CA1320752C - Moving target indication unit - Google Patents
Moving target indication unitInfo
- Publication number
- CA1320752C CA1320752C CA000587380A CA587380A CA1320752C CA 1320752 C CA1320752 C CA 1320752C CA 000587380 A CA000587380 A CA 000587380A CA 587380 A CA587380 A CA 587380A CA 1320752 C CA1320752 C CA 1320752C
- Authority
- CA
- Canada
- Prior art keywords
- parameters
- unit
- moving target
- target indication
- clutter
- 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 - Lifetime
Links
- 238000001514 detection method Methods 0.000 claims abstract description 9
- 238000002592 echocardiography Methods 0.000 claims description 6
- 230000001629 suppression Effects 0.000 description 6
- 238000000034 method Methods 0.000 description 3
- 101100269836 Mus musculus Ank1 gene Proteins 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- RXQCGGRTAILOIN-UHFFFAOYSA-N mephentermine Chemical compound CNC(C)(C)CC1=CC=CC=C1 RXQCGGRTAILOIN-UHFFFAOYSA-N 0.000 description 1
- 229960002342 mephentermine Drugs 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
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
- G01S13/00—Systems 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
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S13/06—Systems determining position data of a target
- G01S13/08—Systems for measuring distance only
- G01S13/10—Systems for measuring distance only using transmission of interrupted, pulse modulated waves
- G01S13/22—Systems for measuring distance only using transmission of interrupted, pulse modulated waves using irregular pulse repetition frequency
- G01S13/227—Systems for measuring distance only using transmission of interrupted, pulse modulated waves using irregular pulse repetition frequency with repetitive trains of uniform pulse sequences, each sequence having a different pulse repetition frequency
-
- 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
- G01S13/00—Systems 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
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S13/50—Systems of measurement based on relative movement of target
- G01S13/52—Discriminating between fixed and moving objects or between objects moving at different speeds
- G01S13/522—Discriminating between fixed and moving objects or between objects moving at different speeds using transmissions of interrupted pulse modulated waves
- G01S13/524—Discriminating between fixed and moving objects or between objects moving at different speeds using transmissions of interrupted pulse modulated waves based upon the phase or frequency shift resulting from movement of objects, with reference to the transmitted signals, e.g. coherent MTi
- G01S13/5244—Adaptive clutter cancellation
Abstract
Abstract Moving target indication unit provided with a doppler filter bank (1) with n output channels Ai (i = 0, 1, 2, ..., n-1), several threshold circuits (24.i) connected to the output channels, a detection and registration unit (7, 14, 18, 23) provided with means (7, 14, 18) for the determination and registration, per azimuth cell, of a parameter for the amount: of clutter in an azimuth cell.
The said means are further suitable for determining, based on the output signals of the filter bank (1), k (k ? 2) parameters per azimuth cell and processing per azimuth cell the combination of k parameters to obtain n threshold values, used to set the n threshold circuits.
The said means are further suitable for determining, based on the output signals of the filter bank (1), k (k ? 2) parameters per azimuth cell and processing per azimuth cell the combination of k parameters to obtain n threshold values, used to set the n threshold circuits.
Description
1 ~20752 Moving target indication unit The present invention relates to a moving target indication unit provided ~ith a bank of Doppler fil.ters ~ith n output channels Ai (i = 0, 1, 2, ..., n-l), several threshold circuits connected to the output channels, a detection and registration unit provided with means for the determination and reL;istration, per azimuth cell, of a parameter for the amount of clutter in an azimuth cell, and for setting the threshold circuits per azimuth cell on the basis of the registered parametsr.
In such a known system, the output signal of filter channel 0, the channel with Doppler speeds of around 0 Hz, is used to estimate a parameter of the amount of clutter in an azimuth cell. This value is subsequently registered in a memory. To obtain a parameter for the amount of clutter in the remaining filter channels, a fixed functional connection is assumed between, on ths one hand, the amount of clutter in output channel 0 and, on the other hand, the amount of clutter in the remaining channels. In other words, a distribution of ~he clutter across the different channels is assumed. This implies that an estimation is made of the amount of clutter in the filter channels Ai (i = 1, 2, ..., n-l). It has been proven in practice that clutter suppression is noe always effective.
The inventor found that this is caused by the fact that the clutter distribution across the differsnt output channels Ai is dependent on the type of clutter confronted. Diff~rent types of clut~er occur especially in the case of search radars, where the radar covers different types of territories, e.g. land and sea clutter. Difierent types of clutter also occur as a result of variable weather conditions (anaprop).
The invention has for its object to solve the above-mentioned problems on the basis of the conclusion that the unsatisfactory 1 3~0752 clutter suppression is caused by a variable distribution of the amount of clutter across the different output channels Ai and consists in that the means mentioned are suitable for determining, based on the output signals of the filterbank, k ~k ~ 2) parameters per azimuth cell and processing per azimuth cell the combination of k parameters to ob1;ain n threshold values, used to set the n threshold circuits.
More particularly, the present invention provides moving target indication unit comprising: a. a doppler filter bank having n output channels Ai (i = , l, 2, ..., n-l), said fi.lter bank producing on said channels output signals derived from echoes returned from a plurality of azimuth cells; b. a detec-tion and registration unit electrically connected to the output channels and including means for determining and storing from the signals produced on k of said n output channels, for each of the azimuth cells, k respective parameters representative of the amount of clutter in said cells, where k 2 2, and for produc:ing threshold values from the parameters, said unit further including interpolation means for processing at least certain ones of k parameters to determine at least one interpolated threshold value;
and c. a plurality of threshold circuits electrically connected to the output channels and to the detection and registration unit, threshold levels of said circuits being set for said azimuth cells by respective one of said threshold values and interpolated threshold values.
Because, according to the invention, for k filter channels Ai with k 2 2 the amount of clutter is determined, it is possible to obtain a be~tter impression of the changlng functional relationships as regards the distribution of the amount of clutter across various output channels. To determine the k parameters bi belonging to the k filter channels Ai concerned, a parallel circuit of k known clutter analysis units can be used.
A special embodiment of the MTI-unit according to the invention is characterised in that k = n.
Because for each filter channel the amount of clutter per azimuth cell is determined, the threshold circuit belonging to .i~ 2 the filter channel can be optimally adjusted without assuming a functional relationship indicating the distribution of clutter across the various filter channels.
An advantageous embodiment of the MTI-unit according to the invention is characterised in that the means for determination and registration of the parameters bi and bi~2 based on the output signals Ui and Ui~2 of output channels Ai and Ai~2, for obtaining threshold values Bi and Bi+2 based on the said parameters bi and bi~2 and for obtaining threshold ~alues Bi from parameters bi and bi~2 by means of interpolation.
il~, . r r~ \, 2a Due to the application of interpolation, the memory capacity of the MTI unit can be limited to allow a chsaper constructlon of the MTI unit. It has besn proven, that assuming a properly chosen form of interpolstion, the performance is only slightly deteriorated, ~n especially effective MTI unit can be applied in a radar apparatus with p different p.r.f.'s, where the means m~ntioned are suitable for determination and registration of the said parameters per azimuth cell and per p.r.f., and for setting the sald threshold circuits per azimuth cell and per p.r.f. used.
By means of the interpolation methods described above, however, the number of clutter maps can be reduced. The combination of staggering on the one hand and interpolation on the other hand shows a combined result, allowing a particularly effective clutter supprassion, while multiple-time-around echoes can be suppressed.
The invention will be further explained with reference to the following figures, of ~hich 0 Fig. 1 sho~s a first possible embodiment of an ~TI unit ac~ording to the invention;
Fig. 2 shows a division of the range of a radar apparatus into azlmuth cells;
Fig. 3 shows a first embodimsnt of the clutter analysls unit of Fig. l;
Fi8. 4 shows an embodiment of the log-modulus unit operating on a time-shar~ng basis and the clutter analysis unit of fig. l;
Fig. 5 shows a cost-effective embodiment of an NTI unit accordin~ to the invention.
Fig. 1 illustra~es a doppler filter bank 1 wlth 16 output channels Ai (i ~ 0, 1, ..., 15) (n - 16).
1 3207 5~
Tha output signsls of filter bank 1 in thls embodiment consist in echo signals from a pulse doppler surveillance radar. These echo signsls have after reception been transformed to an intermediate frequency. The dopplar frequencias of the echo signals transformed to intermediate frequency are analysed in frequency by rneans of doppler filter ~ank 1. In practice, it is possibla that the echo signals, before being supplied to the doppler ~ilter, are digitised by means of an A/D converter, snabling the appllcation of a 16-point FFT for the doppler filter bank. ~owever, this does not axclude application of an analogue 16-point doppler filter.
Filter channel Ao embodies a zero-velocity filter. The sixteen output signals Ui (i ~ 0, 1, ..., 15) of the doppler filter bank are supplied via lines 2.i (i = 0, 1, ..., 15) respectively to log-modulus units 3.i (i ~ 0, 1, ..., 15). It is also possible to implement units 3.i for generation of the modulus square or the modulus of ths input signal. The area covered by the search radar is illustrated in fig. 2. The area has been divided into a number of azimuth cells, one of which is azlmuth cell 4.
For the embodlment in question it is assumed that the pulse repetition frequency of the search radar apparatus lnto which the ~TI-unit has been implemented is 400 Hz, while a complete revolution is made in 6 sec. The radar apparatus therefore generates 2400 transmitter pulses in one revolution. The 16-point FFT sweeps are executed with a mutual overlap of twelve radar sweeps, i.e. two subsequent FFT sweeps covPr an azimuth angle corresponding wlth the azimuth angle covered by four transmitter pulses. However, one azimuth cell covers 1.4 (one revolution comprises 256 azimuth cells), so ona azimuth cell comprises two or three FFT sweeps.
For each azimuth cell the frequency spectrum is determined by means o~ doppler filterbank 1. Output signals U~ 0, 1, .,., 15) of the log-modulus units 3.i (i = 0, ..., 15) belonging to an azimuth ~ 320752 cell, are supplied via lines 5.i and 6.i (i ~ 0, ..., 15) to a clutter analysis unit 7. Clutter analysis unit 7 determines per cell for each ou~put channel Ai A parameter bl (i D 0, 1, ..., 15) representing the maximum amount of clutter.
Fig. 3 illustrates a possible embo<llment of clutter analysis unlt 7.
The cluttsr analysis unit consists of sixteen parallel-connected and identical maximum detectors B.i (i = 0, ..., 15). A maximum detector 8.i is provided with a comparator 9.i and a register lO.i. At the start of each azimuth cell register lO.i is reset to ~ero. Signal Ul' belonging to an azimuth cell is supplied to comparator 9.i via line 6.i. Comparator 9.i also receives the parameter bi, already stored in register lO.i, via line ll.i. If Ui' 2 bi, the comparator switches a switching unit 12.i to position I, causing bi to be overwritten with the value of Ui'. In case Ui' ~ bi, comparator 9.i sets switching unit 12.i to position II, causing the original value of bi to be written into regis~er lO.i again. In this way, the maximum value of U'imax ~ bi is selected from the subsequent signals Ui belonging to the subsequent FFT sweeps of one azimuth cell.
The sixteen parameters bi are supplied to a filter unit 14 via lines 13.i (i = 0, ..., 15) for each azimuth cell. For the filter unit, madlan, mean or top(modulus) filters may be applied.
For mean filters, linear filters qualify, such as low-pass filters, FI~ filters or recursive filters. A top filter determines the maximum value of a frequency distribution. In this case the use of low-pass filters is further described. Low-pass unit 14 is in thls configuration provided with sixtean parallel-connscted and identical low-pass filters 15.1 (i ~ 0, ..., 15). The sixteen output cignals of low-pass unit 14 are stored in a memory 18 via lines 17.i (i - 0, ... , 15). Low-pass unit 14 also receives, via lines 16.i ti = 0, ... , 15), the parameters bi of an azimuth cell already stored in memory 18. The transfer of a low-pass filter 15.i can be described as follows:
i~ io ~ o), ~here 0 < ~ < 1.
In this formula, bi is the old parameter bi, obtained during a o preceding revolution, stored in the memory and supplied via llne 16.i, bi is a parameter of an azimuth cell determined by clutter analysis unit 7 and supplied via line 13.1, and bi is the parameter supplied via line 17.i with which the parameter bi is overwritten in the memory.
It will be clear that it is possible to replace on a time-sharing basis the clutter analysis unit and the log-modulus units 3.i with one comparator 9.i, register lO.i and a log~modulus unit 3.i (see Fig. 4). For this purpose, two switching means 20 and 21 are implemented which ensure that signals bi (~ ..-, 15) are processPd and supplied by successively assuming positions 0 to 15.
Thus the amount of clutter is recorded for each cell. In this way, a recording is made, as it were, o sixteen clutter maps of the are~
covered by the search radar: one clutter map for each output channel of the doppler filter. ~hen the search radar covars an azimuth cell of the environment, the accompanying parameters bi (hereafter called bi) are read from the memory and supplied to a threshold value unit 23 via lines 22.i (i = 0, ..., 15). Threshold value unit 23 for each parameter bi generates an accompanying signal Bi ~i = 0, ..., 15), which is used to set the threshold level of the sixteen threshold circuits 24.i (i = 0, ..., 15) respectively via lines 25.i ~i - 0, ..., 15). The output signals Ui' of the log-modulus unit 3.i are supplied to threshold circuit 2~.i via lin~s 5.i (i = 0, ..., 15). I output signals Ai of a log-modulus unit 3.i exceed the accompanying threshold value Bi, this signal is supplied for further processing via the accompanying threshold circuits 24.i to lines 26.i (1 = 0, ..., 15). ~ecause for each output signal the accompanying clutter map is recorded in the memor~, optimal clutter suppression is realised.
An especially cost-effective embodiment is illustrated in Fig. 5.
In this embodiment, only the eight output signals Ui' of log-modulus units 3.i (i = 0, 2, 4, ..., 14) are supplied to clutter analysis unit 7. Eight clutter maps are ther.efore ~tored in the memory, belonging to the output signals of logmodulus units 3.1 ~i ~ 0, 2, 4, ..., 14). When the radar apparat:us covers an azimuth cell of Fig. 2, the eight accompanying parameters bi ti = 0, 2, 4, ... , 14) are supplied to threshold value unit 23 via lines 22.i (i = 0, 2, ~, ..., 14). Threshold value unit 23 generates eight threshold value signals Bi (i - 0, 2, ..., 14) from parameters bi (i ~ 0, 2, ....
14).
i5 Threshold valuas Bi (i = 1, 3, ..., 15) ars obtained through interpolation. For this purpose, threshold valua unlt 23 is provided with means for the execution of the following calculation:
bi+l ~ 2, whare i = 0, 2, ................ , 14, where bl6 = bo~
From the values bi (i ~ 1, 3, ..., 15) obtained through inter-polation, threshold value unit 23 generates threshold value signals Bi (i ~ 1, 3~ ..., 15), whlch are supplied to thr~shold circuits 24.i (i ~ 1, 3, ..., 15) via lines 25.i (i = 1, 3, ..., 15) respectively.
The MTI uni~ is provided with a timing generator 27 for generating signals S to control the MTI unit in ~ime.
It will be clear that according to the invention other interpolation methods can be. used as wall. It is also possible to further reduce the number of cluttar maps. Thus, it has been shown that an especially effective clutter suppression is or.ly obtained if rlutter maps are compiled for output chann,els Ai (i ~ 0, 2, 4, 8, 12, 14).
For output channels Ai (i ~ 6, 7, 9, 10), the threshold unit uses the clutter map belonging to outpue channel A8, while for the other channels Ai (i = 1, 3, 5, 11, 13, l5), the abo~e-described ~nterpolation between two neighbou:ring output channels is applied.
If the radar apparatus in which the above-described MTI unit is applied, uses a staggered pulse repetition fxequency (two or more p.r.f.'s), it is possible to record a set of clutter maps as described above for the pulse repetition frequencies. The number of clutter maps will then double in case staggering implies the use of two p.r.f.'s. Staggering is important for the suppression of multiple-time-around echoes, because they take up different positions for the different p.r.f.'s. If for staggering p different p.r.f.'s are used, the number of clutter maps will be increased by a factor p.
By means of the above-described interpolation methods, the number of clutter maps can however ba decreased again. The combination of staggering on the one hand and interpolation on the other hand has the combined result of allowing a specially effect~ve clut~er suppression while suppressing multiple-time-axound echoes.
In such a known system, the output signal of filter channel 0, the channel with Doppler speeds of around 0 Hz, is used to estimate a parameter of the amount of clutter in an azimuth cell. This value is subsequently registered in a memory. To obtain a parameter for the amount of clutter in the remaining filter channels, a fixed functional connection is assumed between, on ths one hand, the amount of clutter in output channel 0 and, on the other hand, the amount of clutter in the remaining channels. In other words, a distribution of ~he clutter across the different channels is assumed. This implies that an estimation is made of the amount of clutter in the filter channels Ai (i = 1, 2, ..., n-l). It has been proven in practice that clutter suppression is noe always effective.
The inventor found that this is caused by the fact that the clutter distribution across the differsnt output channels Ai is dependent on the type of clutter confronted. Diff~rent types of clut~er occur especially in the case of search radars, where the radar covers different types of territories, e.g. land and sea clutter. Difierent types of clutter also occur as a result of variable weather conditions (anaprop).
The invention has for its object to solve the above-mentioned problems on the basis of the conclusion that the unsatisfactory 1 3~0752 clutter suppression is caused by a variable distribution of the amount of clutter across the different output channels Ai and consists in that the means mentioned are suitable for determining, based on the output signals of the filterbank, k ~k ~ 2) parameters per azimuth cell and processing per azimuth cell the combination of k parameters to ob1;ain n threshold values, used to set the n threshold circuits.
More particularly, the present invention provides moving target indication unit comprising: a. a doppler filter bank having n output channels Ai (i = , l, 2, ..., n-l), said fi.lter bank producing on said channels output signals derived from echoes returned from a plurality of azimuth cells; b. a detec-tion and registration unit electrically connected to the output channels and including means for determining and storing from the signals produced on k of said n output channels, for each of the azimuth cells, k respective parameters representative of the amount of clutter in said cells, where k 2 2, and for produc:ing threshold values from the parameters, said unit further including interpolation means for processing at least certain ones of k parameters to determine at least one interpolated threshold value;
and c. a plurality of threshold circuits electrically connected to the output channels and to the detection and registration unit, threshold levels of said circuits being set for said azimuth cells by respective one of said threshold values and interpolated threshold values.
Because, according to the invention, for k filter channels Ai with k 2 2 the amount of clutter is determined, it is possible to obtain a be~tter impression of the changlng functional relationships as regards the distribution of the amount of clutter across various output channels. To determine the k parameters bi belonging to the k filter channels Ai concerned, a parallel circuit of k known clutter analysis units can be used.
A special embodiment of the MTI-unit according to the invention is characterised in that k = n.
Because for each filter channel the amount of clutter per azimuth cell is determined, the threshold circuit belonging to .i~ 2 the filter channel can be optimally adjusted without assuming a functional relationship indicating the distribution of clutter across the various filter channels.
An advantageous embodiment of the MTI-unit according to the invention is characterised in that the means for determination and registration of the parameters bi and bi~2 based on the output signals Ui and Ui~2 of output channels Ai and Ai~2, for obtaining threshold values Bi and Bi+2 based on the said parameters bi and bi~2 and for obtaining threshold ~alues Bi from parameters bi and bi~2 by means of interpolation.
il~, . r r~ \, 2a Due to the application of interpolation, the memory capacity of the MTI unit can be limited to allow a chsaper constructlon of the MTI unit. It has besn proven, that assuming a properly chosen form of interpolstion, the performance is only slightly deteriorated, ~n especially effective MTI unit can be applied in a radar apparatus with p different p.r.f.'s, where the means m~ntioned are suitable for determination and registration of the said parameters per azimuth cell and per p.r.f., and for setting the sald threshold circuits per azimuth cell and per p.r.f. used.
By means of the interpolation methods described above, however, the number of clutter maps can be reduced. The combination of staggering on the one hand and interpolation on the other hand shows a combined result, allowing a particularly effective clutter supprassion, while multiple-time-around echoes can be suppressed.
The invention will be further explained with reference to the following figures, of ~hich 0 Fig. 1 sho~s a first possible embodiment of an ~TI unit ac~ording to the invention;
Fig. 2 shows a division of the range of a radar apparatus into azlmuth cells;
Fig. 3 shows a first embodimsnt of the clutter analysls unit of Fig. l;
Fi8. 4 shows an embodiment of the log-modulus unit operating on a time-shar~ng basis and the clutter analysis unit of fig. l;
Fig. 5 shows a cost-effective embodiment of an NTI unit accordin~ to the invention.
Fig. 1 illustra~es a doppler filter bank 1 wlth 16 output channels Ai (i ~ 0, 1, ..., 15) (n - 16).
1 3207 5~
Tha output signsls of filter bank 1 in thls embodiment consist in echo signals from a pulse doppler surveillance radar. These echo signsls have after reception been transformed to an intermediate frequency. The dopplar frequencias of the echo signals transformed to intermediate frequency are analysed in frequency by rneans of doppler filter ~ank 1. In practice, it is possibla that the echo signals, before being supplied to the doppler ~ilter, are digitised by means of an A/D converter, snabling the appllcation of a 16-point FFT for the doppler filter bank. ~owever, this does not axclude application of an analogue 16-point doppler filter.
Filter channel Ao embodies a zero-velocity filter. The sixteen output signals Ui (i ~ 0, 1, ..., 15) of the doppler filter bank are supplied via lines 2.i (i = 0, 1, ..., 15) respectively to log-modulus units 3.i (i ~ 0, 1, ..., 15). It is also possible to implement units 3.i for generation of the modulus square or the modulus of ths input signal. The area covered by the search radar is illustrated in fig. 2. The area has been divided into a number of azimuth cells, one of which is azlmuth cell 4.
For the embodlment in question it is assumed that the pulse repetition frequency of the search radar apparatus lnto which the ~TI-unit has been implemented is 400 Hz, while a complete revolution is made in 6 sec. The radar apparatus therefore generates 2400 transmitter pulses in one revolution. The 16-point FFT sweeps are executed with a mutual overlap of twelve radar sweeps, i.e. two subsequent FFT sweeps covPr an azimuth angle corresponding wlth the azimuth angle covered by four transmitter pulses. However, one azimuth cell covers 1.4 (one revolution comprises 256 azimuth cells), so ona azimuth cell comprises two or three FFT sweeps.
For each azimuth cell the frequency spectrum is determined by means o~ doppler filterbank 1. Output signals U~ 0, 1, .,., 15) of the log-modulus units 3.i (i = 0, ..., 15) belonging to an azimuth ~ 320752 cell, are supplied via lines 5.i and 6.i (i ~ 0, ..., 15) to a clutter analysis unit 7. Clutter analysis unit 7 determines per cell for each ou~put channel Ai A parameter bl (i D 0, 1, ..., 15) representing the maximum amount of clutter.
Fig. 3 illustrates a possible embo<llment of clutter analysis unlt 7.
The cluttsr analysis unit consists of sixteen parallel-connected and identical maximum detectors B.i (i = 0, ..., 15). A maximum detector 8.i is provided with a comparator 9.i and a register lO.i. At the start of each azimuth cell register lO.i is reset to ~ero. Signal Ul' belonging to an azimuth cell is supplied to comparator 9.i via line 6.i. Comparator 9.i also receives the parameter bi, already stored in register lO.i, via line ll.i. If Ui' 2 bi, the comparator switches a switching unit 12.i to position I, causing bi to be overwritten with the value of Ui'. In case Ui' ~ bi, comparator 9.i sets switching unit 12.i to position II, causing the original value of bi to be written into regis~er lO.i again. In this way, the maximum value of U'imax ~ bi is selected from the subsequent signals Ui belonging to the subsequent FFT sweeps of one azimuth cell.
The sixteen parameters bi are supplied to a filter unit 14 via lines 13.i (i = 0, ..., 15) for each azimuth cell. For the filter unit, madlan, mean or top(modulus) filters may be applied.
For mean filters, linear filters qualify, such as low-pass filters, FI~ filters or recursive filters. A top filter determines the maximum value of a frequency distribution. In this case the use of low-pass filters is further described. Low-pass unit 14 is in thls configuration provided with sixtean parallel-connscted and identical low-pass filters 15.1 (i ~ 0, ..., 15). The sixteen output cignals of low-pass unit 14 are stored in a memory 18 via lines 17.i (i - 0, ... , 15). Low-pass unit 14 also receives, via lines 16.i ti = 0, ... , 15), the parameters bi of an azimuth cell already stored in memory 18. The transfer of a low-pass filter 15.i can be described as follows:
i~ io ~ o), ~here 0 < ~ < 1.
In this formula, bi is the old parameter bi, obtained during a o preceding revolution, stored in the memory and supplied via llne 16.i, bi is a parameter of an azimuth cell determined by clutter analysis unit 7 and supplied via line 13.1, and bi is the parameter supplied via line 17.i with which the parameter bi is overwritten in the memory.
It will be clear that it is possible to replace on a time-sharing basis the clutter analysis unit and the log-modulus units 3.i with one comparator 9.i, register lO.i and a log~modulus unit 3.i (see Fig. 4). For this purpose, two switching means 20 and 21 are implemented which ensure that signals bi (~ ..-, 15) are processPd and supplied by successively assuming positions 0 to 15.
Thus the amount of clutter is recorded for each cell. In this way, a recording is made, as it were, o sixteen clutter maps of the are~
covered by the search radar: one clutter map for each output channel of the doppler filter. ~hen the search radar covars an azimuth cell of the environment, the accompanying parameters bi (hereafter called bi) are read from the memory and supplied to a threshold value unit 23 via lines 22.i (i = 0, ..., 15). Threshold value unit 23 for each parameter bi generates an accompanying signal Bi ~i = 0, ..., 15), which is used to set the threshold level of the sixteen threshold circuits 24.i (i = 0, ..., 15) respectively via lines 25.i ~i - 0, ..., 15). The output signals Ui' of the log-modulus unit 3.i are supplied to threshold circuit 2~.i via lin~s 5.i (i = 0, ..., 15). I output signals Ai of a log-modulus unit 3.i exceed the accompanying threshold value Bi, this signal is supplied for further processing via the accompanying threshold circuits 24.i to lines 26.i (1 = 0, ..., 15). ~ecause for each output signal the accompanying clutter map is recorded in the memor~, optimal clutter suppression is realised.
An especially cost-effective embodiment is illustrated in Fig. 5.
In this embodiment, only the eight output signals Ui' of log-modulus units 3.i (i = 0, 2, 4, ..., 14) are supplied to clutter analysis unit 7. Eight clutter maps are ther.efore ~tored in the memory, belonging to the output signals of logmodulus units 3.1 ~i ~ 0, 2, 4, ..., 14). When the radar apparat:us covers an azimuth cell of Fig. 2, the eight accompanying parameters bi ti = 0, 2, 4, ... , 14) are supplied to threshold value unit 23 via lines 22.i (i = 0, 2, ~, ..., 14). Threshold value unit 23 generates eight threshold value signals Bi (i - 0, 2, ..., 14) from parameters bi (i ~ 0, 2, ....
14).
i5 Threshold valuas Bi (i = 1, 3, ..., 15) ars obtained through interpolation. For this purpose, threshold valua unlt 23 is provided with means for the execution of the following calculation:
bi+l ~ 2, whare i = 0, 2, ................ , 14, where bl6 = bo~
From the values bi (i ~ 1, 3, ..., 15) obtained through inter-polation, threshold value unit 23 generates threshold value signals Bi (i ~ 1, 3~ ..., 15), whlch are supplied to thr~shold circuits 24.i (i ~ 1, 3, ..., 15) via lines 25.i (i = 1, 3, ..., 15) respectively.
The MTI uni~ is provided with a timing generator 27 for generating signals S to control the MTI unit in ~ime.
It will be clear that according to the invention other interpolation methods can be. used as wall. It is also possible to further reduce the number of cluttar maps. Thus, it has been shown that an especially effective clutter suppression is or.ly obtained if rlutter maps are compiled for output chann,els Ai (i ~ 0, 2, 4, 8, 12, 14).
For output channels Ai (i ~ 6, 7, 9, 10), the threshold unit uses the clutter map belonging to outpue channel A8, while for the other channels Ai (i = 1, 3, 5, 11, 13, l5), the abo~e-described ~nterpolation between two neighbou:ring output channels is applied.
If the radar apparatus in which the above-described MTI unit is applied, uses a staggered pulse repetition fxequency (two or more p.r.f.'s), it is possible to record a set of clutter maps as described above for the pulse repetition frequencies. The number of clutter maps will then double in case staggering implies the use of two p.r.f.'s. Staggering is important for the suppression of multiple-time-around echoes, because they take up different positions for the different p.r.f.'s. If for staggering p different p.r.f.'s are used, the number of clutter maps will be increased by a factor p.
By means of the above-described interpolation methods, the number of clutter maps can however ba decreased again. The combination of staggering on the one hand and interpolation on the other hand has the combined result of allowing a specially effect~ve clut~er suppression while suppressing multiple-time-axound echoes.
Claims (8)
1. Moving target indication unit comprising:
a. a doppler filter bank having n output channels Ai (i = 0, 1, 2, ..., n-l), said filter bank producing on said channels output signals derived from echoes returned from a plurality of azimuth cells;
b. a detection and registration unit electrically connected to the output channels and including means for determining and storing from the signals produced on k of said n output channels, for each of the azimuth cells, k respective parameters representative of the amount of clutter in said cells, where k ' 2, and for producing threshold values from the parameters, said unit further including interpolation means for processing at least certain ones of k parameters to determine at least one interpolated threshold value; and c. a plurality of threshold circuits electrically connected to the output channels and to the detection and registration unit, threshold levels of said circuits being set for said azimuth cells by respective one of said threshold values and interpolated threshold values.
a. a doppler filter bank having n output channels Ai (i = 0, 1, 2, ..., n-l), said filter bank producing on said channels output signals derived from echoes returned from a plurality of azimuth cells;
b. a detection and registration unit electrically connected to the output channels and including means for determining and storing from the signals produced on k of said n output channels, for each of the azimuth cells, k respective parameters representative of the amount of clutter in said cells, where k ' 2, and for producing threshold values from the parameters, said unit further including interpolation means for processing at least certain ones of k parameters to determine at least one interpolated threshold value; and c. a plurality of threshold circuits electrically connected to the output channels and to the detection and registration unit, threshold levels of said circuits being set for said azimuth cells by respective one of said threshold values and interpolated threshold values.
2. A moving target indication unit as in claim 1 where k = n.
3. A moving target indication unit as in claim 1 where the detection and registration unit determines parameters bi and bi+2 from output signals Ui and Ui+2 of output channels Ai and Ai+2, respectively, produces threshold values Bi and Bi+2 from the respective parameters bi and bi+2, and where the interpolation means produces from said parameters the threshold value Bi+1.
4. A moving target indication unit as in claim 3 where the interpolation means determines the parameters bi+1 (i = 0, 2, ....
n-2) in accordance with the relationship:
bi+1 =
n-2) in accordance with the relationship:
bi+1 =
5. A moving target indication unit as in claim 1, 2 or 3 where the detection and registration unit includes means for processing one of the stored parameters bi and an output signal Ui to obtain and store a new parameter bi.
6. A moving target indication unit as in claim 1, 2 or 3 where the echoes are obtained at p different pulse repetition frequencies and where the detection and registration unit is adapted for determining and storing said k parameters for each azimuth cell and for each different pulse repetition frequency.
7. A moving target indication unit as in claim 6 where k = p.n.
8. A moving target indication unit as in claim 6 where 2 ? k ? p.n.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL8800002 | 1988-01-04 | ||
| NL8800002A NL8800002A (en) | 1988-01-04 | 1988-01-04 | MOVING TARGET INDICATION UNIT. |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1320752C true CA1320752C (en) | 1993-07-27 |
Family
ID=19851539
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000587380A Expired - Lifetime CA1320752C (en) | 1988-01-04 | 1989-01-03 | Moving target indication unit |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US5049889A (en) |
| EP (1) | EP0323662B1 (en) |
| JP (1) | JP2554152B2 (en) |
| AU (1) | AU614102B2 (en) |
| CA (1) | CA1320752C (en) |
| DE (1) | DE3887748T2 (en) |
| NL (1) | NL8800002A (en) |
| NO (1) | NO173299C (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL8800002A (en) * | 1988-01-04 | 1988-04-05 | Hollandse Signaalapparaten Bv | MOVING TARGET INDICATION UNIT. |
| JPH03252581A (en) * | 1990-03-02 | 1991-11-11 | Mitsubishi Electric Corp | Radar device |
| NL9102125A (en) * | 1991-12-19 | 1993-07-16 | Hollandse Signaalapparaten Bv | RADAR DEVICE WITH A COHERENT CLUTTER FOLDER. |
| US5191337A (en) * | 1992-02-25 | 1993-03-02 | Hughes Aircraft Company | Ranging, detection and resolving in a multislope frequency modulated waveform radar system |
| US5357256A (en) * | 1993-08-17 | 1994-10-18 | Alliedsignal Inc. | Radar receiver with adaptive clutter threshold reference |
| NL9301552A (en) * | 1993-09-08 | 1995-04-03 | Hollandse Signaalapparaten Bv | Radar device. |
| NL9401767A (en) * | 1994-10-25 | 1996-06-03 | Hollandse Signaalapparaten Bv | Radar device. |
| US5831569A (en) * | 1996-11-01 | 1998-11-03 | Northrop Grumman Corporation | Method and apparatus for injecting synthetic pulses for increased transmitter stability |
| US6260759B1 (en) | 1998-08-11 | 2001-07-17 | Northrop Grumman Corporation | Method for tracking a target having substantially constrained movement |
| JP6339893B2 (en) * | 2014-08-29 | 2018-06-06 | 古野電気株式会社 | Clutter suppression device and radar device including the same |
| CN110865363A (en) * | 2019-11-01 | 2020-03-06 | 武汉滨湖电子有限责任公司 | Moving target display and detection synthesis method |
Family Cites Families (15)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3701149A (en) * | 1971-07-02 | 1972-10-24 | Us Navy | Frequency averaging controlled false alarm rate (cfar) circuit |
| FR2306453A1 (en) * | 1975-04-03 | 1976-10-29 | Nippon Electric Co | MOBILE TARGET INDICATION RADAR |
| US4093949A (en) * | 1976-05-26 | 1978-06-06 | Hughes Aircraft Company | Clutter tracker using a smoothed doppler frequency measurement |
| US4057800A (en) * | 1976-06-01 | 1977-11-08 | Grumman Aerospace Corporation | Multi-PRF signal processor system |
| DE2752338C2 (en) * | 1977-11-23 | 1983-11-17 | Siemens AG, 1000 Berlin und 8000 München | Radar receiver |
| FR2487078A1 (en) * | 1980-07-16 | 1982-01-22 | Thomson Csf | DEVICE FOR DETECTING MOBILE TARGETS IN A RADAR AND RADAR SYSTEM COMPRISING SUCH A DEVICE |
| US4503432A (en) * | 1981-12-17 | 1985-03-05 | The United States Of America As Represented By The Secretary Of The Army | Adaptive threshold detection utilizing a tapped charge transfer device delay line |
| US4536764A (en) * | 1982-09-29 | 1985-08-20 | Westinghouse Electric Corp. | Method of counting multiple targets in the post detection processing of a radar |
| IT1168614B (en) * | 1983-07-15 | 1987-05-20 | Selenia Ind Elettroniche | MTD DIGITAL PROCESSOR FOR SEARCH RADAR WITH BENCH OF DOPPLER FILTERS AND SYSTEM OF SELF-ADJUSTABLE THRESHOLDS DEPENDING ON THE DISORDER |
| JPS6024476A (en) * | 1983-07-21 | 1985-02-07 | Nec Corp | Radar equipment |
| US4652881A (en) * | 1984-01-10 | 1987-03-24 | Lewis Bernard L | Efficient adaptive filter bank |
| USH108H (en) * | 1985-10-15 | 1986-08-05 | The Government Of The United States | Radar doppler processor using a fast orthogonalization network |
| DE3689037D1 (en) * | 1985-12-23 | 1993-10-21 | Nec Corp | Radar system. |
| US4688044A (en) * | 1986-07-07 | 1987-08-18 | Hughes Aircraft Company | Multiple range interval clutter cancellation circuit |
| NL8800002A (en) * | 1988-01-04 | 1988-04-05 | Hollandse Signaalapparaten Bv | MOVING TARGET INDICATION UNIT. |
-
1988
- 1988-01-04 NL NL8800002A patent/NL8800002A/en not_active Application Discontinuation
- 1988-12-14 DE DE3887748T patent/DE3887748T2/en not_active Expired - Lifetime
- 1988-12-14 EP EP88202867A patent/EP0323662B1/en not_active Expired - Lifetime
- 1988-12-15 AU AU26969/88A patent/AU614102B2/en not_active Expired
- 1988-12-19 NO NO885627A patent/NO173299C/en not_active IP Right Cessation
- 1988-12-28 JP JP63335681A patent/JP2554152B2/en not_active Expired - Lifetime
-
1989
- 1989-01-03 CA CA000587380A patent/CA1320752C/en not_active Expired - Lifetime
- 1989-01-03 US US07/292,674 patent/US5049889A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| JP2554152B2 (en) | 1996-11-13 |
| NO885627D0 (en) | 1988-12-19 |
| US5049889A (en) | 1991-09-17 |
| AU614102B2 (en) | 1991-08-22 |
| NO173299B (en) | 1993-08-16 |
| NO173299C (en) | 1993-11-24 |
| AU2696988A (en) | 1989-07-06 |
| EP0323662B1 (en) | 1994-02-09 |
| DE3887748D1 (en) | 1994-03-24 |
| NO885627L (en) | 1989-07-05 |
| DE3887748T2 (en) | 1994-07-28 |
| NL8800002A (en) | 1988-04-05 |
| JPH026780A (en) | 1990-01-10 |
| EP0323662A1 (en) | 1989-07-12 |
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