GB2261787A - Radar receiver systems - Google Patents

Radar receiver systems Download PDF

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Publication number
GB2261787A
GB2261787A GB8524883A GB8524883A GB2261787A GB 2261787 A GB2261787 A GB 2261787A GB 8524883 A GB8524883 A GB 8524883A GB 8524883 A GB8524883 A GB 8524883A GB 2261787 A GB2261787 A GB 2261787A
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GB
United Kingdom
Prior art keywords
pulses
interference
pulse
receiver system
filter
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.)
Granted
Application number
GB8524883A
Other versions
GB2261787B (en
GB8524883D0 (en
Inventor
Nigel Charles Trueman Coote
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.)
Plessey Co Ltd
BAE Systems Electronics Ltd
Original Assignee
GEC Marconi Ltd
Plessey Co Ltd
Marconi Co Ltd
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by GEC Marconi Ltd, Plessey Co Ltd, Marconi Co Ltd filed Critical GEC Marconi Ltd
Priority to GB8524883A priority Critical patent/GB2261787B/en
Priority to DE19863644892 priority patent/DE3644892A1/en
Priority to FR8706429A priority patent/FR2686156A1/en
Priority to IT2131787A priority patent/IT1237562B/en
Priority to SE8703019A priority patent/SE8703019L/en
Publication of GB8524883D0 publication Critical patent/GB8524883D0/en
Publication of GB2261787A publication Critical patent/GB2261787A/en
Application granted granted Critical
Publication of GB2261787B publication Critical patent/GB2261787B/en
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
    • G01S7/00Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/28Details of pulse systems
    • G01S7/285Receivers
    • G01S7/292Extracting wanted echo-signals
    • G01S7/2923Extracting wanted echo-signals based on data belonging to a number of consecutive radar periods
    • G01S7/2928Random or non-synchronous interference pulse cancellers

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Radar Systems Or Details Thereof (AREA)

Abstract

A clutter-reducing digital filter 6 spreads out impulsive interference making it difficult to recognise the presence of impulsive interference. To solve this a buffer store 8 stores a predetermined number of filtered echo pulses and pattern recognition means 10 responsive to the stored pulses contemporaneously for recognises a predetermined pulse amplitude pattern which signifies the presence of an interference pulse. A feedback cancellation operation 11, 13 suppresses the interference pulse. <IMAGE>

Description

IMPROVEMENTS IN AND RELATING TO RECEIVER SYSTEMS The present invention relates to a receiver system and more particularly to a receiver system having means for suppressing interference signals from received signals.
In a known radar receiver system a received echo signal is fed to an analogue-to-digital (A/D) converter. The received signal may include echo signals from a moving object which it is desired to detect and also clutter signals the main portion of which result from transmitted pulses being reflected from ground based objects. As the objects on the ground have no motion of their own the clutter signals form a predictable pattern and can be suppressed by feeding the output signal from the A/D converter to a suitable digital filter.
Although the digital filter will suppress the clutter signals it does not suppress impulse interference. Impulse interference may typically arise when there is another pulsed radar transmitter operating in the area on a different pulsed repetition frequency. The interference is usually many times larger than the wanted echo but will only be received when its arrival corresponds to ones own receiver system being in its receiving mode. As the receiver system is only intermittently in a receiving mode the interference usually affects only isolated echo pulses, i.e. has an impulse nature.
One of the problems in attempting to cancel interference pulses, particularly a problem in radar receiver systems, is that the interference pulses are difficult to recognise if the cancellation is attempted before clutter reduction in the digital filter. This arises because the clutter signals are usually vastly greater in magnitude than the required echo signals and also tend to mask any interference pulse. As a result if one attempts to remove the interference pulse before the filter stage then one may also remove a part of the clutter signals which are themselves therefore disrupted and this in turn hinders their suppression in the digital filter.On the other hand if suppress ion of the interference pulses is attempted after clutter reduction the interference pulse will on passing through the filter, particularly in the case with a recursive filter, have spread out to subsequent pulses at which stage it is difficult to correct for the full effect of tie interference pulse.
According to the present invention there is provided a receiver system comprising an analogue to digital converter for receiving a signal, a digital filter for receiving output signals from the analogue to digital converter, a buffer store operative to store a predetermined number of filtered pulses and pattern recognition means responsive to the stored pulses for recognising contemporaneously a predetermined pulse amplitude which signifies the presence of an interference pulse and for feeding a modified train of pulses back to the input of the digital filter to modify subsequent output signals from the digital filter so as to be substantially free from the effects of impulse interference.
In a preferred embodiment the pattern recognition means is adapted to calculate in digital form the effect of the detected impulse interference on the echo pulse train, and is operative to transmit a feedback signal to the buffer store to modify the stored pulse train in the buffer store so that the main effect of the impulse interference on the stored pulse train is cancelled.
In a preferred embodiment of the present invention the pattern recognition means recognizes a pulse amplitude pattern in consecutive filtered pulses in the buffer store, which pattern signifies the presence and position in time of the interference pulse.
By utilising a buffer store in which a predetermined number of consecutive filtered pulses are stored, feedback can be applied selectively to one or more stored signals, to facilitate recognition and suppression of interference pulses after clutter suppression.
In a preferred embodiment the receiver system is a radar receiver system, the filter operative to suppress clutter from radar echo return pulses transmitted from the output of the analogue-to-digital converter and the buffer store operative to store the predetermined number of filtered radar echo return pulses.
In one embodiment of the present invention the digital filter is an "n" pole recursive filter. The buffer store has means provided to buffer the inputs and outputs of the digital filter for a predetermined number of pulses, preferably sequential. This predetermined number is preferably less than or equal to the number "n" of poles associated with the recursive filter and preferably such that after said predetermined number of pulses the response function of the filter has passed its peak.
In another embodiment of the present invention the digital filter is in the form of a finite impulse response filter.
The pattern recognition means may in one embodiment have means for calculating a threshold amplitude, the threshold amplitude being a function of the average amplitude of a predetermined number of previously received filtered pulses. Means may be provided for comparing the amplitudes of at least some of the filtered pulses stored in the buffer store with the threshold amplitude so as to identify which, if any, of the filtered pulses have an amplitude greater than the threshold amplitude. The pattern recognition has in a preferred embodiment means for comparing the amplitude of a filtered pulse in the pulse train stored in the buffer store with the amplitude of another pulse to determine on which input pulse the interference occurred.
An aspect of the present invention is the provision of a method of suppressing interference pulses in received echo return pulses, including the steps of receiving the echo return pulses, filtering out clutter interference from the echo return pulses, storing a filtered echo return pulse train which is substantially free of clutter interference in a buffer store, identifying the presence of an interference pulse, calculating the effect of the interference pulse on an expected echo return pulse train unaffected by the interference pulse and providing a feedback signal to the buffer and to a filter to suppress the effects of the interference pulse.
Figure 1 is a block diagram of a radar receiver system in accordance with one embodiment of the present invention; and, Figure 2 is an example of a pulse train under test in the pattern recognition stage of Figure 1.
Referring to Figure 1 a radar receiver 2 is operative to receive echo pulses during a short time interval following each transmission, the delay between transmit and receive corresponding to the range of the echo. The received signal pulse is a complete signal in the sense that in addition to including the echo from the wanted moving target, and impulse interference, if any, it will also include clutter signals. The complete signal received by the radar receiver 2 after each transmit pulse is fed to an analogue-to-digital (A/D) converter 4 which records in digital form, the amplitude of the complete signal.
The train of "pulses" (i.e. train of digitised signal amplitudes) transmitted from the output of the A/D converter 4 is fed to the input of an "n" pole recursive (digital) filter 6 the output of which is dependent on its last "n" input and "n" output pulses.
The recursive filter 6 is designed to suppress the clutter signals whose pulse trains have pattern characteristics which can be predicted. The output signal, which is now suppressed of clutter signals, from the recursive filter 6 is transmitted to an input of a buffer store 8 which forms part of a digital processor which also comprises a pattern recognition stage 10. The buffer store 8 is programmed to store a predetermined number of pulses and in the embodiment described herein the buffer store 8 is programmed to store four consecutive pulses from the output of the recursive filter 6. If an interference pulse is present at the receiver its effect will be spread into all subsequent outputs of the recursive filter 6, unless it is cancelled.
The buffer store 8 is coupled to the pattern recognition stage 10 which is programmed to identify changes in the amplitudes of the stored pulses in the buffer store 8 which changes are a result of impulse interference. To this end the pattern recognition stage 10 is programmed to calculate continually an average value for the amplitude of a number of previously stored pulses all of which were substantially free of the effects of impulse interference.
The average amplitude A of for example thirty two such previously stored pulses is determined. The pattern recognition stage 10 continually sets a threshold value for amplitude which is dependent on the average amplitude A for the pulses. It has been found in practice that the effect of any significant impulse interference on a normal train of echo pulses usually substantially increases the amplitude of one or more of those pulses as received by the buffer store 8. In the embodiment described it will be assumed that the threshold amplitude is set to a value four times greater than the average amplitude A. Thus the threshold amplitude is set at a value equal to 4A.
Having calculated the threshold amplitude the pattern recognition stage 10 then proceeds to compare the actual amplitude of some of the pulses stored in the buffer store 8 with the threshold amplitude. The pattern recognition stage 10 is also programmed to compare the relative amplitudes of the pulses stored in the buffer store 8 as this is indicative of the position in time of the interference pulse. The pattern recognition stage 10 calculates in digital form the effect of the impulse interference on the echo pulse train, assuming this effect is dominant at its peak, and transmits a feedback signal along a line 11 to the buffer store 8 in order to modify the stored pulse train in the buffer store 8 so that the main effect of the impulse interference is removed.The modified train of pulses is then fed back along a line 13 to the input of the recursive filter the outputs from which should subsequently be substantially free from the effects of impulse interference.
The above process will be illustrated further with regard to the pulse train in figure 2 in which the pulse amplitudes Pn-l, Pn-2, Pn-3, and Pn-4 have been stored in the buffer store 8. The threshold value T is calculated within the pulse recognition stage 10 as being equal to 4A and for the sake of this example both Pn-l and Pn-2 are both shown as having an amplitude slightly above 4A. The threshold testing in the pulse recognition stage 10 will show that both pulse amplitudes Pn-l and Pn-2 are above the threshold value 4A and the pattern recognition stage 10 is programmed to recognise the stored pulse train as having been affected by an interference pulse.A sub-routine within the pattern recognition stage 10 then compares pulse amplitudes, and for example would determine that the amplitude of pulse n-2 was greater than the amplitude of pulse n thereby deducing that the impulse interference occurred at pulse n-4. With this data the pulse train of figure 2 can be modified by the feedback signal along the line 11 to suppress the effect of the impulse on the pulse train stored in the buffer 8. Data on the modified pulse train is also fed back to the input of the recursive filter 6 thereby modifying subsequent output signals from the recursive filter 6 and suppressing the effect of the interference pulse from these outputs.
The output signal from the pattern recognition stage 10 is therefore a signal in which clutter and interference pulses have been suppressed. The output signal is fed to a processor 12 which calculates the location and speed of the moving object which data is then fed to a detection circuit 14.
Although the invention described above has been described in relation to a radar receiver system its applications can extend to other receiver systems, for example a sonar receiver system. Also other varieties of digital filter can be used and the pattern recognition algorithms within the digital processor will vary in detail, according to the shape of the response function from the digital filter. The threshold and relative amplitude tests for the pulses can be performed on complex or real data, and a number of approximations can be made to facilitate the real time processing task.

Claims (13)

CLAIMS:
1. A receiver system comprising an analogue to digital converter for receiving a signal, a digital filter for receiving output signals from the analogue to digital converter, a buffer store operative to store a predetermined number of filtered pulses and pattern recognition means responsive to the stored pulses for recognizing contemporaneously a predetermined pulse amplitude pattern which signifies the presence of an interference pulse and for feeding a modified train of pulses back to the input of the digital filter to modify subsequent output signals from the digital filter so as to be substantially free from the effects of impulse interference.
2. A receiver system as claimed in claim 1 wherein the pattern recognition means is adapted to calculate in digital form the effect of the detected impulse interference on the echo pulse train, and is operative to transmit a feedback signal to the buffer store to modify the stored pulse train in the buffer store so that the main effect of the impulse interference on the stored pulse train is cancelled.
3. A receiver system as claimed in claim 1 or 2 wherein the pattern recognition means recognizes a pulse amplitude pattern in consecutive filtered pulses in the buffer store, which pattern signifies the presence and position in time of the interference pulse.
4. A receiver system as claimed in any one of claims 1 to 3 wherein the pattern recognition means has means for calculating a threshold amplitude, the threshold amplitude being a function of the average amplitude of a predetermined number of filtered pulses previously received by the pulse recognition means, means also being provided for comparing the amplitudes of at least some of the filtered pulses stored in the buffer store with the threshold amplitude so as to identify which, if any, of the filtered pulses has an amplitude greater than or equal to the threshold amplitude.
5. A receiver system as claimed in claim 4 wherein the pattern recognition has means for comparing the amplitudes of filtered pulses in the buffer store with the amplitude of another pulse or pulses to determine the position in time at which the impulse interference occurred.
6. A receiver system as claimed in any one of claims 1 to 5 wherein the digital filter is an "n" pole recursive filter.
7. A receiver system as claimed in claim 6 wherein the buffer store is operative to buffer the inputs and outputs of the digital filter for a predetermined number of pulses less than or equal to the number "n" of poles associated with the recursive filter and such that after said predetermined number of pulses the response function of the filter has passed its peak.
8. A receiver system as claimed in any one of claims 1 to 5 wherein the digital filter is a finite impulse response filter.
9. A receiver system as claimed in any one of claims 1 to 8 wherein the receiver system is a radar receiver system, the filter being operative to suppress clutter from radar echo return pulses and the buffer store being operative to store a predetermined number of filtered radar echo return pulses.
10. A receiver system as claimed in any one of claims 1 to 8 wherein the receiver system is a sonar receiver system, the filter being operative to suppress clutter from sonar echo return pulses and the buffer store being operative to store a predetermined number of filtered sonar echo return pulses.
11. A method of suppressing interference pulses in received echo return pulses including the steps of receiving the echo return pulses, filtering out clutter interference from the echo return pulses by means of a digital filter, storing a filtered echo return pulse train which is substantially free of clutter interference in a buffer store, identifying the presence of an interference pulse, calculating the effect of the interference pulse on an expected echo return pulse train unaffected by the interference pulse and providing a feedback signal to the buffer and the digital filter to suppress the effects of the interference pulse on the echo return pulse train.
12. A method of suppressing interference pulses in received echo return pulses substantially as hereinbefore described with reference to figures 1 and 2 of the accompanying drawing.
13. A receiver system substantially as herinbefore described with reference to figure 1 of the accompanying drawing.
GB8524883A 1985-10-09 1985-10-09 Improvements in and relating to receiver systems Expired - Fee Related GB2261787B (en)

Priority Applications (5)

Application Number Priority Date Filing Date Title
GB8524883A GB2261787B (en) 1985-10-09 1985-10-09 Improvements in and relating to receiver systems
DE19863644892 DE3644892A1 (en) 1985-10-09 1986-10-08 RECEIVER ARRANGEMENT
FR8706429A FR2686156A1 (en) 1985-10-09 1987-05-05 Receiving system
IT2131787A IT1237562B (en) 1985-10-09 1987-07-16 RECEIVER SYSTEMS
SE8703019A SE8703019L (en) 1985-10-09 1987-07-31 receiver

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB8524883A GB2261787B (en) 1985-10-09 1985-10-09 Improvements in and relating to receiver systems

Publications (3)

Publication Number Publication Date
GB8524883D0 GB8524883D0 (en) 1993-01-27
GB2261787A true GB2261787A (en) 1993-05-26
GB2261787B GB2261787B (en) 1993-10-06

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GB8524883A Expired - Fee Related GB2261787B (en) 1985-10-09 1985-10-09 Improvements in and relating to receiver systems

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DE (1) DE3644892A1 (en)
GB (1) GB2261787B (en)
IT (1) IT1237562B (en)
SE (1) SE8703019L (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005024459A2 (en) * 2003-08-29 2005-03-17 Raytheon Company Asynchronous pulse detector for a radar receiver
EP1494043A3 (en) * 2003-07-02 2005-04-27 M/A-Com, Inc. Short-range vehicular radar system
GB2437589B (en) * 2006-02-14 2009-12-16 Furuno Electric Co Navigational aid and carrier sense technique

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1420018A (en) * 1972-02-28 1976-01-07 Philips Electronic Associated Radar apparatus
GB1548326A (en) * 1976-08-13 1979-07-11 Raytheon Co Apparatus having interference rejection

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1420018A (en) * 1972-02-28 1976-01-07 Philips Electronic Associated Radar apparatus
GB1548326A (en) * 1976-08-13 1979-07-11 Raytheon Co Apparatus having interference rejection

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1494043A3 (en) * 2003-07-02 2005-04-27 M/A-Com, Inc. Short-range vehicular radar system
WO2005024459A2 (en) * 2003-08-29 2005-03-17 Raytheon Company Asynchronous pulse detector for a radar receiver
WO2005024459A3 (en) * 2003-08-29 2005-05-26 Raytheon Co Asynchronous pulse detector for a radar receiver
GB2437589B (en) * 2006-02-14 2009-12-16 Furuno Electric Co Navigational aid and carrier sense technique
US7693177B2 (en) 2006-02-14 2010-04-06 Furuno Electric Company, Ltd. Navigational aid and carrier sense technique

Also Published As

Publication number Publication date
GB2261787B (en) 1993-10-06
IT1237562B (en) 1993-06-08
GB8524883D0 (en) 1993-01-27
DE3644892A1 (en) 1993-07-08
SE8703019D0 (en) 1987-07-31
SE8703019L (en) 1993-04-29

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Legal Events

Date Code Title Description
730A Proceeding under section 30 patents act 1977
PCNP Patent ceased through non-payment of renewal fee

Effective date: 19941009