim 1, wherein the devices are located near a reflective surface with a curvature so as to produce reflected signals that appear to come from conjugate images of the transmit antennas of the devices.

6. A system according to claim 5, wherein the reflective surface includes at least one of: the inside walls of an aircraft; the inside walls of a railroad car; the inside walls of bus; the walls of a subway tunnel; the walls of an automobile tunnel; and the walls of a room.

7. A system according to claim 1, wherein: the generator produces a signal that is characterized by a center frequency; and the generator includes a comb generator with a bandwidth greater than 20% of the center frequency.

8. A system according to claim 7, wherein the generator includes a comb generator with a bandwidth greater than 50% of the center frequency.

9. A system according to claim 1, wherein the programmable feed unit in each device includes at least one of: a programmable attenuator coupled to the generator; and a programmable phase shifter coupled to the generator.

10. A system according to claim 9, wherein: the programmable feed unit in each device includes the programmable attenuator; and the programmable attenuator includes a variable gain amplifier characterized by a gain controlled by a signal from the generator.

11. A system according to claim 9, wherein the programmable feed unit in each device includes the programmable phase shifter.

12. A system according to claim 11, wherein the programmable phase shifter includes a network that includes a variable inductor where an inductance of the inductor is controlled by a signal from the generator.

13. A system according to claim 11, wherein the programmable phase snifter includes a network that includes a variable capacitor where a capacitance of the capacitor is controlled by a signal from the generator.

14. A system according to claim 11, wherein the programmable phase shifter includes a variable delay line where a delay of the delay line is controlled by a signal from the generator.

15. A system according to claim 11, wherein the programmable phase shifter includes: plural delay lines; and a switch to select an active delay line according to a signal from the generator.