CA1293038C - Detector system - Google Patents
Detector systemInfo
- Publication number
- CA1293038C CA1293038C CA000576023A CA576023A CA1293038C CA 1293038 C CA1293038 C CA 1293038C CA 000576023 A CA000576023 A CA 000576023A CA 576023 A CA576023 A CA 576023A CA 1293038 C CA1293038 C CA 1293038C
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- CA
- Canada
- Prior art keywords
- circuit
- detector
- coupled
- azimuth
- detector device
- Prior art date
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/4804—Auxiliary means for detecting or identifying lidar signals or the like, e.g. laser illuminators
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/481—Constructional features, e.g. arrangements of optical elements
- G01S7/4818—Constructional features, e.g. arrangements of optical elements using optical fibres
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- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Optics & Photonics (AREA)
- Computer Networks & Wireless Communication (AREA)
- General Physics & Mathematics (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- Optical Radar Systems And Details Thereof (AREA)
Abstract
ABSTRACT
The present invention relates to a laser warning sensor with transit time coding of the directions of incidence by light conductors, wherein only the resolution in azimuth or resolution both in azimuth as well as in elevation, is achieved by means of an appropriate arrangement of the light conductors.
Definition of the time reference point through the zero transit of a laser-excited oscillation of an oscillation circuit and the suppression of false alarms through correlation of signals in the start and stop channel is hereby accomplished. An almost trouble-free detector system is provided hereby, which permits precise angular determination without any need for a time datum point circuit.
The present invention relates to a laser warning sensor with transit time coding of the directions of incidence by light conductors, wherein only the resolution in azimuth or resolution both in azimuth as well as in elevation, is achieved by means of an appropriate arrangement of the light conductors.
Definition of the time reference point through the zero transit of a laser-excited oscillation of an oscillation circuit and the suppression of false alarms through correlation of signals in the start and stop channel is hereby accomplished. An almost trouble-free detector system is provided hereby, which permits precise angular determination without any need for a time datum point circuit.
Description
1'~93038 The present invention relates to a detector system for the directional interception and detection of laser radiations, this having at least a first and a second detector stage, each of which incorporates an opto-electrical converter, with a plurality of individual lenss (optical systems), which together cover a prescribed overall solid angle, wherein the solid angle of the adjacent individual optical systems overlap one another, and wherein the individual optical systems are each arranged in the azimuth plane, with a first and a second light conductor for each individual optical system, wherein each of the light conductors leads to a first and a second detector stage, wherein all of the first light conductors are of the same length and lead to the first detector stage, whereas the second light conductors that lead to the second detector stage are of different lengths, and their lengths are graduated in the azimuth angular direction in order to form various transit times, and with a transit time measurement system that is connected with the first and second detector stages, in order to establish the start and end of transit time measurement and the azimuth angle of the incoming laser radiation, which is a function of this. Hereinafter, the azimuth plane is taken to be a horizontal plane in which the azimuth angle is measured.
Laser radiation that takes place in the visible or infrared light range, is used for a variety of purposes and in a variety of _ 3 ~ 38 applications in the military field. Most frequently, pulsed or intensity-modulated laser radiation is used for ranye measurement in fire-control systems, to illuminate a target for target identification of a missile sensor, and for the direct control of missiles, this being done in conjunction with laser guidance beams.
In order that timely defensive measures can be initiated against such aggressive laser radiation, the type of the threat must be established in advance. To this end, it is necessary to detect the laser radiation at the target itself, and also to identify it against the background of spurious radiation. It is also necessary to analyse the characteristic features of this laser radiation, such as, for example, its wave length and signature with regard to pulse length and pulse repitition frequency. For deliberate countermeasures, which can be passive -- such as deceptive change of location by false targets and the use of smoke -- or active in the form of back-reflection or engagement it is particularly necessary to arrive at a precise measurement of the direction from which the laser radiation is arriving at the target.
For many various types of targets, such as, for example, vehicles, ships, helicopters, aircraft, and satellites, different demands are made with regard to the width of the solid angle that lZ~3Q3~3 is covered and the angular resolution of a warning sensor in azimuth and in elevation. Thus, for example, for vehicles in the field, such as, for example, tanks and trucks, one anticipates mainly a threat from an angular range close to the horizontal plane (e.g., from other tanks or low-flying helicopters). The range of detection thus lies in an angular range of 360 in elevation and in an angular range of +30 in elevation.
Hereinafter, the elevation plane is taken to be every plane that is perpendicular to the azimuth plane and in which the angle of elevation is measured.
Since vehicles constantly change their position about the horizontal axis due to irregularities in the terrain, precise angular measurement of a source of laser radiation in the elevation direction in relation to the coordinate system of the vehicle is less important, whereas angular measurements in each azimutal plane must be exact.
The movements of vehicles about the vertical axis are much slower. This means that azimuth measurements retain their validity over a significantly longer time span. The source of laser radiation can be precisely defined with the help of additional means, such as means that are used for visual observation of the terrain. However, in order that the detection of sources of laser radiation is possible in each movement position of the vehicle, the complete sensitivity of the radiation sensor throughout the overall required elevation _ 5 _ ~ ~3~3~
range must be assured. This means that the radiation sensor must cover the whole azimuth-elevation range continuously and with no gaps.
For other targets, for example, helicopters, aircraft and satellites, because of the greater mobility of such targets in the various solid angle ranges, and because of the various possible rotational movements, the situation differs from that described above. Here both precise angular resolution in azimuth as well as in elevation is important. In most instances, the required and desired solid angle range is 360 in azimuth and i90 in elevation.
Apart from the various demands for the angular detection of laser warning sensors it is desirable that the user be able to establish the most varied sources of laser radiation using one and the same piece of equipment.
With regard to the very large number of various military sources of laser radiation in the area of short-wave visible light up to and including radiation in the thermal infrared range, the radiation detectors may not be restricted in their spectral sensitivity and reception readiness by filters that are arranged in front of the photodetectors, in which connection these filters in and of themselves serve to reduce interference (noise) caused - 6 ~ 93~
by background lighting. Such filters automatically reduce the spectral sensitivity of such opto-electrical sensors.
In particular, the wave length ranges for frequency-shifted excimer lasers are from 0.4 ~m, for ruby lasers, 0.69 ~m, for laser diodes 0.85 ~m to 0.95 ~m, for alexandrite lasers 0.75 ~m to 0.85 ~m, for Nd:YAG 1.06 ~m and 1.32 ~m, for Nd:YAG methan Raman shifted 1.52 ~m, for erbium 1.65 ~m, for holmium 2.12 ~m, for deuterium fluoride 3.6 ~m to 4.0 ~m, for CO2 lasers 9.5 ~m to 11.5 ~m. On the other hand, because of the mobility of the target objects under the most varied lighting conditions the laser radiation detections must operate faultlessly and without breakdown. It must also be ensured that when sunlight shines directly into the field of vision of the radiation sensor, the false-warning rate remains low. Such laser radiation sensors must also be unaffected by other sources of artificial light, from which no laser radiation is emitted, such as, for example, stroboscopes, photo flashes, gun fire, fiare bombs, light flashes, and the like.
A very large dynamic signal range must also be intercepted by the detector system, in order to ensure that the detector system operates without failure in the most varied weather conditions, at different distances between the warning sensor and the source of radiation when the pulse energy of the laser is changing, when the laser radiation strikes the target in various impact areas, _ 7 _ lZ93~38 and during turbulance fluctuations in the atmosphere, they must also operate over the whole radiation sector. In addition, it must at the same time be possible to avoid interference to angular measurements caused by secondary reflections of the laser radiation in the vicinity and at the target.
The detector system mentioned in the introduction hereto is described in DE-PS 33 23 828 and in DE-OS 35 25 518. The direction of the incoming laser radiation is established and determined with the help of transit-time measurement [timing the interval between the transmission and echo return (see Gnst, p.
521) -- Tr.], when the laser radiation passes through fibre optic light conductors. To this end, two light conductors are used behind a common individual optical system. Depending on the size of the solid angle that is to be covered, there can be numerous such individual optical systems. Adjacent individual optical systems cover overlapping individual areas of the solid angle.
All of the first light conductors of the individual optical systems lead to a first detector which, when a laser pulse or pulses arrive, activates a transit-time measurement circuit. All of the second light conductors, which are each of a different length which are connected to a second detector, by means of the counter circuit that has been initiated is stopped. The counter circuit will be stopped earlier or later, depending on the direction of radiation that is established. These light conductors serve as delay lines for the laser radiation. The - 8 - lZ93~38 time differential between the start and the stop of the counter circuit is a metric for the angle in azimuth. Since a plurality of the light conductor pairs are provided in conjunction with the individual optical system to control the time measurement circuit, and adjacent individual optical systems overlap with regard to their solid angle, panoramic surveillance and complete coverage of the solid angle is ensured. Since all of the first light conductors are of the same length, each start pulse occurs at the same time after the arrival of a laser pulse. In reality, laser radiation passes to the associated pair of light conductors not only through one individual optical system, but also through the adjacent optical systems to the pairs of light conductors located behind these. This means, that the second detector stage receives not only a Main pulse through the individual optical system and the associated second light conductor, through which the strongest radiation arrives but, in addition, weaker laser signals are also detected through the adjacent optical systems and second light conductors. Because of this, in addition to the main laser pulse one also receives a weaker lead pulse and a weaker trailing pulse. ~ow, in order to ascertain the precise solid angle of the incoming radiation in azimuth, an interpolation operation is carried out in order to determine the time datum point of these three received pulses. Appropriate computing operations are required to do this, as is described in greater detail in DE-OS 35 25 518.
9 ~293~38 It is the task of the present invention to create a detector system of the type described in the introduction hereto, which permits precise angular determination based on transit-time measurement in a simple manner, without any need for a time and costly datum point circuit. Furthermore, the effect of interfering (noise) signals is to be kept as small as possible.
According to the present invention, this task has been solved in that the opto-electrical converters of the first and second detector stages are each connected with a damped oscillating circuit; and in that the duration of the rise phase of a resonance oscillation until it reaches an amplitude is greater or equal to the typical duration or rise time of a laser pulse that arrives at at least one individual optical system; and in that a zero transit detection stage is subsidiary in each instance to the damped oscillating circuit of the first and second detector stage and in each instance on a first zero transit or one of the subsequent zero transits of the damped oscillations in question generates a start or stop signal for the transit-time measurement circuit.
A very simple electronic detector system has been created in this way; this delivers a clear time reference point for transit-time measurement, both for the incoming laser pulse and also for the time-delayed laser pulse for determination of the azimuth angle.
1293~38 Even if laser radiation falls on two or three adjacent individual optical systems and light conductors, very precise determination of the azimuth angle takes place by formation of a time reference point of the damped oscillations of the oscillation circuit.
Because of the fact that the duration of the resonance period or the resonant frequency is suitably selected, namely, i5 greater than the duration or rise time of the incoming laser pulse by approximately a factor of four, the phase position of the harmonic total signal is strictly correlated with the time reference point of the laser pulse signal. If, for example, two pulses at an interval that is smaller than one quarter of the period duration of the harmonic damped oscillation arrive at the detector, automatic superpositioning is effected such that the resulting harmonic oscillation is correlated with the common reference point. This means that a clear time reference for the measurement of the transit-time differential between the undelayed and the delayed laser pulse is created through measurement of the first or second or subsequent zero transits of the damped harmonic oscillation. Interpolation between two adjacent pulses takes place automatically.
A further advantage of the invention lies in the fact that the method of operation of the detector system is independent of the pulse amplitude, since processing is effected in the linear range of the opto-electrical converter (photodiode). No falsification 1293(~!38 of the phase caused by possible non-linear amplifications of the signal occur. It is possible to cover a very wide dynamic signal range of, for example, greater than 120 dB.
The damped oscillating circuit with the defined resonance frequency acts as a selective filter with a defined band width.
Signals within the range of the resonant frequency are passed with very little damping, whereas frequency components of the signals that are outside the band width are greatly damped.
Particularly during military applications of laser technology, laser pulses at a width between 10 ns to 200 ns, or long pulses with pulse lengths in the range of microseconds to seconds are used. However, as a rule, such long pulses have very short rise times in the range from 50 to 200 ns.
Compared to other rapid light processes with rise times greater than a few microseconds, laser pulses have oscillation frequency components of considerably higher frequency. This means, that with a selective oscillating filter that is tuned to a fixed or mean basic frequency of the laser pulse, this basic frequency including the adjacent frequency components of other light processes that lie within the band width can be effectively separated.
~293~3~
According to a further embodiment, laser pulse components with a width of T cause a resonance effect in the damped oscillator circuit if the resonant frequency of this is inversely proportional to the eight-fold value of the laser pulse width.
Proceeding from the above-discussed width of the laser pulse, this will result in an optimum oscillating frequency in the range of a few MHz.
According to a further configuration, an error-signal circuit is incorporated, and this has a time-window stage that can be affected by the first and second detector stage, and which generates a blocking signal for the transit-time measurement circuit or a subsidiary analysis circuit, if the time between the start signal and the stop signal i5 greater than the maximum transit-time differential between the longest of two light conductors and the first light conductor. This results in the advantage that time measurement is then only initiated and analysed if the start signal and the stop signal lie within the time window. According to a further configuration, a threshhold-value stage with a variable trigger threshhold is subsidiary to the first damped oscillating circuit of the first and second detector stage and this can be varied by an interference signal detector circuit in which the frequency of the interference-signal peaks, e.g., such as caused by noise peaks in particular from background illumination and by which the - 13 - 12~3~38 trigger threshhold is appropriately controlled. In this way, the probability of a false alarm is greatly reduced. Since the probability of determining signals at the opto-electrical converter depends, in the case of weak laser pulses, on the level to which the trigger threshhold has been set, this results in the advantage that, for example, in the case of low level daylight the sensitivity of the system is significantly greater than it is in sunlight, both in the visible and in the infrared sensitivity range of the opto-electrical converter.
In a most advantageous manner, the two zero passage detector stages or threshhold value stages are connected with a digital logic circuit. The transit-time measurement circuit is most expediently a counter circuit that is timed by an oscillator.
According to a further advantageous configuration, each of the individual optical systems also has an additional third light conductor; each of these third light conductors of the optical systems in the same elevation plane that is perpendicular to the azimuth plane is of a different length and they are graduated as viewed in the direction of the angle of elevation, and lead to a third detector stage, which is in like manner connected to a damped oscillating circuit. This results in the possibility of carrying out precise determination of the angle of the arriving laser radiation, not only in azimuth, but also in elevation.
12~3~3B
According to a further configuration, all three light conductors in the azimuth plane are of the same length. This means that the sensitivity viewed in the direction of elevation is equal, regardless of the azimuth angle position of the incom-ing laser radiation.
According to a further configuration, all the second light conductors of one elevation plane are of equal length.
This means that the sensitivity in azimuth is independent of the elevation direction of the laser radiation that has been deter-mined.
In this way, in a most advantageous manner, one obtains simultaneously and equally great angular resolution in azimuth as well as in elevation. This is of particular significance for the detection of airborne targets. In this manner, for each light conductor bundle series in elevation there is an equal light conductor bundle series in azimuth. Each of the two light bundle series has a subsidiary detector stage to generate a stop signal.
For the transit-time measurement circuit, for measurement of the transmit-time differential both in elevation and in azimuth there is a common detector stage to generate the start signal.
In accordance with the present invention, there is provided a detector device for detecting the presence and ori-ginating location of laser radiation comprising a plurality of discrete optics, each discrete optic being capable of detecting laser radiation over a certain solid angle, the solid angle of each discrete optics overlapping the solid angle of its neighbors, ~2~3C3~
- 14a - 26648-5 and the discrete optics being arranged in azimuth planes; first and second wave guide coupled to each discrete optics, with all first wave guides being of identical length and the lengths of the second wave guides being of increasing length in the direction of increasing azimuth angle in order to form different transit times; first and second detector stages having opto-electrical transducers and coupled respectively to the first and second wave guides; and transit time measuring circuit coupled to the first and second detector stage which determines the total time between detection by the first detector stage and the second detector stage and consequently the azimuth angle of the incident laser radiation; wherein the opto-electrical transducers of the first and second detector stage are coupled to respective damped resonant circuits, the resonant circuits requiring greater or equal amounts of time to reach maximum am~plitude than the respec-tive time to reach maximum amplitude of one laser pulse on at least one of the discrete optics and the damped resonant circuits being coupled to passage-through-the-zero-axis detectors, the detectors providing start and stop signals to the transit time measuring circuit.
The invention will be described in greater detail below on the basis of an exemplary embodiment shown in figures 1 to 4.
These are as follows:
1293~38 igure 1: a schematic diagram of the detector system with individual optical systems and light conductors arranged in the azimuth and in the elevation plane;
Figure 2: a cross section through a sensor head of the detector system;
Figure 3a, 3b: laser signal processing in the associated detector stage;
Figure 4: a schematic circuit diagram for signal processing and analysis.
Figure 1 shows a sensor head 1 of a detector system. This sensor head is a spherical housing which has a plurality of openings in the azimuth direction and in the elevation direction. Within these housing openings there are individual optical systems which, in figure 1, are numbered 2 as a common reference for all these individual optical systems. In the particular azimuth plane and in the elevation planes the individual optical systems form groups for subsequent analysis. Behind each of the individual optical systems there are three light conductors. The end of the particular light conductor is arranged in the focal plane or image plane of each individual optical system 2. The first light conductor of the first optical system of the uppermost azimuth plane is numbered Llll, whereas the first light conductor of this plane which is shifted by 180 is numbered Llln. The first light conductor of the first optical system of - 16 - ~Z93c38 the azimuth plane beneath this is numbered L121, etc. The first light conductor of the first optical system of the lowest azimuth plane is numbered Llnl, whereas the light conductor that is shifted through 180 is numbered Llnn. All of these first light conductors Llll to Llnn are of the same length and pass in a bundle to a lens 3, that serves to form the face end on a detector system 4. This detector system or stage 4 is designated as the start stage.
The second light conductor of the first optical system of the uppermost azimuth plane is numbered L211, whereas the light conductor that is shifted through 180 is numbered L21n. The second light conductor of the first optical system of the lowest azimuth is numbered L2nl, whereas the light conductor that is shifted through 180 bears the number L2nn. The second light conductors L211 to L2nl located in a common elevation plane are formed into light conductor bundles and pass to a second receiving lens 5, which forms the face ends of this light conductor on a second detector stage. These second light conductors L211 to L2nl of the first elevation plane are all of equal length. As can be seen from figure 1, the first individual optical systems are perpendicular to the azimuth plane.
The individual second light conductors of the optical systems that are shifted by 180 relative to the previously discussed ~Z93~38 first optical systems lie in a common elevation plane, and which are numbered L21n to L2nn are lead as a bundle to the same receiver lens 5. These are all of equal length. However, these light conductors are longer than the previously discussed light conductors of the first individual optical systems. The same applies to the individual second light conductors of those individual optical systems which lie in each instance in a common elevation plane and which subtend an azimuth angle relative to the first individual optical systems.
This means, that in each azimuth plane, equally high sensitivity and resolution of an incoming laser pulse is possible as a function of the particular azimuth angle. The detector stage 6 is also designated as a first stop stage. The graduated length differentials between the light conductors of adjacent elevation planes are equally great. This means that the measured length differential relative to the first light conductor constitutes a metric for the azimuth angle at which an incoming laser pulse impinges on the spherical head of the detector system.
The third light conductor of the first individual optical system of the uppermost azimuth plane is numbered L311, whereas the third light conductor of the same plane that is shifted through 180 is numbered L31n. All the light conductors L311 to L31n are formed into a bundle and passed to the receiver lens 7, which - 18 - ~Z93~3~
forms the face-bundle end on a detector stage 8, which is also designated as the second stop stage. The light conductors L
to L31n are of equal length.
The third light conductor of the first optical system of the lowest azimuth plane is numbered L3n1. The light conductor of the same plane that is shifted through 180 bears the reference number L3nn. These light conductors L3n1 to L3nn are formed into a bundle and passed to the above-mentioned receiver or imaging lens 7, so that its face end is also formed on the third detector stage 8 (second stop stage). These light conductors L3n1 to L3nn are of different lengths. However, the length of this light conductor bundle is different relative to the length of the light conductors of the first azimuth plane. It is also possible that the length gradation of the individual light conduetors of the various azimuth planes can be effected in a different manner.
Thus, it is for example, possible, that the equator plane of the spherical head is considered as the azimuth plane of origin and that the corresponding third light conductors of this plane are of a first length, whereas the lengths of the light conductor groups of the azimuth planes above and below this in symmetry are each of equal length. The graduation is selected accordingly.
Figure 2 shows a cross section through the spherical sensor head 1, which is in partial section. Those parts that correspond to 3~31~
the parts shown in figure 1 bear the same reference numbers.
In figure 3a, the first light conductors Llll to Llnn lead to the imaging lens 3 in order to form the face ends of this light conductor on a photodiode 9. The photodiode 9 is conducted in series with a damped oscillating circuit that consists of a coil 10, a condenser 11, and a resistance 12. This parallel oscillating circuit is also connected to the amplifier 13, at the output of one there is a current flow I. A laser pulse L is transmitted through the light conductor bundle Llll to Llnn and this pulse has the flow of current in time that is shown in figure 3. It is assumed that the width of this laser pulse is 50 ns. The period of the damped oscillator circuit is so selected that it is four times the value of the pulse duration T = 50 ns. This means that the resonant frequency for the damped oscillator circuit is 5 MHz. The damped oscillation curve of the current of the damped oscillation circuit is also shown in figure 3a. In a subsequent stage, not shown in figure 3a, the first zero transit I40 of the damped oscillation is established and used as a start signal for a counter circuit that is shown in figure 4.
Figure 3b shows the second light conductor bundle L211 to L2nn, that leads to the image lens 5 of the detector stage (first stop stage) 6. The photodiode of this detector stage is numbered 14.
The photodiode 14 is connected to a damped oscillator circuit, which consists of a resistance 15, a coil 16, and a condenser 17.
3~38 This oscillator circuit has a resonant frequency which is equal to the resonant frequency of the oscillating circuit shown in figure 3a. This means that the two oscillating circuits are configured identically. The follow-up amplifier is numbered 18.
As can be seen from figure 3b, because of the longer configuration of the light conductors the laser pulse arrives at the receiving lens 5 and consequently to the photodiode 14 after a delay. The damped oscillation starts after a corresponding delay. The first zero transit of this damped oscillation is designated I60- This first zero transit is delayed relative to the first zero transit of the undelayed damped oscillation as in figure 3a. The difference between both first zero transits is the delay time, which constitutes a metric for the azimuth angle of the incoming laser beam.
In figure 4, the parts that are identical to the ones shown in the preceding figures bear the same reference numbers. The start channel is formed by the first light conductors Llll to Llnn in con~unction with the first detector stage 5, the oscillating circuits 10, 11, and 12, and the follow-up amplifier 13, as well as a subsequently incorporated threshhold value stage 20 with a variable response level.
The second channel or also the first stop channel is configured by the second light conductors L211 to L2nn, the second detector - 21 _ 1~93Q38 stage (first stop stage), with the photodiode 14, the oscillating circuits 15, 16, and 17, the follow-up amplifier 18 and a subsequently incorporated threshhold value stage 21 with a variable response level. The outputs of the two threshhold value stages 20 and 21 an emitter coupled logic circuit 22, in which analog to digital conversion of the received signals is carried out. In addition, a zero transit determination is carried out within this switching stage 22. This emitter coupled logic circuit 22 has a subsidiary counter circuit 23, that is timed by means of an oscillator 24. The counter circuit 23 is connected at the output side with a microcomputer 25, this having control outputs that lead to the control inputs of the threshhold value circuits 20 and 21. Using this microcomputer 25, the threshhold value is automatically controlled as a function of the background lighting in order to avoid noise signals as far as possible.
Laser radiation that takes place in the visible or infrared light range, is used for a variety of purposes and in a variety of _ 3 ~ 38 applications in the military field. Most frequently, pulsed or intensity-modulated laser radiation is used for ranye measurement in fire-control systems, to illuminate a target for target identification of a missile sensor, and for the direct control of missiles, this being done in conjunction with laser guidance beams.
In order that timely defensive measures can be initiated against such aggressive laser radiation, the type of the threat must be established in advance. To this end, it is necessary to detect the laser radiation at the target itself, and also to identify it against the background of spurious radiation. It is also necessary to analyse the characteristic features of this laser radiation, such as, for example, its wave length and signature with regard to pulse length and pulse repitition frequency. For deliberate countermeasures, which can be passive -- such as deceptive change of location by false targets and the use of smoke -- or active in the form of back-reflection or engagement it is particularly necessary to arrive at a precise measurement of the direction from which the laser radiation is arriving at the target.
For many various types of targets, such as, for example, vehicles, ships, helicopters, aircraft, and satellites, different demands are made with regard to the width of the solid angle that lZ~3Q3~3 is covered and the angular resolution of a warning sensor in azimuth and in elevation. Thus, for example, for vehicles in the field, such as, for example, tanks and trucks, one anticipates mainly a threat from an angular range close to the horizontal plane (e.g., from other tanks or low-flying helicopters). The range of detection thus lies in an angular range of 360 in elevation and in an angular range of +30 in elevation.
Hereinafter, the elevation plane is taken to be every plane that is perpendicular to the azimuth plane and in which the angle of elevation is measured.
Since vehicles constantly change their position about the horizontal axis due to irregularities in the terrain, precise angular measurement of a source of laser radiation in the elevation direction in relation to the coordinate system of the vehicle is less important, whereas angular measurements in each azimutal plane must be exact.
The movements of vehicles about the vertical axis are much slower. This means that azimuth measurements retain their validity over a significantly longer time span. The source of laser radiation can be precisely defined with the help of additional means, such as means that are used for visual observation of the terrain. However, in order that the detection of sources of laser radiation is possible in each movement position of the vehicle, the complete sensitivity of the radiation sensor throughout the overall required elevation _ 5 _ ~ ~3~3~
range must be assured. This means that the radiation sensor must cover the whole azimuth-elevation range continuously and with no gaps.
For other targets, for example, helicopters, aircraft and satellites, because of the greater mobility of such targets in the various solid angle ranges, and because of the various possible rotational movements, the situation differs from that described above. Here both precise angular resolution in azimuth as well as in elevation is important. In most instances, the required and desired solid angle range is 360 in azimuth and i90 in elevation.
Apart from the various demands for the angular detection of laser warning sensors it is desirable that the user be able to establish the most varied sources of laser radiation using one and the same piece of equipment.
With regard to the very large number of various military sources of laser radiation in the area of short-wave visible light up to and including radiation in the thermal infrared range, the radiation detectors may not be restricted in their spectral sensitivity and reception readiness by filters that are arranged in front of the photodetectors, in which connection these filters in and of themselves serve to reduce interference (noise) caused - 6 ~ 93~
by background lighting. Such filters automatically reduce the spectral sensitivity of such opto-electrical sensors.
In particular, the wave length ranges for frequency-shifted excimer lasers are from 0.4 ~m, for ruby lasers, 0.69 ~m, for laser diodes 0.85 ~m to 0.95 ~m, for alexandrite lasers 0.75 ~m to 0.85 ~m, for Nd:YAG 1.06 ~m and 1.32 ~m, for Nd:YAG methan Raman shifted 1.52 ~m, for erbium 1.65 ~m, for holmium 2.12 ~m, for deuterium fluoride 3.6 ~m to 4.0 ~m, for CO2 lasers 9.5 ~m to 11.5 ~m. On the other hand, because of the mobility of the target objects under the most varied lighting conditions the laser radiation detections must operate faultlessly and without breakdown. It must also be ensured that when sunlight shines directly into the field of vision of the radiation sensor, the false-warning rate remains low. Such laser radiation sensors must also be unaffected by other sources of artificial light, from which no laser radiation is emitted, such as, for example, stroboscopes, photo flashes, gun fire, fiare bombs, light flashes, and the like.
A very large dynamic signal range must also be intercepted by the detector system, in order to ensure that the detector system operates without failure in the most varied weather conditions, at different distances between the warning sensor and the source of radiation when the pulse energy of the laser is changing, when the laser radiation strikes the target in various impact areas, _ 7 _ lZ93~38 and during turbulance fluctuations in the atmosphere, they must also operate over the whole radiation sector. In addition, it must at the same time be possible to avoid interference to angular measurements caused by secondary reflections of the laser radiation in the vicinity and at the target.
The detector system mentioned in the introduction hereto is described in DE-PS 33 23 828 and in DE-OS 35 25 518. The direction of the incoming laser radiation is established and determined with the help of transit-time measurement [timing the interval between the transmission and echo return (see Gnst, p.
521) -- Tr.], when the laser radiation passes through fibre optic light conductors. To this end, two light conductors are used behind a common individual optical system. Depending on the size of the solid angle that is to be covered, there can be numerous such individual optical systems. Adjacent individual optical systems cover overlapping individual areas of the solid angle.
All of the first light conductors of the individual optical systems lead to a first detector which, when a laser pulse or pulses arrive, activates a transit-time measurement circuit. All of the second light conductors, which are each of a different length which are connected to a second detector, by means of the counter circuit that has been initiated is stopped. The counter circuit will be stopped earlier or later, depending on the direction of radiation that is established. These light conductors serve as delay lines for the laser radiation. The - 8 - lZ93~38 time differential between the start and the stop of the counter circuit is a metric for the angle in azimuth. Since a plurality of the light conductor pairs are provided in conjunction with the individual optical system to control the time measurement circuit, and adjacent individual optical systems overlap with regard to their solid angle, panoramic surveillance and complete coverage of the solid angle is ensured. Since all of the first light conductors are of the same length, each start pulse occurs at the same time after the arrival of a laser pulse. In reality, laser radiation passes to the associated pair of light conductors not only through one individual optical system, but also through the adjacent optical systems to the pairs of light conductors located behind these. This means, that the second detector stage receives not only a Main pulse through the individual optical system and the associated second light conductor, through which the strongest radiation arrives but, in addition, weaker laser signals are also detected through the adjacent optical systems and second light conductors. Because of this, in addition to the main laser pulse one also receives a weaker lead pulse and a weaker trailing pulse. ~ow, in order to ascertain the precise solid angle of the incoming radiation in azimuth, an interpolation operation is carried out in order to determine the time datum point of these three received pulses. Appropriate computing operations are required to do this, as is described in greater detail in DE-OS 35 25 518.
9 ~293~38 It is the task of the present invention to create a detector system of the type described in the introduction hereto, which permits precise angular determination based on transit-time measurement in a simple manner, without any need for a time and costly datum point circuit. Furthermore, the effect of interfering (noise) signals is to be kept as small as possible.
According to the present invention, this task has been solved in that the opto-electrical converters of the first and second detector stages are each connected with a damped oscillating circuit; and in that the duration of the rise phase of a resonance oscillation until it reaches an amplitude is greater or equal to the typical duration or rise time of a laser pulse that arrives at at least one individual optical system; and in that a zero transit detection stage is subsidiary in each instance to the damped oscillating circuit of the first and second detector stage and in each instance on a first zero transit or one of the subsequent zero transits of the damped oscillations in question generates a start or stop signal for the transit-time measurement circuit.
A very simple electronic detector system has been created in this way; this delivers a clear time reference point for transit-time measurement, both for the incoming laser pulse and also for the time-delayed laser pulse for determination of the azimuth angle.
1293~38 Even if laser radiation falls on two or three adjacent individual optical systems and light conductors, very precise determination of the azimuth angle takes place by formation of a time reference point of the damped oscillations of the oscillation circuit.
Because of the fact that the duration of the resonance period or the resonant frequency is suitably selected, namely, i5 greater than the duration or rise time of the incoming laser pulse by approximately a factor of four, the phase position of the harmonic total signal is strictly correlated with the time reference point of the laser pulse signal. If, for example, two pulses at an interval that is smaller than one quarter of the period duration of the harmonic damped oscillation arrive at the detector, automatic superpositioning is effected such that the resulting harmonic oscillation is correlated with the common reference point. This means that a clear time reference for the measurement of the transit-time differential between the undelayed and the delayed laser pulse is created through measurement of the first or second or subsequent zero transits of the damped harmonic oscillation. Interpolation between two adjacent pulses takes place automatically.
A further advantage of the invention lies in the fact that the method of operation of the detector system is independent of the pulse amplitude, since processing is effected in the linear range of the opto-electrical converter (photodiode). No falsification 1293(~!38 of the phase caused by possible non-linear amplifications of the signal occur. It is possible to cover a very wide dynamic signal range of, for example, greater than 120 dB.
The damped oscillating circuit with the defined resonance frequency acts as a selective filter with a defined band width.
Signals within the range of the resonant frequency are passed with very little damping, whereas frequency components of the signals that are outside the band width are greatly damped.
Particularly during military applications of laser technology, laser pulses at a width between 10 ns to 200 ns, or long pulses with pulse lengths in the range of microseconds to seconds are used. However, as a rule, such long pulses have very short rise times in the range from 50 to 200 ns.
Compared to other rapid light processes with rise times greater than a few microseconds, laser pulses have oscillation frequency components of considerably higher frequency. This means, that with a selective oscillating filter that is tuned to a fixed or mean basic frequency of the laser pulse, this basic frequency including the adjacent frequency components of other light processes that lie within the band width can be effectively separated.
~293~3~
According to a further embodiment, laser pulse components with a width of T cause a resonance effect in the damped oscillator circuit if the resonant frequency of this is inversely proportional to the eight-fold value of the laser pulse width.
Proceeding from the above-discussed width of the laser pulse, this will result in an optimum oscillating frequency in the range of a few MHz.
According to a further configuration, an error-signal circuit is incorporated, and this has a time-window stage that can be affected by the first and second detector stage, and which generates a blocking signal for the transit-time measurement circuit or a subsidiary analysis circuit, if the time between the start signal and the stop signal i5 greater than the maximum transit-time differential between the longest of two light conductors and the first light conductor. This results in the advantage that time measurement is then only initiated and analysed if the start signal and the stop signal lie within the time window. According to a further configuration, a threshhold-value stage with a variable trigger threshhold is subsidiary to the first damped oscillating circuit of the first and second detector stage and this can be varied by an interference signal detector circuit in which the frequency of the interference-signal peaks, e.g., such as caused by noise peaks in particular from background illumination and by which the - 13 - 12~3~38 trigger threshhold is appropriately controlled. In this way, the probability of a false alarm is greatly reduced. Since the probability of determining signals at the opto-electrical converter depends, in the case of weak laser pulses, on the level to which the trigger threshhold has been set, this results in the advantage that, for example, in the case of low level daylight the sensitivity of the system is significantly greater than it is in sunlight, both in the visible and in the infrared sensitivity range of the opto-electrical converter.
In a most advantageous manner, the two zero passage detector stages or threshhold value stages are connected with a digital logic circuit. The transit-time measurement circuit is most expediently a counter circuit that is timed by an oscillator.
According to a further advantageous configuration, each of the individual optical systems also has an additional third light conductor; each of these third light conductors of the optical systems in the same elevation plane that is perpendicular to the azimuth plane is of a different length and they are graduated as viewed in the direction of the angle of elevation, and lead to a third detector stage, which is in like manner connected to a damped oscillating circuit. This results in the possibility of carrying out precise determination of the angle of the arriving laser radiation, not only in azimuth, but also in elevation.
12~3~3B
According to a further configuration, all three light conductors in the azimuth plane are of the same length. This means that the sensitivity viewed in the direction of elevation is equal, regardless of the azimuth angle position of the incom-ing laser radiation.
According to a further configuration, all the second light conductors of one elevation plane are of equal length.
This means that the sensitivity in azimuth is independent of the elevation direction of the laser radiation that has been deter-mined.
In this way, in a most advantageous manner, one obtains simultaneously and equally great angular resolution in azimuth as well as in elevation. This is of particular significance for the detection of airborne targets. In this manner, for each light conductor bundle series in elevation there is an equal light conductor bundle series in azimuth. Each of the two light bundle series has a subsidiary detector stage to generate a stop signal.
For the transit-time measurement circuit, for measurement of the transmit-time differential both in elevation and in azimuth there is a common detector stage to generate the start signal.
In accordance with the present invention, there is provided a detector device for detecting the presence and ori-ginating location of laser radiation comprising a plurality of discrete optics, each discrete optic being capable of detecting laser radiation over a certain solid angle, the solid angle of each discrete optics overlapping the solid angle of its neighbors, ~2~3C3~
- 14a - 26648-5 and the discrete optics being arranged in azimuth planes; first and second wave guide coupled to each discrete optics, with all first wave guides being of identical length and the lengths of the second wave guides being of increasing length in the direction of increasing azimuth angle in order to form different transit times; first and second detector stages having opto-electrical transducers and coupled respectively to the first and second wave guides; and transit time measuring circuit coupled to the first and second detector stage which determines the total time between detection by the first detector stage and the second detector stage and consequently the azimuth angle of the incident laser radiation; wherein the opto-electrical transducers of the first and second detector stage are coupled to respective damped resonant circuits, the resonant circuits requiring greater or equal amounts of time to reach maximum am~plitude than the respec-tive time to reach maximum amplitude of one laser pulse on at least one of the discrete optics and the damped resonant circuits being coupled to passage-through-the-zero-axis detectors, the detectors providing start and stop signals to the transit time measuring circuit.
The invention will be described in greater detail below on the basis of an exemplary embodiment shown in figures 1 to 4.
These are as follows:
1293~38 igure 1: a schematic diagram of the detector system with individual optical systems and light conductors arranged in the azimuth and in the elevation plane;
Figure 2: a cross section through a sensor head of the detector system;
Figure 3a, 3b: laser signal processing in the associated detector stage;
Figure 4: a schematic circuit diagram for signal processing and analysis.
Figure 1 shows a sensor head 1 of a detector system. This sensor head is a spherical housing which has a plurality of openings in the azimuth direction and in the elevation direction. Within these housing openings there are individual optical systems which, in figure 1, are numbered 2 as a common reference for all these individual optical systems. In the particular azimuth plane and in the elevation planes the individual optical systems form groups for subsequent analysis. Behind each of the individual optical systems there are three light conductors. The end of the particular light conductor is arranged in the focal plane or image plane of each individual optical system 2. The first light conductor of the first optical system of the uppermost azimuth plane is numbered Llll, whereas the first light conductor of this plane which is shifted by 180 is numbered Llln. The first light conductor of the first optical system of - 16 - ~Z93c38 the azimuth plane beneath this is numbered L121, etc. The first light conductor of the first optical system of the lowest azimuth plane is numbered Llnl, whereas the light conductor that is shifted through 180 is numbered Llnn. All of these first light conductors Llll to Llnn are of the same length and pass in a bundle to a lens 3, that serves to form the face end on a detector system 4. This detector system or stage 4 is designated as the start stage.
The second light conductor of the first optical system of the uppermost azimuth plane is numbered L211, whereas the light conductor that is shifted through 180 is numbered L21n. The second light conductor of the first optical system of the lowest azimuth is numbered L2nl, whereas the light conductor that is shifted through 180 bears the number L2nn. The second light conductors L211 to L2nl located in a common elevation plane are formed into light conductor bundles and pass to a second receiving lens 5, which forms the face ends of this light conductor on a second detector stage. These second light conductors L211 to L2nl of the first elevation plane are all of equal length. As can be seen from figure 1, the first individual optical systems are perpendicular to the azimuth plane.
The individual second light conductors of the optical systems that are shifted by 180 relative to the previously discussed ~Z93~38 first optical systems lie in a common elevation plane, and which are numbered L21n to L2nn are lead as a bundle to the same receiver lens 5. These are all of equal length. However, these light conductors are longer than the previously discussed light conductors of the first individual optical systems. The same applies to the individual second light conductors of those individual optical systems which lie in each instance in a common elevation plane and which subtend an azimuth angle relative to the first individual optical systems.
This means, that in each azimuth plane, equally high sensitivity and resolution of an incoming laser pulse is possible as a function of the particular azimuth angle. The detector stage 6 is also designated as a first stop stage. The graduated length differentials between the light conductors of adjacent elevation planes are equally great. This means that the measured length differential relative to the first light conductor constitutes a metric for the azimuth angle at which an incoming laser pulse impinges on the spherical head of the detector system.
The third light conductor of the first individual optical system of the uppermost azimuth plane is numbered L311, whereas the third light conductor of the same plane that is shifted through 180 is numbered L31n. All the light conductors L311 to L31n are formed into a bundle and passed to the receiver lens 7, which - 18 - ~Z93~3~
forms the face-bundle end on a detector stage 8, which is also designated as the second stop stage. The light conductors L
to L31n are of equal length.
The third light conductor of the first optical system of the lowest azimuth plane is numbered L3n1. The light conductor of the same plane that is shifted through 180 bears the reference number L3nn. These light conductors L3n1 to L3nn are formed into a bundle and passed to the above-mentioned receiver or imaging lens 7, so that its face end is also formed on the third detector stage 8 (second stop stage). These light conductors L3n1 to L3nn are of different lengths. However, the length of this light conductor bundle is different relative to the length of the light conductors of the first azimuth plane. It is also possible that the length gradation of the individual light conduetors of the various azimuth planes can be effected in a different manner.
Thus, it is for example, possible, that the equator plane of the spherical head is considered as the azimuth plane of origin and that the corresponding third light conductors of this plane are of a first length, whereas the lengths of the light conductor groups of the azimuth planes above and below this in symmetry are each of equal length. The graduation is selected accordingly.
Figure 2 shows a cross section through the spherical sensor head 1, which is in partial section. Those parts that correspond to 3~31~
the parts shown in figure 1 bear the same reference numbers.
In figure 3a, the first light conductors Llll to Llnn lead to the imaging lens 3 in order to form the face ends of this light conductor on a photodiode 9. The photodiode 9 is conducted in series with a damped oscillating circuit that consists of a coil 10, a condenser 11, and a resistance 12. This parallel oscillating circuit is also connected to the amplifier 13, at the output of one there is a current flow I. A laser pulse L is transmitted through the light conductor bundle Llll to Llnn and this pulse has the flow of current in time that is shown in figure 3. It is assumed that the width of this laser pulse is 50 ns. The period of the damped oscillator circuit is so selected that it is four times the value of the pulse duration T = 50 ns. This means that the resonant frequency for the damped oscillator circuit is 5 MHz. The damped oscillation curve of the current of the damped oscillation circuit is also shown in figure 3a. In a subsequent stage, not shown in figure 3a, the first zero transit I40 of the damped oscillation is established and used as a start signal for a counter circuit that is shown in figure 4.
Figure 3b shows the second light conductor bundle L211 to L2nn, that leads to the image lens 5 of the detector stage (first stop stage) 6. The photodiode of this detector stage is numbered 14.
The photodiode 14 is connected to a damped oscillator circuit, which consists of a resistance 15, a coil 16, and a condenser 17.
3~38 This oscillator circuit has a resonant frequency which is equal to the resonant frequency of the oscillating circuit shown in figure 3a. This means that the two oscillating circuits are configured identically. The follow-up amplifier is numbered 18.
As can be seen from figure 3b, because of the longer configuration of the light conductors the laser pulse arrives at the receiving lens 5 and consequently to the photodiode 14 after a delay. The damped oscillation starts after a corresponding delay. The first zero transit of this damped oscillation is designated I60- This first zero transit is delayed relative to the first zero transit of the undelayed damped oscillation as in figure 3a. The difference between both first zero transits is the delay time, which constitutes a metric for the azimuth angle of the incoming laser beam.
In figure 4, the parts that are identical to the ones shown in the preceding figures bear the same reference numbers. The start channel is formed by the first light conductors Llll to Llnn in con~unction with the first detector stage 5, the oscillating circuits 10, 11, and 12, and the follow-up amplifier 13, as well as a subsequently incorporated threshhold value stage 20 with a variable response level.
The second channel or also the first stop channel is configured by the second light conductors L211 to L2nn, the second detector - 21 _ 1~93Q38 stage (first stop stage), with the photodiode 14, the oscillating circuits 15, 16, and 17, the follow-up amplifier 18 and a subsequently incorporated threshhold value stage 21 with a variable response level. The outputs of the two threshhold value stages 20 and 21 an emitter coupled logic circuit 22, in which analog to digital conversion of the received signals is carried out. In addition, a zero transit determination is carried out within this switching stage 22. This emitter coupled logic circuit 22 has a subsidiary counter circuit 23, that is timed by means of an oscillator 24. The counter circuit 23 is connected at the output side with a microcomputer 25, this having control outputs that lead to the control inputs of the threshhold value circuits 20 and 21. Using this microcomputer 25, the threshhold value is automatically controlled as a function of the background lighting in order to avoid noise signals as far as possible.
Claims (12)
1. A detector device for detecting the presence and ori-ginating location of laser radiation comprising a plurality of discrete optics, each discrete optic being capable of detecting laser radiation over a certain solid angle, the solid angle of each discrete optics overlapping the solid angle of its neighbors, and the discrete optics being arranged in azimuth planes;
first and second wave guide coupled to each discrete optics, with all first wave guides being of identical length and the lengths of the second wave guides being of increasing length in the direction of increasing azimuth angle in order to form different transit times;
first and second detector stages having opto-electrical transducers and coupled respectively to the first and second wave guides; and transit time measuring circuit coupled to the first and second detector stage which determines the total time between detection by the first detector stage and the second detector stage and consequently the azimuth angle of the incident laser radiation;
wherein the opto-electrical transducers of the first and second detector stage are coupled to respective damped resonant circuits, the resonant circuits requiring greater or equal amounts of time to reach maximum amplitude than the respec-tive time to reach maximum amplitude of one laser pulse on at least one of the discrete optics and the damped resonant circuits being coupled to passage-through-the-zero-axis detectors, the detectors providing start and stop signals to the transit time measuring circuit.
first and second wave guide coupled to each discrete optics, with all first wave guides being of identical length and the lengths of the second wave guides being of increasing length in the direction of increasing azimuth angle in order to form different transit times;
first and second detector stages having opto-electrical transducers and coupled respectively to the first and second wave guides; and transit time measuring circuit coupled to the first and second detector stage which determines the total time between detection by the first detector stage and the second detector stage and consequently the azimuth angle of the incident laser radiation;
wherein the opto-electrical transducers of the first and second detector stage are coupled to respective damped resonant circuits, the resonant circuits requiring greater or equal amounts of time to reach maximum amplitude than the respec-tive time to reach maximum amplitude of one laser pulse on at least one of the discrete optics and the damped resonant circuits being coupled to passage-through-the-zero-axis detectors, the detectors providing start and stop signals to the transit time measuring circuit.
2. The detector device of claim 1, further comprising an evaluating circuit coupled to said first and second detector stages, the evaluating circuit having a time window circuit which monitors the signals from the first and second detector stages and an error signal circuit coupled to the time window circuit, the error signal circuit generating an error signal if the time between the start and stop signals is greater than the calculated maximum transit time difference between a first wave guide and the longest second wave guide, the evaluating circuit being capable of triggering a switching process if the number of detected error signals exceeds a preset number.
3. The detector device of claim 1 wherein the damped resonant circuits have a resonance period of between four and eight times the value of the longer of the laser pulse duration or the time to reach maximum amplitude of the laser pulse.
4. The detector device of claim 3, wherein a first and second threshold value circuit, with variable trigger threshold is coupled to the first and second passage-through-the-zero-axis detectors, the variable trigger threshold being adjusted by an interference signal circuit coupled to the threshold value circuits, the interference signal circuit being capable of determining the interference signal peaks and adjusting the variable trigger thresholds.
5. The detector device of claim 4 wherein the output from the threshold value circuits are coupled to a digital logic circuit.
6. The detector device of claim 5 wherein the transit time measuring circuit is comprised of a counter circuit clocked by an oscillator.
7. The detector device of claim 6 wherein the counter circuit is coupled to a microc-mputer, the microcomputer being coupled to the first and second threshold value circuits and cap-able of adjusting the threshold value.
8. The detector device of claim 1 wherein a third wave guide is coupled to each discrete optics, the third wave guides coupled to discrete optics in the same elevation plane being of increasing length in the increasing elevation angle direction, each of the third wave guides being coupled to a third detector stage, said third detector stage having a damped resonant circuit.
9. The detector device of claim 8, wherein all third wave guides on the same azimuth plane are of equal length.
10. The detector device of claim 9 wherein all second wave guide on the same elevation plane are of equal length.
11. The detector device of claim 10 wherein the transit times of the second and third wave guides are processed in separate channels and use separate identifiers.
12. The detector device of claim 3 wherein the resonance frequency of the damped resonant circuit is between 1 and 5 maga-hertz and the damped resonant circuit has a bandwidth of 10 to 200 nanoseconds.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000576023A CA1293038C (en) | 1988-08-30 | 1988-08-30 | Detector system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000576023A CA1293038C (en) | 1988-08-30 | 1988-08-30 | Detector system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1293038C true CA1293038C (en) | 1991-12-10 |
Family
ID=4138639
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000576023A Expired - Fee Related CA1293038C (en) | 1988-08-30 | 1988-08-30 | Detector system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1293038C (en) |
-
1988
- 1988-08-30 CA CA000576023A patent/CA1293038C/en not_active Expired - Fee Related
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