Patent Grant
8175512
1. Field of the Invention
The present invention relates to electronic countermeasure jamming systems that are capable of interrupting radio links from triggering devices used in connection with improvised explosive devices. In particular, the invention related to a look through mode for sensing the presence of radio links.
2. 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.
In 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.
Known omni directional systems radiate to provide 360 degree coverage on a plane with elevations plus or minus of the plane. Very few truly omni directional antenna systems are known to create coverage in three dimensions on a unit sphere. Difficulties are encountered that include, for example, the feed point through the sphere causes distortion of the radiation pattern, metal structures near the antenna cause reflections that distort the radiation pattern, and the individual radiating element of an antenna inherently does not produce a spherical radiation pattern. In addition, providing a spherical radiation pattern over a broad band of frequencies can be extremely difficult. Antenna structures intended to shape the radiation pattern at one frequency can cause distortion in the radiation pattern at another frequency.
A system includes a generator and at least one device. The generator includes a waveform oscillator and a blanking pulse generator. Each device includes a transmit antenna, a receive antenna, an antenna unit, a mixer and a detector. The antenna unit includes a receiver coupled to the receive antenna, an amplifier coupled to the receiver and a transmitter coupled to the transmit antenna and the blanking pulse generator. The mixer has inputs coupled to the amplifier and the waveform oscillator. The detector is coupled to the mixer.
The invention will be described in detail in the following description of preferred embodiments with reference to the following figures.
A new system for sensing RF signals operates in a look through mode in conjunction with a jamming system. The system, as more fully described below, includes a generator and at least one device. The generator includes a waveform generator and a blanking pulse generator. Each device includes at least two antennas, an antenna unit, a mixer and a detector. The antenna unit includes a receiver coupled to a receive antenna, an amplifier coupled to the receiver and a transmitter coupled to a transmit antenna and the blanking pulse generator. The mixer has inputs coupled to the amplifier and the waveform generator. The detector is coupled to the mixer.
In
In operation and as depicted in
Antenna 10 has a shape similar to a “bow tie” antenna, and it functions as a broad band antenna. The two halves of the “bow tie” are preferably disposed on opposite sides of the insulating substrate 12, but may, in other variations, be formed on the same side. Antenna 10 is preferably fed from an end point instead of a center point as is common with “bow tie” style antennas. However, in other variations, antenna 10 may be fed from other point, such as the center. In one variation of this antenna, the entire antenna is formed from a double sided copper clad epoxy-glass printed wiring board. In such case, conductor 30 is typically a plated through hole, but may be a rivet or pin held in place by solder filets 32 as depicted in
In
In operation, applied RF signal currents fed through coupler 64 pass though feed portions 72, 74 into ground bus 50 and radiating element 62. From there, electric fields extend between ground bus 50 and the radiating element 62 in such a way to cause RF signals to radiate from antenna 60.
In alternative embodiments, any one or more of antennas 80, 82 and 84 are similarly formed on the same insulating substrate. Each alternative antenna embodiment is varied by size and shape to meet frequency requirements and impedance matching requirements according to “radiator” technology. The size and shape of the feed portions 72, 74 are defined to match impedances from the coupler 64 to the radiating element of the antenna.
In
Antenna 90 further includes a tap conductor 106 coupled between the first signal conductor 96 of coupler 94 and a predetermined one of the plural turns of the wire 100. The predetermined turn number is determined during early design stages and may be easily defined by trying several different turn numbers and measuring the antenna's performance A first end of the plural turns of wire 100 is coupled to the second signal conductor 98.
In operation, applied RF signal currents fed through coupler 94 pass though conductor 96, through tap wire 106 to the predetermined one of the plural turns of wire 100, and from there through a portion of wire 100 to the first end of wire 100 to conductor 98. Additional turns of wire 100 beyond the driven turns between the first end of wire 100 and tap conductor 106 are parasitically driven.
In
The electronic modules may be placed in locations other than those depicted in
In a first embodiment of an antenna system, the antenna system includes plural antennas. Each antenna is different than every other antenna, and each antenna is characterized by a principal plane. A principal plane of a first antenna 230 is oblique to a principal plane of a second antenna. The second antenna may be located and oriented as depicted by antenna 240 or 250 in
In a first variant of the first embodiment of the antenna system, the second antenna is located and oriented as antenna 240 in
In an example of the first variant of the first embodiment of the antenna system and much as is described with respect to the antenna depicted in
In a first mechanization, the principal planes of the first and third antennas 230, 250 are oblique; and possibly substantially orthogonal.
In an example of the first mechanization, the principal planes of the second and third antennas 240, 250 are substantially parallel.
In a second mechanization, the principal planes of the second and third antennas 240, 250 are substantially parallel.
In a second variant of the first embodiment of the antenna system, the second antenna is located and oriented as antenna 250 in
In a second embodiment of an antenna system, the antenna system includes plural antennas. Each antenna is different than every other antenna, and each antenna is characterized by a principal plane. A principal plane of a first antenna is substantially parallel to a principal plane of a second antenna 240. Much as is described with respect to the antenna depicted in
In a first variant of the second embodiment of the antenna system, the first antenna is located and oriented as antenna 250 in
In a third embodiment of an antenna system, the antenna system includes plural antennas. Each antenna is different than every other antenna, and each antenna is characterized by a principal plane. A principal plane of a first antenna 250 is oblique to a principal plane of a second antenna. The second antenna may be located and oriented as depicted by antenna 230 in
In many variants of the above embodiments, antennas designed substantially similarly to the antenna depicted in
In many variants of the above embodiments, antennas designed substantially similarly to the antenna depicted at 60 in
In many variants of the above embodiments, antennas designed substantially similarly to the antenna depicted at 80 in
In many variants of the above embodiments, antennas designed substantially similarly to the antenna depicted at 82 in
In many variants of the above embodiments, antennas designed substantially similarly to the antenna depicted at 84 in
In many variants of the above embodiments, antennas designed substantially similarly to the antenna depicted in
In a jammer operation, the antennas are fed by signal oscillators. While known broadband jammers require noise generators, with the present invention, inexpensive oscillators may be used. It should be noted that spectral purity of the oscillator is not a requirement. Waveforms distorted from pure sinusoidal waveforms merely add to the broadband coverage. The several antennas, located in the near radiation field (i.e., within 5 to 10 wavelengths) from each other, add to the distortion giving rise to a broadband effect. Signals radiated from one antenna excite parasitic resonance in other nearby antennas. The oscillators for a frequency range from 400 MHz to 500 MHz, for a frequency range from 800 MHz to 900 MHz, for a frequency range from 1,800 MHz to 1,900 MHz, and for a frequency range from 2,400 MHz to 2,500 MHz are located in electronic module 226 of
The overall antenna system is intended to work with the oscillators to disrupt communications in selected bands. When considering design balancing, the need for portable operation and long battery life gives rise to a need for low transmit power. However, high transmit power is generally needed to jam a data link. Long battery life is best achieved by ensuring that the radiation intensity pattern is efficiently used. Coverage for the system described is intended to be omni directional in three dimensions. Thus, the best antenna pattern is achieved when there are no main lobes with great antenna gain and no notches with below normal antenna gain. For at least this reason, placement of the antennas and all conductive elements (e.g., electronic modules 224 and 226) are very important, a requirement that become all the more difficult when another requirement of broadband jamming is required in selected bands.
To meet these stringent requirements, the design process 300 includes measuring performance, analyzing the results and adjusting the antennas' location, orientation and individual antenna design. In
In
In
Another embodiment of a jamming system is depicted in
In a variant of the embodiment and as depicted in
1. an RF signal from generator 1020 to the programmable feed unit;
2. a signal to control phase shifting of the RF signal in either the programmable feed unit or in the controllable amplifier of the antenna unit or both; and
3. a signal to control attenuation of the RF signal in either the programmable feed unit or in the controllable amplifier of the antenna unit or both.
The phase shifted and/or attenuated version of the RF signal is then provided by the programmable feed unit to control the controllable amplifier 1064 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 1062, amplified in amplifier 1064 and provided to transmitter 1066 that is coupled the respective transmit antenna. When this loop provides enough gain, the device will oscillate. In fact, the proximity of the antennas helps ensure that the loop will have enough gain. Amplifier 1064 may well provide fractional amplification or operate as an attenuator. This loop is adjusted 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 1010 and from reflections off nearby reflective surfaces. In addition, signals from the respective programmable feed device 1038, 1048 or 1058, as discussed herein, are added into the loop at amplifier 1064. The loop gain is adjusted to oscillate with a random noisy waveform in this environment.
In another variant of the 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 greater 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.
In 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 might include 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 1020, 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.
In 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. In 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 1020. It may be either a fixed 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 embodiment, generator 1020 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 1020 for each threat or application and stores the attenuation and phase shifting properties to be provided to each of the programmable feed units 1038, 1048 and 1058. 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 is 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 1038, 1048 and 1058.
In alternative variants, generator 1020 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 1038, 1048 and 1058. 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 1038, 1048 and 1058 that may be selected differently for each threat.
In yet another variant of the embodiment and as depicted in
Antenna unit 1136 of driven device 1130 includes a programmable balun 1162 coupled to receive an RF signal from programmable feed device 1138 and functioning to split the signal from feed device 1138 into two phase diverse signals to drive respective controllable amplifiers 1164, 1184. The respective amplified signals, call them left and right amplified signals, out of respective controllable amplifiers 1164 and 1184 feed respective transmitters 1166 and 1186. The left and right transmit signals out of respective transmitters 1166 and 1186 are coupled to respective left and right transmit antennas 1132 and 1134. Right transmit antenna 1134 may be the same or similar to transmit antenna 1034 of
As discussed above with respect to
1. a signal to control phase shifting of the RF signal in the programmable feed unit as discussed below;
2. a signal to control attenuation of the RF signal; and
3. an RF signal from generator 1020 to the programmable feed unit; however, the RF signal from generator 1020 will be modulated upon a sweeping RF carrier signal as distinguished from the device depicted in
Balun 1132 is a signal splitter that outputs to controllable amplifiers 1164, 1184 signals distinguished by phase. If the phase difference were 90 degrees and the phase centers of the antennas 1132, 1134 were coincident, the result would be a circular polarized wave originating at the antenna phase center. However, the antenna phase centers are separated by a distance and the actual phase difference between the outputs of the balun is controlled by the signal to control phase shifting of the RF signal that is part of the signals provided in signal 1068. In fact, the generator may advantageously provide a randomly varying signal to control phase shifting of the RF signal. This random variation provides greater distortion observable at any point within the area of protection.
The signal to control attenuation of the RF signal that is part of the signals provided in signal 1068 may control the gain and/or attenuation of the RF signal as it passes through programmable feed unit 1138. Alternatively, the signal to control attenuation of the RF signal that is part of the signals provided in signal 1068 may advantageously include two separately controllable gain/attenuation control signals that pass through programmable feed unit 1138, are split by balun 1132 so that individual and separately controllable gain/attenuation control signals are coupled to control respective controllable amplifiers 1164 and 1184.
Unlike device 1030 discussed above with respect to
In
Typically, generator 1220 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 (or the frequency minimum and the frequency maximum) of the signals to be generated by generator 1220 for each threat or application and stores the attenuation and phase shifting properties to be provided to each of the programmable feed units within driven devices 1230, 1240 and 1250. The center frequency and bandwidth (or the frequency minimum and the frequency maximum) for each threat is provided to respective ones of modulators 1224, 1226 and 1228 to generate desired frequencies, and the outputs of modulators 1224, 1226 and 1228 are provided to respective ones of driven devices 1230, 1240 and 1250 as the signal carried within the bundle of signals discussed above as signal 1068. The processor, memory and the phase and amplitude control signals discussed above are not depicted in
In alternative variants, generator 1220 may include circuits to generate randomly varying attenuation and phase shift, or may include circuits to generate fixed attenuation and phase shift, 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 1038, 1048 and 1058 of driven devices 1230, 1240 and 1250 that may be selected differently for each threat.
Typically, waveform generator 1220 is processor controlled. The processor may be a microprocessor or other processor. A memory stores the modes of operations, typically in the form of a threat table that specifies such parameters as the frequency minimum and the frequency maximum (or the center frequency and the bandwidth) of the signals to be generated by each of the band specific modulators 1224, 1226, 1228. For example, the memory might store low frequency F-Lo and high frequency F-Hi values to generate the waveform depicted in
In addition, the memory preferably stores the attenuation and phase shifting properties to be provided to each of the programmable feed units within driven devices 1230, 1240 and 1250. The values for these attenuation and phase shifting properties are retrieved from the memory and provided either in digital form, or converted to analog form, to control the variable attenuator and/or the variable phase shifter in each of the programmable feed units 1038, 1048 and 1058 of driven devices 1230, 1240 and 1250 as a signal contained in the bundle of signals 1068 (
Each VCO 1290 in each of the several band is likely to have its own unique conversion relationship to convert the voltage in to frequency out. The threat table, or a separate resources calibration table, includes the parameters for an equation to convert each specific voltage to a specific frequency. Typically, when the conversion is linear as it is over reasonably narrow bandwidths, two parameters are required: an offset reference (e.g., V0, f0) and a slope (e.g., ΔV/Δf). However, when a VCO is pushed to its limits, the conversion equation from voltage to frequency may include a third parameter for a quadratic factor. In any event, waveform generator 1280 provides the voltage as signal 1282 that is necessary for VCO 1290 to convert the voltage to a desired frequency modulated waveform signal 1292, for example covering the desired band in a triangle waveform depicted in
Frequency modulated waveform signal 1292 varies from a low frequency end of the band, F-Lo, to a high frequency end of the band, F-Hi. The triangle wave repeats on a cycle with a period T. Testing has revealed that the triangle waveform is superior for disrupting communication signals when compared to a frequency stepped waveform. As an example, the repeat period of the triangle waveform, a period T, is preferably about 1.5 milliseconds when F-Lo is 3 MHz and F-Hi is 500 MHz.
In yet another embodiment, frequency modulated waveform signal 1292 is caused to dwell for a longer period at a particular frequency to address an important threat within the band of any one of the band specific modulators 1224, 1226, 1228. In
In the frequency band of segments 1 and 6, frequencies are scanned at a rate of 693 MHz per millisecond. In the frequency band of segments 2 and 5, frequencies are scanned at a rate of 100 MHz per millisecond. In the frequency band of segments 3 and 4, frequencies are scanned at a rate of 320 MHz per millisecond. Therefore, it can be seen that the frequency segment from 315 to 320 MHz is scanned at a slower rate, seems to dwell on these segments, than the other segments. It can now be seen that frequency modulated waveform signal 1292 can be customized by selecting parameters for Table 1 so that any one segment, or multiple segments, may be dwelled on when threats in those frequency ranges are anticipated. After the scan of one segment is complete, the next segment as indicated in Table 1 is begun. Table 1 is exemplary only and could be enlarged to include additional frequency segments. Typically, the threat table includes Table 1 plus stored values to control the variable attenuator and/or the variable phase shifter in the corresponding one of the programmable feed units 1038, 1048 and 1058 of driven devices 1230, 1240 and 1250.
The above described jamming system provides distorted signals to jam selected communications links. As a signal is radiated from one antenna, the signal is reflected or absorbed and re-radiated (i.e., scattered) from another antenna, even an out of band antenna. The proximity of the several antennas causes the scattering effects to multiply and form a more or less spherical radiation coverage pattern. Such a radiation jamming system may be mounted as an active unit on a vehicle and provide a bubble of protection around the vehicle.
In the active unit, the threat table is loaded based on recent intelligence about the communication links that needs to be jammed When the power levels associated with a particular communication link are such that more average power is needed to jam the link, the dwell time at or near the frequency of the particular communications link is extended relative to the repeat period of the entire waveform by designing a frequency segment as discussed above for an extended dwell.
In yet another embodiment, the several VCOs are designed to have a fast frequency slewing property sometimes called frequency settling time. When such slew rates are fast enough, the slope between two frequencies in
In yet another embodiment, a look through mode is implemented. In the look through mode, all transmitters are silenced, blocked or blanked using a blanking pulse of a predetermined blanking period, for example, 15 milliseconds. Transmitter 1066 (
In this embodiment, mixer 1294 (
In operation, signals on receive antenna 1032 pass through receiver 1062 and through controllable amplifier 1064 (see
If the antenna units are of a driven device design depicted in
In yet another embodiment is depicted in
In operation, frequency modulated waveform signal 1292 is frequency shifted (either up or down) by a frequency of an intermediate frequency, i.e., the frequency of local oscillator 1291. The output of mixer 1294 is the desired signal modulated on the intermediate frequency defined by the frequency of local oscillator 1291. If the intermediate frequency is carefully chosen (e.g., the IF of AM or FM audio radio receivers), the component and certainly the technology of these components are easily available. Then, mixer 1295 frequency shifts (either down or up, but the opposite of mixer 1293) by the intermediate frequency defined by local oscillator 1291 to deliver a baseband signal to baseband detector 1298.
Using the embodiment depicted in either
In yet another embodiment, a reactive unit and an active unit are mounted on the same vehicle and coupled together with a tether through which the blanking pulse from the reactive unit is transmitted to the active unit in order to blank all transmitters in the active unit. The reactive unit continues reactive jamming, as discussed above, concentrated on the selected few threats to be jammed and providing increased power density and “service” frequency to the frequency segments of selected few threats to be jammed. The active unit continues active jamming programs, as discussed above with respect to Table 1, with the sole exception that the transmitters in the active unit are blanked during “sniff mode” of the reactive unit as indicated by the blanking pulse received over the tether. In this way, threats requiring higher power densities are serviced by the reactive unit when and if detected, but the active unit continues to jam all threats generally known to exist in the region of operation of the vehicle carrying the active and reactive units.
Having described preferred embodiments of a novel look through mode of a 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 in 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.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2007/086975 | 12/10/2007 | WO | 00 | 1/26/2010 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2009/048480 | 4/16/2009 | WO | A |
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| Number | Date | Country |
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| WO 2006020864 | Feb 2006 | WO |
| PCTUS2007086975 | Jun 2009 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20100128761 A1 | May 2010 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60873588 | Dec 2006 | US |
