DE3114600C2 - - Google Patents

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Publication number
DE3114600C2
DE3114600C2 DE19813114600 DE3114600A DE3114600C2 DE 3114600 C2 DE3114600 C2 DE 3114600C2 DE 19813114600 DE19813114600 DE 19813114600 DE 3114600 A DE3114600 A DE 3114600A DE 3114600 C2 DE3114600 C2 DE 3114600C2
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DE
Germany
Prior art keywords
radar
rocket
data
pulse
doppler
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
DE19813114600
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German (de)
Other versions
DE3114600A1 (en
Inventor
Wolfgang Dr.-Ing. 7900 Ulm De Schaller
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Telefunken Systemtechnik AG
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Telefunken Systemtechnik AG
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Publication date
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Priority to DE19813114600 priority Critical patent/DE3114600C2/de
Publication of DE3114600A1 publication Critical patent/DE3114600A1/en
Application granted granted Critical
Publication of DE3114600C2 publication Critical patent/DE3114600C2/de
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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Classifications

    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO 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
    • G01S13/00Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88Radar or analogous systems specially adapted for specific applications
    • G01S13/89Radar or analogous systems specially adapted for specific applications for mapping or imaging
    • G01S13/90Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F42AMMUNITION; BLASTING
    • F42BEXPLOSIVE CHARGES, e.g. FOR BLASTING, FIREWORKS, AMMUNITION
    • F42B12/00Projectiles, missiles or mines characterised by the warhead, the intended effect, or the material
    • F42B12/02Projectiles, missiles or mines characterised by the warhead, the intended effect, or the material characterised by the warhead or the intended effect
    • F42B12/36Projectiles, missiles or mines characterised by the warhead, the intended effect, or the material characterised by the warhead or the intended effect for dispensing materials; for producing chemical or physical reaction; for signalling ; for transmitting information
    • F42B12/365Projectiles transmitting information to a remote location using optical or electronic means

Description

The invention relates to a method according to the preamble of claim 1 and an arrangement for performing the Procedure. Such an arrangement is for example as Interavia 5/1972, Vol. 27 (May 1972), pp. 492-493.

A number of are already available for battlefield reconnaissance Sensors available. The reconnaissance works with soaring Radar platforms on this side of the front. they has a penetration depth of 50 to 100 km (Doppler radar, Side view radar; ARGUS / lapwing, ORPHEE, SOTAS / ALARM, RF-4E / SLAR, AWACS). The target location directly over enemy territory previously used optronic sensors in platforms such as the CL-289 drone or RPVs. See. to this z. B. H. Gaertner: New systems for battlefield reconnaissance; Defense technology 4/79, p. 31.  

A sensible addition to the existing resources would be an imaging reconnaissance projectile designed by the combat batteries themselves can be fired. Experiments with such sensors based on CCD television cameras have already been made, see e.g. B. CCD: The Ultimate Shift Register; Electronic Warfare 2/79, P. 51. However, the television camera does not work for night fighting out. Thermal imaging devices can help. They also penetrate but not clouds and fog. Therefore it is fully suitable for all weather conditions only when using microwave sensors reachable. So far, however, these have suffered from inadequate Resolution. With the development of the frequency band of The active microwave image sensor moves millimeter waves in the realm of the possible. By connecting high Radar frequency with a synthetic aperture is a resolution better than TV quality possible. Such a shootable one The invention describes a sensor for the target location. It is important for weapon systems against Tanks that have a range of 10 . . 30 km high accuracy achieve by means of final phase steering.  

From the Interavia 5/1972 mentioned at the beginning is a shootable Reconnaissance missile known with a microwave pulse radar, that works on the principle of the synthetic aperture. The Radar beam sweeps over what is to be monitored in flight Glände, with the radar antenna at the tip of the missile is housed under a radome.

From the textbook by M. I. Skolnik: "Radar Handbook" (McGraw-Hill, New York, 1970), pp. 23-25 is also known to be a synthetic Operate aperture radar in squint mode, d. H. the radar beam also partially directed in the direction of flight of the missile. A Another synthetic aperture radar for site surveillance is in of US-A-41 63 231. Finally, from US-A-36 62 384 a missile rotating about its longitudinal axis with a Microwave radar for terrain surveillance described.

The object of the invention is therefore a method and an arrangement of the type mentioned at the beginning with an all-weather suitability lockable sensor for site monitoring to indicate with the the highest possible image quality can be achieved. The invention A method for solving this problem is in claim 1, the invention Arrangement described in claim 4. The further claims include advantageous developments or designs of the invention.

The invention is based on the figures and preferred embodiments explained in more detail below.  

A radar probe with an operating frequency of preferably 24 GHz is located in an artillery missile instead of the warhead. It is fired in the indirect shot by a launcher and therefore flies the target area relatively steeply from above on a ballistic path, vlg. Fig. 1. For the following estimating calculations, a path angle of 45 ° and an airspeed near the speed of sound are assumed. The radar becomes active at a height of approximately 2000 m and scans the terrain within an opening angle of 60 °. It takes 8 seconds to make contact with the ground. During this time, a complete picture is generated.

The image field is progressively scanned from the outside inwards. The rotational movement is caused by the spin of the rocket. The antenna under a radome at the tip of the rocket is deflected in its beam direction by an angle δ of 30 ° with respect to the rocket axis and has an antenna lobe of z. B. R = 7 °. Together with the swirl, a cone scan results, which draws a spiral on the ground as a result of approach, vlg. Fig. 2. A stabilized platform for the antenna is not necessary.

Since the spiral scan with the 7 ° lobe is much too coarse (400 m on the ground), a resolution grid of distance elements and Doppler zones as shown in FIG. 3, completely independent of the spiral scan, is superimposed. The two groups of standing lines, circles and ellipses, form a grid of resolution cells. At the main apexes of the ellipses, unfavorable cell shapes arise due to grinding cuts, which leads to local blurring. This effect is partially compensated towards the center by the increasing density of the Doppler zones as a result of the probe approaching the ground.

The Doppler range grating is created as a cutting line system the "Doppler cone" and distance balls with the Ground. The center of the circular cones and spheres is the Probe. The spherical shells represent the dissolution cells of the pulse radar in the radial direction accordingly the pulse width used. The cones are the geometric ones Places of constant Doppler shift.

The maximum Doppler shift due to the own motion the probe appears in the reflected signals on the Axis of the system on. The Doppler shift takes to the side from. The smallest resolvable Doppler shift defines the width of a Doppler zone. It is through the Dwell time determined during the target from the antenna lobe is swept over.

The spiral load does not generate the image, but rather only the scene lights up serially. The larger the full width at half maximum the club is, the sharper the picture paradoxically, because the Doppler resolution increases.

A special computer in a ground station takes care of the breakdown of the target information from each individual distance strip into the large number of Doppler cells, and thus into the individual pixels. The computer implements a filter bank using the algorithm of the FFT (Fast Fourier Transform) that is useful here. The image points obtained in this way are assembled and displayed from the computer to the image in the knowledge of the path parameters of the probe according to the grid, FIG. 3. The required path data can be found in the radar information of the probe.

All coherent imaging systems suffer from that "speckle" effect, after which the picture is a grainy structure  receives. With point targets one speaks of the "glint" effect. By interference from different points of the target outgoing scattered waves are irregular Erasures and reinforcements that distort the image. To remedy this, you have to waive resolution reduce the coherent integration time (Doppler cells enlarge) and an incoherent integration (without consideration the phases). This is what is shown (Amount) image overlaid several times on itself - As with conventional radar in the phosphor of the Display screen - and the speckle effect is averaged.

This incoherent integration is in the inventive Radar probe achieved in that the spiral constant is a few times smaller than the scanning lobe width. This will make the same point on the ground for multiple Circulations captured and resolved and in their intensity overlaid.

The theoretical resolution limit of a radar is given by the fact that the received backscattered energy of the resolution cell must be greater than the noise energy kT . With a limited transmission power and image build-up time, the highest possible number of cells is 1 (on the floor):

with A w = effective area of the antenna
E = transmission energy = P medium · T image
r = distance.

A minimum S / N of 1 and a "reflectivity" (m² eff / m²) of the floor of 1 were also applied, which of course does not yet reflect any practical conditions.

The optimal resolution is achieved by choosing the largest possible effective area that can be accommodated in the caliber used. The frequency of the radar and thus the focusing do not seem to matter at first. However, it does go into the optimization, namely through the shape of the resolution cells. The depth of the resolution cell is determined independently of the frequency by the pulse width of the radar. The width b is given by the Doppler shift, which can just be resolved, and is therefore sensitive to the bundling of the antenna influenced by the frequency. It applies to the system under consideration (after interim calculation)

bπϑ A w n / λ

with ϑ = 30 ° = fixed deflection of the antenna lobe against the path axis
n = number of incoherently integrated cycles (multiple coverage against speckle effect)
λ = wavelength.

Then the frequency should be chosen low.

An advantageous combination of parameters for the radar probe is the following:

This results in a smallest resolution cell of A cell = 5 m · 5 m. The figures in brackets are derived quantities. The pulse repetition frequency f p corresponds to a clear distance range corresponding to the "footprint" of the antenna lobe on the ground at the lowest occurring elevation ε min of approximately 30 ° (cf. FIG. 4). The required twist is calculated from the number of revolutions required for the image construction in relation to the image construction time (8 sec). The Doppler resolution results from the covering time of a point on the ground, according to the beam width and its speed of rotation.

With the additional assumptions of an atmospheric attenuation of L Atm 0.4 dB / km (light rain), a receiver noise figure of F = 7 dB (B = 50 MHz) and a reflectivity of R = 1 for targets and R = 0.1 for the signal to noise ratio can be calculated:

The pulse power of 10 W can be achieved with Impatt diodes. The necessary coherence of 50 Hz over 20 ms can ensured by synchronization with a Gunnoszillator will. The processor power required continues to increase estimated below. According to the current status the circuit technology are provided as well as the Power of the microwave components.

The echo signals from the radar probe only form an image after transformation. The digital signal processing required for this is divided into the preprocessing in the probe with an arrangement according to FIG. 5, and the image calculation on the ground with an arrangement according to FIG. 6. The purpose of the preprocessing is to reduce the data rate transmitted by radio.

The radar probe contains the three modules radar head, signal preprocessing and radio data transmitter, cf. Fig. 5. The radar head consists of the parabolic antenna A (approx. 150 mm ⌀) under a radome and the radar transceiver with an Impatt diode pulse source Impatt, a push-pull mixer GM , an IF amplifier ZF and a quadrature mixer stage QM . The two output signals I and Q of the radar head are digitized with 6 bits and 75 MHz. The complex video signal obtained in this way is digitally processed further in the probe in order to reduce redundancy.

The redundancy of the raw video signal lies in the fact that it contains the Doppler spectrum from zero to the pulse repetition frequency f p = 150 kHz, of which only a small part is occupied due to the limited angular range of the antenna lobe. The Doppler shift f D at the placement angle ϑ is:

The half-width of the antenna covers the range ϑ - R / 2 to ϑ + R / 2. With the above-mentioned parameters of the radar probe one obtains at the range limits

f D (30 ° + 3.5 °) = 46.7 kHz

f D (30 ° - 3.5 °) = 50.1 kHz.

The information is therefore in a bandwidth of 3.4 kHz included, corresponding to 2.3% of that from the radar with its "Sampling frequency" of 150 kHz total width. Taking into account the finite steepness of the edges of the diagram the antenna becomes a Doppler transmission bandwidth selected from 5 kHz. This will result in data reduction achieved by 30: 1.

In order not to fold the receiver noise outside the occupied part of the Doppler band into the useful signal by undersampling at 5 kHz, prior digital bandpass filtering is necessary. The center frequency depends on the speed of the probe and can therefore vary. It is therefore advantageous to choose a combination of mixing stage M , Doppler estimator (middle Doppler), and low-pass filter TP , as shown in FIG. 5, instead of an adaptive bandpass. In the mixer stage, the signal is mixed with the average Doppler frequency that was previously determined from the signal. The low-pass filter has a bandwidth of ± 2.5 kHz. Because of the complex signal display, the entire Doppler band of 5 kHz width can be clearly recorded with this band limitation.

After the low-pass filter TP , the signal in the individual distance elements need only be sampled at 5 kHz. Since all the stages of signal processing described here are multiplex systems that perform the operations channel-by-channel on a bundle of 500 distance channels (75 MHz: 150 kHz), the channel-side sampling at 5 kHz means the following: At intervals of 0.2 ms, bundles fall out of 500 complex samples with a clock of 75 MHz. This intermittent data accumulation can be smoothed with a buffer memory SP and thus converted into a continuous data stream of 2.5 · 10⁶ complex values per second. The real part and the imaginary part can each be represented with about 8 bits, so that the radio link to the ground station has to manage 40 Mbit / s.

The following redundancy is still present in this transmission rate contain:

Factor 4 oversampling against "speckle"
Factor 2 unused phase information of the pixels
Factor 1.5 oversampling at a distance
Factor 1.5 oversampling in Doppler
Factor approx. 2 redundant PRF due to ε ≠ const.
Factor 2 redundant image construction with spiral scanning

A total of 60. . . 80x redundancy can only be achieved by the image calculation can be eliminated (image information approx. 3 Mbit in 8 sec). As long as this for reasons of effort  cannot be carried out in the probe yet the radio channel with the excessive data rate of 40 Mbit / s be charged. For comparison: the data rate for digital Transmission of television is 100 Mbit / s.

The data link for transmission can always be there maximum visual line of sight to the probe 30 km distance with a microwave frequency between 10 and 20 GHz are operated. Measures to protect against Jammers must be seized. Because the transferred Signal has a lot of redundancy right from the start it's not that sensitive to interference.

The ground station, FIG. 6, contains, in addition to a radio data receiver E, a special computer as an image processor and a screen device for display. The image resolution of the radar requires approximately 1000 lines to be displayed. The components of the ground station and their mode of operation are known in principle to those skilled in the art from radar signal processing. It is therefore only briefly discussed in the following. The main modules for image acquisition shown by boxes in FIG. 6 can be implemented in software. The position parameters of the probe, such as the path angle, the rotation phase of the Antelle, the distance to the ground and the speed required for image generation, can be found in the radar signal (module image synchronization).

Before the fine structure of the image can be calculated by Fourier transformation with the FFT algorithm, the "migration" of the ground-mounted resolution cells typical of synthetic aperture radars must be compensated for by the probe-fixed resolution grid. The slight migration movement (range migration, Doppler defocusing) arises from the movement of the probe during the short recording time T koh of a ground point. This is compensated for by interpolation over several distance elements in the block formation for the Fourier transformation, as well as by targeted phase correction of the block with a chirp function.

The Fourier transformation represents the main expenditure of the image calculation. The blocks to be transformed contain approx. 100 relevant points per distance element. The number results from the PRF pre-filtered to 5 kHz in the probe and the illumination duration T koh = 20 ms. These points are therefore samples from a short strip on the ground with r = const. , The individual sub-cells of which are contained in the form of Doppler vibrations of different frequencies in the signal mixture which is 100 samples long. Since the antenna lobe and therefore the duration of the illumination are not sharply limited, the block with N ≈ 200 must be selected to be somewhat larger. The transformation effort for this is

N Mult. = 2 N 1 dN ≅ 3 · 10³

real multiplications (8 × 8 bits) per block of 20 ms. Since 500 distance cells are distinguished, 500 such blocks have to be transformed in 20 ms under real-time conditions. From this follows the multiplication rate for the FFT

N Mult = 500 · 3 · 10³ / 20 ms ≈ 10⁸ / s.

This figure, rounded up slightly, can also be seen as a guideline for the overall processor performance due to the overweight of the FFT in the image calculation.

The multiplication performance is based on today's State of the circuit technology with approx. 10 multiplier circuits to be provided along with peripherals (hardwired Processor). A pure software solution in one Standard process computers will not be possible in the foreseeable future. With an array processor, the required Performance in the range given the short word length of the (future) possible.

Claims (8)

1. A method for terrain monitoring with a lockable sensor in the form of a microwave pulse radar housed in a rocket, the radar antenna of which is deflected under a radome at the tip of the rocket in its beam direction by a fixed angle ϑ with respect to the rocket axis, in which method the resolution of the Radar is increased according to the principle of the synthetic aperture, the aperture being given in each case by the distance flown through during a coherent evaluation interval, characterized by the following features:
  • - The rocket is fired in an indirect shot and flies steeply to the area to be monitored from above. The pulse radar becomes active from a defined height ( FIG. 1).
  • - The missile receives a twist, so that the radar lobe spirals over the area to be monitored sweeps from outside to inside and scans ( Fig. 2). Through a suitable choice of the spin of the rocket, each point of the resolution grid is covered several times and the corresponding data is overlaid in the ground station.
  • - The reflected radar pulses are received in the rocket and pre-processed into a data sequence. The rocket transmits the data sequence to a ground station by radio.
  • - The data sequence is transformed in the ground station and built into an image. A resolution grid of distance elements and Doppler zones is used as a basis ( Fig. 3). The position parameters of the rocket required for this are taken from the data sequence.
2. The method according to claim 1, characterized in that the pulse radar works in the millimeter wave range.
3. The method according to claim 1, characterized in that to transmit the data sequence from the rocket to the ground station a frequency between 10 and 30 GHz is used.
4. Arrangement for performing the method according to one of the preceding claims, characterized by the following features:
  • - A missile contains a radar head, a device for preprocessing data, and a radio data transmitter (S). The radar head consists of a parabolic antenna (A) under a radome, with a fixed deflection angle ϑ between the beam direction and the missile axis, a radar transceiver with a pulse source (Impatt) , a push-pull mixer (GM) , an IF amplifier (ZF) and a quadrature mixer (QM) . The device for preprocessing data consists of two analog / digital converters (A / D), a digital band limiter (middle Doppler, TP) , and a buffer memory (SP) .
  • - A ground station contains a data receiver (E) , a special computer, and a screen. The special computer has modules for determining the position parameters of the rocket (image synchronization), for compensating for the migration movement of the resolution grid (compensation), which is caused by the movement of the rocket, for filtering (FFT) the data and for image construction ( FIGS. 5 and 6 ).
5. Arrangement according to claim 4, characterized in that the parabolic antenna (A) has a diameter of about 100. . . 200 mm has that the antenna lobe is about 7 °, and that the deflection angle ϑ is about 30 °.
6. Arrangement according to claim 5, characterized in that the radar transceiver with a pulse power of about 10 W, a pulse width of about 20 nsec and one Pulse repetition frequency of about 150 kHz works.
7. Arrangement according to claim 4, characterized in that the pulse frequency (Impatt) is constructed from Impatt diodes which are synchronized by means of a Gunn oscillator.
8. The arrangement according to claim 4, characterized in that the digital band limiter consists of a mixing stage and a low-pass filter (TP) , and that in the mixing stage, the mean Doppler frequency (mean. Doppler) is determined and thus the incoming data are mixed (M) ( Fig. 5).
DE19813114600 1981-04-10 1981-04-10 Expired - Fee Related DE3114600C2 (en)

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DE3114600C2 true DE3114600C2 (en) 1990-06-21

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7196653B2 (en) 2003-05-21 2007-03-27 Astrium Limited Imaging apparatus and method
CN103675760A (en) * 2013-12-03 2014-03-26 北京理工大学 Satellite-borne geosynchronous orbit synthetic aperture radar posture guiding method

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3313648C2 (en) * 1983-04-15 1987-08-27 Diehl Gmbh & Co, 8500 Nuernberg, De
DE3430888C2 (en) * 1984-08-22 1988-10-06 Messerschmitt-Boelkow-Blohm Gmbh, 8012 Ottobrunn, De
GB2252207B (en) * 1985-03-19 1992-12-16 British Aerospace Integrated antenna/mixer devices and weapon guidance systems
US5052045A (en) * 1988-08-29 1991-09-24 Raytheon Company Confirmed boundary pattern matching
EP0455864A3 (en) * 1990-05-09 1992-08-26 Messerschmitt-Boelkow-Blohm Gmbh Projectile for ground observation

Family Cites Families (2)

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Publication number Priority date Publication date Assignee Title
US3662384A (en) * 1957-03-13 1972-05-09 Martin Marietta Corp Doppler mapping radar
US4162231A (en) * 1977-12-28 1979-07-24 The United States Of America As Represented By The United States Department Of Energy Method for recovering palladium and technetium values from nuclear fuel reprocessing waste solutions

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7196653B2 (en) 2003-05-21 2007-03-27 Astrium Limited Imaging apparatus and method
CN103675760A (en) * 2013-12-03 2014-03-26 北京理工大学 Satellite-borne geosynchronous orbit synthetic aperture radar posture guiding method
CN103675760B (en) * 2013-12-03 2015-12-02 北京理工大学 A kind of spaceborne geostationary orbit synthetic-aperture radar attitude guidance method

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