|Publication number||USRE39759 E1|
|Application number||US 10/836,859|
|Publication date||Aug 7, 2007|
|Filing date||Apr 30, 2004|
|Priority date||Dec 3, 1984|
|Publication number||10836859, 836859, US RE39759 E1, US RE39759E1, US-E1-RE39759, USRE39759 E1, USRE39759E1|
|Inventors||Larry W. Fullerton|
|Original Assignee||Time Domain Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (85), Non-Patent Citations (24), Referenced by (81), Classifications (37)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application is a continuation of application Ser. No. 07/368,831, filed on Jun. 20, 1989; which is a continuation-in-part of application Ser. No. 07/192,475, filed on May 10, 1988; which is a continuation-in-part of application Ser. No. 06/870,177, filed on Jun. 3, 1986, now U.S. Pat. No. 4,743,906; which is a continuation-in-part of application Ser. No. 06/677,597, filed on Dec. 3, 1984, now U.S. Pat. No. 4,641,317.
This application is also a continuation-in-part of International Application No. PCT/US90/01174, filed on Mar. 2, 1990, which is a continuation-in-part of International Application No. PCT/US89/01020, filed on Mar. 10, 1989. Said PCT Application No. PCT/US89/01020 is also a continuation-in-part of U.S. application Ser. No. 07/010,440, filed on Feb. 3, 1987, now U.S. Pat. No. 4,813,057.
This invention relates generally to signal transmission systems, and particularly to a time domain system wherein spaced narrow signal bursts, impulses, or single cycles, or near single cycles sometimes referred to as monocycles of electromagnetic energy (radio or light) or sonic energy are transmitted in a compatible medium and where signals have wideband frequency content and wherein discrete frequency signal components are generally below noise level and are thus not discernable by conventional receiving equipment.
Transmissions by radio, light, and sonic energy have heretofore been largely approached from the point of view frequency content, or band of frequencies. Thus, and with respect to radio, coexistent different radio transmissions are permissible by means of assignment of different frequencies or frequency channels to different users, particularly those within the same geographic area. Essentially foreign to this concept is that of tolerating transmissions which are not frequency limited. While it would seem that the very notion of not limiting frequency response would create havoc with existing frequency denominated services, it has been previously suggested that such is not necessarily true and that, at least theoretically, it is possible to have overlapping use of the radio spectrum. One suggested mode is that provided wherein very short, on the order of one nanosecond or less, radio pulses are applied to a broadband antenna which ideally would respond by transmitting short burst signals, typically comprising three to four polarity lobes, which comprise, energywise, signal energy over essentially the upper entire band (above 100 megacycles) of the most frequently used radio frequency spectrum, that is, up to the midgigahertz region. A basic discussion of impulse effected radio transmission is contained in an article entitled “Time Domain Electromagnetics and Its Application,” Proceedings of the IEEE, Vol. 66, No. 3, March 1978. This article particularly suggests the employment of such technology for baseband radar, and ranges from 5 to 5,000 feet are suggested. As noted, this article appeared in 1978, and now ten years later, it is submitted that little has been accomplished by way of achieving commercial application of this technology.
From both a theoretical and an experimental examination of the art, it has become clear to the applicant that the lack of success have largely been due to several factors. One is that the extremely wide band of frequencies to be transmitted poses very substantial requirements on an antenna. Antennas are generally designed for limited frequency bandwidths, and traditionally when one made any substantial change in frequency, it became necessary to choose a different antenna or an antenna of different dimensions. This is not to say that broadband antennas do not, in general, exist, but in general, applicant is unaware of any prior practical structures which, when excited by very short impulses, respond by the transmission of burst signals as described above, the ideal for this field of transmission. This view is based upon having tested many antennas and from discussions with contemporaries who are basically still struggling with the problem.
Two antenna types have received attention as being reasonably good broadband radiators, or receivers—the bicone antenna and various forms of horn antennas, particularly wherein the antenna becomes an extension of a feed transmission line. The applicant has tested published versions of both and has found that they simply fail to meet the obvious goal of transmitting sufficiently short bursts. Recently, applicant has learned of an improved horn-type antenna with improved response. However, it is understood to be three-dimensionally large and thus appears impractical for most common uses.
A second problem which has plagued advocates of the employment of impulse or time domain technology for radio is that of effectively receiving and detecting the presence of the signal bursts, particularly in the presence of high levels of existing ambient radiation, present nearly everywhere. If one considers the problem simply in terms of competition with the ambient signals, it might appear insurmountable, and perhaps this is an explanation for the lack of progress in receiver technology in this field. The state of the art prior to applicant's entrance generally involved the employment of brute force detection, that of threshold or time threshold gate detection. Threshold detection simply enables passage of signals higher than a selected threshold level. The problem with this approach is obvious in that if one transmits impulse generated signals which are of sufficient amplitude to rise above ambient signal levels, the existing radio services producing the latter may be unacceptably interferred with. For some reason, perhaps because of bias produced by the wide spectrum of signal involved, e.g., from 50 MHz on the order of 5 GHz, the possibility of coherent detection has been thought impossible.
With respect to transmissions via light and sonic energy, conventional techniques similarly call for relatively narrow frequency band transmissions which require quite high spectral density of frequency energy, and this in turn has been, in certain applications, a disadvantage that can be detected by unintended receivers.
Accordingly, it is the object of this invention to provide an impulse or time domain (or baseband) transmission system which attacks all of the above problems and to provide a complete impulse time domain transmission system which, in the applicant's view, eliminates the known practical barriers to its employment, and, importantly, its employment for electromagnetic and sonic modes of radio transmission, including communications, telemetry, navigation, radar, and sonar.
With respect to radio signal transmissions, and as one aspect of applicant's invention, a transmitting antenna is basically formed quite opposite to the bicone antenna and wherein element configuration is reversed, the two elements of the antenna each being triangular in at least one X-Y dimension, and the bases of these elements being positioned closely adjacent.
As a second aspect of the invention, a radio transmitter is a pulse creating switching which is closely and directly connected to antenna element, thus eliminating transmission line effects which tend to undesirably lengthen the transmitted signal.
Third, by the combination of the applicant's antenna and transmitter configurations, bursts, near monocyclic pulses, having, for example, three to five polarity reversals, are transmitted and received.
As a further consideration, practical power restraints in the past have been generally limited to the application of a few hundred volts of applied signal energy to the transmitting antenna. This has been overcome by a transmitter switch which is formed by a normally insulating crystalline structure, such as diamond material sandwiched between two metallic electrodes, which are then closely coupled to the elements of the antenna. This material is switched to a conductive state by exciting it with an appropriate wavelength beam of light, ultraviolet in the case of diamond. In this manner, no metallic triggering communications line extends to the antenna which might otherwise pick up radiation and re-radiate it, adversely effecting signal coupling to the antenna and interfering with the signal radiated from it, both of which tend to prolong the length of a signal burst, a clearly adverse effect.
With respect to a radio receiver, as one aspect or feature of the invention, a like receiving antenna is employed to that used for transmission as described above. Second, a coordinately timed signal to that of the transmitted signal is either detected from the received signal, as in communications, dealt with in said U.S. Pat. No. 4,979,186, or telemetry, or received directly from the transmitter as, for example, in the case of radar. Then, the coordinately timed signal, typically a simple half cycle of energy, is mixed or multiplied with the received signal to determine modulation or position of a target at a selected range, as the case may be.
As still a further feature of this invention, transmitted burst signals are varied in time pattern (in addition to a modulation pattern for communications or telemetry). This greatly increases the security of the system and differentiates signals from nearly, if not all, ambient signals, that is, ambient signals which are not synchronous with transmitted burst signals, an effect readily achievable. This also enables the employment of faster repetition rates with radar which would, absent such varying or dithering, create range ambiguities as between returns from successive transmission and therefore ranges. Burst signals are signals generated when a stepped voltage change is applied to a broadband antenna, such as a reverse bicone, but flat, antenna.
It is significant to note that here that bursts signals may be generated, for example, by the application of a stepped voltage to a broadband radiator.
As still a further feature of this invention, the repetition rate of burst signals would be quite large, say, for example, up to 100 MHz, or higher, this enabling a very wide frequency dispersion, and thus for a given overall power level, the energy at any one frequency would be extremely small, thus effectively eliminating the problem of interference with existing radio frequency based services.
As still a further feature of this invention, moving targets are detected in terms of their velocity by means of the employment of a bandpass filter following mixing and double integration of signals. As a still further feature of the invention when employed in this latter mode, two channels of reception are ideally employed wherein the incoming signal is multiplied by a selected range, or timed, locally generated signal in one channel, and mixing the same incoming signal by a slightly delayed, locally generated signal in another channel, delay being on the order of 0.5 nanosecond. This accomplishes target differentiation without employing a separate series of transmissions.
As still another feature of this invention, multiple radiators or receptors would be employed in an array wherein their combined effect would be in terms of like or varied in time of sensed (or transmitted) output and to thereby accent either a path normal to the face of the antenna or to effect a steered path offset to a normal path accomplished by selected signal delay paths.
As still another feature of this invention, radio antenna elements would be positioned in front of a reflector wherein the distance between the elements and reflector is in terms of the time of transmission from an element or elements to reflector and back to element(s), typically about three inches, this being with a tip-to-tip dimension of elements of approximately nine inches.
As still another feature of the invention, wideband light, time domain, transmissions are enabled and particularly by the employment of a new and novel light frequency modulator.
Finally, and of very substantial significance, is that the light modulator referred to the preceding paragraph provides what is believed to be a breakthrough in conveniently enabling frequency modulation of light signals passing, for example, through a fiber optic having a variable refractive index with bias voltage. Additionally, it may be employed as a selectable delay device.
Referring to the drawings,
The transmitter is basically controlled by control 210. It includes a transmit sequence control portion 212 which determines the timing of transmitted signal bursts, at, for example, 10,000 bursts per second, in which case transmit sequence control 212 generates an output at 10,000 Hz on lead 214. Oscillator 216 is operated at a higher rate, for example, 20 MHz.
The signal output of transmit sequence control 212 is employed to select particular pulse outputs of oscillator 216 to be the actual pulse which is used as a master pulse for controlling both the output of transmitter 218 and the timing of receiver functions, as will be further described. In order to unambiguously and repetitively select an operative pulse with low timing uncertainty from oscillator 216, the selection is one and some fraction of an oscillator pulse interval after an initial signal from control 212. The selection is made via a control sequence employing D-type flip-flops 218, 220, and 222. Thus, the transmit sequence control pulse on lead 214 is applied to the clock input of flip-flop 218. This causes the Q output of flip-flop 218 to transition to a high state, and this is applied to a D input of flip-flop 220. Subsequently, the output of oscillator 216 imposes a rising edge on the clock input of flip-flop 220. At that time, the high level of the D input of this flip-flop is transferred to the Q output. Similarly, the Q output of flip-flop 220 is provided to the D input of flip-flop 222, and the next rising edge of the pulse from oscillator 216 will cause the not Q output of flip-flop 222 to go low and thus initiate the beginning of the transmit-receive cycle.
For the transmit mode, the not Q output of flip-flop 222 is fed as an input to analog programmable delay 213 and to counter 215. Counter 215, for example, would respond to the not Q outputs of flip-flop 222 and count up to a selected number, for example, 256, and recycle to count again. Its binary output would be fed as an address to memory unit 217, ROM or RAM, which would have stored, either in numerical address order, or randomly selected order, a number. As a result, upon being addressed, a discrete output number would be fed to D/A converter unit 221. D/A converter unit 221 would then provide an analog signal output proportional to the input number. This output is employed to sequentially operate programmable delay unit 213 for delays of pulses from flip-flop 222 by an amount proportional to the signal from D/A converter 221. The range of delays or modulation would typically be up to the nominal timing between pulses, in this case, up to 100 nanoseconds, and practically up to 99 nanoseconds. The delayed output of programmable delay unit 213 is then fed to fixed delay unit 224 which provides a fixed delay of 200 nanoseconds to each pulse that it receives. The thus delayed pulses are then fed to trigger generator 223. Trigger generator 223, e.g., an avalanche mode operated transistor, would provide a sharply rising electrical output at the 10,000 Hz rate or a like response of light output, e.g., by laser, depending upon the transmitter to be driven. In accordance with one feature of this invention, trigger generator 223 would be an ultraviolet laser, In any event, a pulse of trigger generator 223 is fed to and rapidly turns on a switch 225 which, for example, may again be an electrically operated or light operated switch, such as a diamond switch in response to the ultraviolet laser triggering device via fiber optic 227. Importantly, it must be capable of switching in a period of a nanosecond or less.
Conformal reverse bicone, but flat, antenna 200 is turned on or turned off, or successively both, by switch assembly 215 which applies stepped voltage changes to the antenna. It responds by transmitting essentially short burst or monocycle signals 229 each time that it is triggered. These burst signals are then transmitted into space via a directional version of antenna 200 as illustrated in
Signal returns from a target would be received by receiver 226, typically located near or together with transmitter 219, via receiving antenna 202, again, a conformal reverse bicone antenna. The received signals are amplified in amplifier 228 and fed to mixer 230, together with a signal from template generator 232, driven by delay line 236, which is timed to produce signals, typically half cycles in configuration, and corresponding in time to the anticipated time of arrival of a signal from a target at a selected range.
Mixer 230 functions to multiply the two input signals, and where there are coincidence signals, timewise and with like or unlike polarity coincident signals, there is a significant and integratable output. Since the goal here is to determine the presence or absence of a target based on a number of signal samplings as effected by integration, where a true target does not exist, the appearance of signals received by mixer 230 corresponding to the time of receipt of signals from template generator 232 will typically produce signals which vary not only in amplitude but also in polarity. It is to be borne in mind that the present system determines intelligence, not instantaneously, but after a period of time, responsive to a preponderance of coherent signals over time time, a facet of time domain transmissions. Next, it is significant that the template generator produce a template signal burst which is no longer than the effecting signal to be received and bear a consistent like or opposite polarity relationship in time with it. As suggested above, received signals which do not bear this relation to the template signal will be substantially attenuated. As one signal, the template signal is simply a one polarity burst signal. Assuming that it maintains the time relationship described, effective detection can be effected.
For purposes of illustration, we are concerned with looking at a single time slot for anticipated signal returns following signal bursts from transmitting antenna 225. Accordingly, template generator 232 is driven as a function of the timing of the transmitter. To accomplish this, coarse delay counter 235 and fine delay programmable delay line 236 are employed. Down counter 235 counts down the number of pulse outputs from oscillator 216 which occur subsequent to a control input on lead 238, the output of programmable delay unit 213. A discrete number of pulses thereafter received from oscillator 216 is programmable in down counter 235 by an output X from load counter 241 on lead 240 of control 210, a conventional device wherein a binary count is generated in control 210 which is loaded into down counter 235. As an example, we will assume that it is desired to look at a return which occurs 175 nanoseconds after the transmission of a signal from antenna 200. To accomplish this, we load into down counter 235 the number “7,” which means it will count seven of the pulse outputs of oscillator 216, each being spaced at 50 nanoseconds. So there is achieved a 350-nanosecond delay in down counter 235, but subtracting 200 nanoseconds as injected by delay unit 224, we will have really an output of down counter 235 occurring 150 nanoseconds after the transmission of a burst by transmitting antenna 200. In order to obtain the precise timing of 175 nanoseconds, an additional delay is effected by programmable delay line 236, which is triggered by the output of down counter 235 when its seven count is concluded. It is programmed in a conventional manner by load delay 242 of control 210 on lead Y and, thus in the example described, would have programmed programmable delay line 236 to delay an input pulse provided to it by 25 nanoseconds. In this manner, programmable delay line 236 provides a pulse output to template generator 232, 175 seconds after it is transmitted by bicone transmitting antenna 200. Template generator 232 is thus timed to provide, for example, a positive half cycle or square wave pulse to mixer 230 or a discrete sequence or pattern of positive and negative excursions.
The output of mixer 230 is fed to analog integrator 250. Assuming that there is a discrete net polarity likeness or unlikeness between the template signal and received signal during the timed presence of the template signal, analog integrator 250, which effectively integrates over the period of template signal, will provide a discrete voltage output. If the signal received is not biased with a target signal imposed on it, it will generally comprise as much positive content as negative content on a time basis; and thus when multiplied with the template signal, the product will follow this characteristic, and likewise, at the output of integrator 250, there will be as many discrete products which are positive as negative. On the other hand, with target signal content, there will be a bias in one direction or the other, that is, there will be more signal outputs of analog integrator 250 that are of one polarity than another. The signal output of analog integrator 250 is amplified in amplifier 252 and then, synchronously with the multiplication process, discrete signals emanating from analog integrator 250 are discretely sampled and held by sample and hold 254. These samples are then fed to A/D converter 256 which digitizes each sample, effecting this after a fixed delay of 40 microseconds provided by delay unit 258, which takes into account the processing time required by sample and hold unit 254. The now discrete, digitally calibrated positive and negative signal values are fed from A/D converter 256 to digital integrator 262 which then digitally sums them to determine whether or not there is a significant net voltage of one polarity or another, indicating, if such is the case, that a target is present at a selected range. Typically, a number of transmissions would be effected in sequence, for example, 10, 100, or even 1,000 transmissions, wherein the same signal transit time of reception would be observed, and any signals occurring during like transmissions would then be integrated in digital integrator 262, and in this way enable recovery of signals from ambient, non-synchronized signals which, because of random polarities, do not effectively integrate.
The output of digital integrator 262 would be displayed on display 264, synchronized in time by an appropriate signal from delay line 236 (and delay 256) which would thus enable the time or distance position of a signal return to be displayed in terms of distance from the radar unit.
By this arrangement, each of the 1 MHz pulses from divide-by-16 divider 402 is delayed a discrete amount. The pulse is then fed to fixed delay unit 408 which, for example, delays each pulse by 60 nanoseconds in order to enable sufficient processing time of signal returns by receiver 410. The output of fixed delay unit 408 is fed to trigger generator 412, for example, an avalanche mode operated transistor, which provides a fast rise time pulse. Its output is applied to switch 414, typically an avalanche mode operated transistor as illustrated in
Considering now receiver 410, antenna 412, identical with antenna 200, receives signal returns and supplies them to mixer 414. Mixer 414 multiplies the received signals from antenna 412 with locally generated ones from template generator 416. Template generator 416 is triggered via a delay chain circuitry of analog delay unit 406 and adjustable delay unit 418, which is set to achieve a generation of a template signal at a time corresponding to the sum of delays achieved by fixed delay 408 and elapsed time to and from a target at a selected distance. The output of mixer 414 is fed to short-term analog integrator 420 which discretely integrates for the period of each template signal. Its output is then fed to long-term integrator 422 which, for example, may be an active low-pass filter and integrates over on the order of 50 milliseconds, or, in terms of signal transmissions, up to, for example, approximately 50,000 such transmissions. The output of integrator 422 is amplified in amplifier 424 and passed through adjustable high-pass filter 426 to alarm 430. By this arrangement, only A.C. signals corresponding to moving targets are passed through the filters and with high-pass filter 426 establishing the lower velocity limit for a target and low-pass filter 428 determining the higher velocity of a target. For example, high-pass filter 426 might be set to pass targets moving at a greater velocity than 0.1 feet per second and integrator-low-pass filter 422 adapted to pass signals representing targets moving less than 50 miles per hour. Assuming that the return signals pass both such filters, alarm 430, which may be in any form of sensual indicator, aural or visual, would be operated.
By this technique, there is achieved real time differentiation between broad boundary objects, such as trees, and sharp boundary objects, such as a person. Thus, assuming that in one instant the composite return provides a discrete signal and later, for example, half a nanosecond later, there was no change in the scene, then there would be a constant difference in the outputs of mixers 450 and 452. However, in the event that a change occurred, as by movement of a person, there would be changes in difference between the signals occurring at the two different times, and thus there would be a difference in the output of differential amplifier 464. This output would then be fed to high-pass filter 426 (
In terms of a system as illustrated in
While the operation thus described involves a single perimeter, by a simple manual or automatic adjustment, observations at different ranges can be accomplished. Ranges can be in terms of a circular perimeter, or, as by the employment of a directional antenna (antenna 200 with a reflector), effect observations at a discrete arc.
An echo or reflection from a target of the signal transmitted by sonic transducer 502 would be received by a similarly configured sonic transducer 520, and its output would then be coupled via plates 512 and 514 to amplifier 228 and thence onto mixer 230 as illustrated in
It is believed of perhaps greater significance that light modulator 524, a frequency modulator, described above has many other applications, and particularly as an intelligence modulator of a laser beam. In such case, the laser input would typically be supplied in a continuous or spaced input, and the modulating waveform would be whatever was desired to mix with or impress on the laser beam.
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|U.S. Classification||342/27, 375/130, 375/256, 380/34, 342/21|
|International Classification||H04B1/717, H04B1/719, H04B1/7163, G01S7/292, H04B14/02, G01S13/18, G01S7/282, H01Q9/28, H01Q21/06, G01S13/02, H04L27/30, G01S13/04|
|Cooperative Classification||H04B1/71632, H04B14/026, H04B1/719, G01S13/0209, H01Q9/28, G01S7/282, H04B1/71637, G01S7/292, H04L27/103, H01Q21/061, H04B1/7174, G01S13/18|
|European Classification||H04B1/717C, H01Q21/06B, G01S7/282, G01S13/18, H04B14/02B, G01S13/02B, G01S7/292, H01Q9/28|