Log magnitude pulse interference detection for a radar system

• US 4,710,772 A
• Filed: 12/05/1985
• Issued: 12/01/1987
• Est. Priority Date: 12/05/1985
• Status: Expired due to Term

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Cantwell, Robert H., Marksteiner, William K., Hansen, V. Gregers
• Primary Examiner(s): Tubbesing, T. H.
• Assistant Examiner(s): GREGORY, BERNARR E
• Application Number:
  US06/804,946
• Time in Patent Office: 726 Days
• Field of Search: 343/5 CE, 343/5 CF, 343/5 DP, 343/5 NQ, 343/7 AG, 343/7 PL, 342/91-94, 342/102, 342/103, 342/159-162, 342/194-197, 342/203
• US Class Current: 342/92
• CPC Class Codes: G01S 7/2928 Random or non-synchronous interference pulse cancellers
• CPC Class Codes: G01S 7/34 Gain of receiver varied automatically during pulse-recurrence period, e.g. anti-clutter gain control
• CPC Class Codes: H03G 3/3052 in bandpass amplifiers (H.F. or I.F.) or in frequency-changers used in a (super)heterodyne receiver H03G3/32, H03G3/34 take precedence
• CPC Class Codes: H03G 7/007 of digital or coded signals

Abstract

A radar receiver having a feed-forward control circuit for adjusting the automatic gain control (AGC) setting in 6 dB increments for each range cell in a next sweep based on the AGC setting of each corresponding range cell in the present sweep, the magnitude of the larger of the in-phase (I) or quadrature (Q) components of the video signals of the present sweep from an A/D converter, the status of present sweep and previous sweep A/D limit conditions, and a selected guardband thereby holding the level of the radar return signal within the dynamic range of the A/D converter. The AGC setting is adjusted using a switchable attenuator which changes the level of the video signal into the A/D converter in 6 dB increments, each increment corresponding to a common I and Q data exponent directly used for floating point signal processing. A pulse interference detection and signal replacement apparatus and method utilizes an 8-bit log magnitude representation of each range cell sample generated from a floating point exponent and reduced precision mantissa components to detect a range cell pulse of interference at a specific range M and causes replacement of the range cell sample with an interpolated value determined from the average of the radar return signals of adjacent sweeps at range M.

Claims

1. In a radar system wherein received signals having amplitudes which may vary within a wide range of possible amplitudes are processed using automatic gain control (AGC), a pulse interference detection apparatus comprising:

means for converting a fixed point data representation of an in-phase (I) component and a quadrature (Q) component for each of said received signals to a floating point data representation having a mantissa and an exponent, said mantissa having at least one or more bits based on desired accuracy;

means coupled to said converting means and in response to an AGC level word for generating a log magnitude value for each of said received signals; and

means coupled to said log magnitude generating means for detecting a pulse of interference to one of said received signals in a sweep N-1 at range M based on an examination of said log magnitude value of adjacent sweeps N and N-2 at said range M.

2. The radar system as recited in claim 1 wherein said log magnitude value generating means comprises:

means for generating a log magnitude mantissa correction value in response to a normalized mantissa of each of said in-phase (I) and quadrature (Q) components for each of said received signals and a denormalizing control word;

first adder means for adding said log magnitude mantissa correction value to a largest exponent of said in-phase (I) and quadrature (Q) components for each of said received signals; and

second adder means coupled to said first adder means for adding an output of said first adder means to said AGC level word to obtain said log magnitude value, said AGC level word representing an attenuator factor applied to each of said received signals.

3. The radar system as recited in claim 2 wherein:

said radar system automatic gain control comprises means for selecting said largest exponent.

4. The radar system as recited in claim 2 wherein:

said largest exponent having a least significant bit scaled for 6 dB increments is aligned for adding starting at a 6 dB scaled bit of said log magnitude mantissa correction value.

5. The radar system as recited in claim 2 wherein:

said AGC level word having a least significant bit scaled for 6 dB increments is aligned for adding starting at a 6 dB scaled bit of said output of said first adder means.

6. The radar system as recited in claim 2 wherein:

said normalized mantissa for each of said in-phase (I) and quadrature (Q) components comprises an absolute value for improving the accuracy of said log magnitude value.

7. The radar system as recited in claim 2 wherein:

said log magnitude mantissa correction value being determined by four most significant bits of said normalized mantissa of each of said in-phase (I) and quadrature (Q) components and two bits of said denormalizing control word for providing said log magnitude value having eight bits with a measurement accuracy of at least 3/4 dB and a dynamic range of at least 102 dB for each of said received signals.

8. The radar system as recited in claim 1 wherein said detecting means comprises:

means for storing log magnitude values Y₂, X and Y₁ for said adjacent range sweeps N, N-1 and N-2;

means coupled to said storing means of said Y₁ and Y₂ values for generating an average value of said Y₁ and Y₂ log magnitude values;

means for adding said average value to a threshold level forming a sum; and

means coupled to said adding means for comparing said sum of said average value and said threshold level to said X value wherein a pulse interference signal is generated when said X value is greater than said sum;

9. The radar system as recited in claim 8 wherein:

said detecting means further comprises inverter means for providing a ones complement value of said sum; and

said comparing means comprises an adder having a first input of said X value and a second input of said ones complement value, thereby providing a carry-out from said adder means when said X value is greater than said sum, said carry-out being said pulse interference signal.

10. In a radar system wherein received signals having amplitudes which may vary within a wide range of possible amplitudes are processed using automatic gain control (AGC), a pulse interference detection apparatus comprising:

means for converting a fixed point data representation of an in-phase (I) component and a quadrature (Q) component for each of said received signals to a first normalized floating point data representation having a mantissa and an exponent, said mantissa having at least one or more bits based on desired accuracy;

means coupled to said converting means and in response to an AGC level word for generating a log magnitude value for each of said received signals;

means coupled to said log magnitude generating means for detecting a pulse of interference to one of said received signals in a sweep N-1 at range M based on an examination of said log magnitude value of adjacent sweeps N and N-2 at said range M and generating a pulse interference detection signal when said pulse of interference is detected;

means for generating a second normalized floating point data representation of said received signals in response to said fixed point data representation for each of said amplitudes of said received signals and said AGC level word; and

floating point interpolator means coupled to said second floating point data generating means and said interference detecting means for producing interpolated data to replace said pulse of interference for one of said received signals at range M of sweep N-1 in response to said generating of said pulse interference detection signal.

11. The radar system as recited in claim 10 wherein said log magnitude value generating means comprises:

means for generating a log magnitude mantissa correction value in response to a normalized mantissa of each of said in-phase (I) and quadrature (Q) components for each of said received signals and a denormalizing control word;

first adder means for adding said log magnitude mantissa correction value to a largest exponent of said in-phase (I) and quadrature (Q) components for each of said received signals; and

second adder means coupled to said first adder means for adding an output of said first adder means to said AGC level word to obtain said log magnitude value, said AGC level word representing an attenuator factor applied to each of said received signals.

12. The radar system as recited in claim 11 wherein:

said radar system automatic gain control comprises means for selecting said largest exponent;

13. The radar system as recited in claim 11 wherein:

said largest exponent having least significant bit scaled for 6 dB increments is aligned for adding starting at a 6 dB scaled bit of said log magnitude mantissa correction value.

14. The radar system as recited in claim 11 wherein:

said AGC level word having a least significant bit scaled for 6 dB increments is aligned for adding starting at a 6 dB scaled bit of said output of said first adder means.

15. The radar system as recited in claim 11 wherein:

said normalized mantissa for each of said in-phase (I) and quadrature (Q) components comprises an absolute value for improving the accuracy of said log magnitude value.

16. The radar system as recited in claim 11 wherein:

said log magnitude mantissa correction value being determined by four most significant bits of said normalized mantissa of each of said in-phase (I) and quadrature (Q) components and two bits of said denormalizing control word for providing said log magnitude value having eight bits with a measurement accuracy of at least 3/4 dB and a dynamic range of at least 102 dB for each of said received signals.

17. The radar system as recited in claim 10 wherein:

said floating point interpolator means produces said interpolated data for sweep N-1 by determining an average of the sum of said floating point representation of said received signals in sweeps N and N-2 adjacent to sweep N-1 at range M.

18. The radar system as recited in claim 10 wherein said detecting means comprises:

means for storing log magnitude values Y₂, X and Y₁ for said adjacent range sweeps N, N-1 and N-2;

means coupled to said storing means of said Y₁ and Y₂ values for generating an average value of said Y₁ and Y₂ log magnitude values; and

means coupled to said adding means for comparing said sum of said average value and said threshold level to said X value wherein a pulse interference signal is generated when said X value is greater than said sum.

19. The radar system as recited in claim 18 wherein:

said detecting means further comprises inverter means for providing a ones complement value of said sum; and

said comparing means comprises an adder having a first input of said X value and a second input of said ones complement value, thereby providing a carry-out from said adder means when said X value is greater than said sum, said carry-out being said pulse interference signal.

20. A pulse interference detector comprising:

means for storing log magnitude values Y₂, X and Y₁ for adjacent range sweeps N, N-1 and N-2;

means coupled to said storing means of said Y₁ and Y₂ values for generating an average value of said Y₁ and Y₂ log magnitude values;

means for adding said average value to a threshold level forming a sum;

inverter means coupled to said adding means for providing a ones complement value of said sum;

means coupled to said inverter means for comparing said sum of said average value and said threshold level to said X value wherein a pulse interference signal is generated when said X value is greater than said sum; and

said comparing means comprises an adder having a first input of said X value and a second input of said ones complement value, thereby providing a carry-out from said adder means when said X value is greater than said sum, said carry-out being said pulse interference signal.

21. In a radar system wherein received signals having amplitudes which may vary within a wide range of possible amplitudes are processed using automatic gain control (AGC), a method of detecting a pulse of interference comprising the steps of:

converting a fixed point data representation of an in-phase (I) and a quadrature (Q) components for each of said received signals to a normalized floating point data representation having a mantissa and an exponent, said mantissa having at least one most significant bit for increased precision;

generating a log magnitude value for each of said received signals in response to said normalized floating point data representative and an AGC level word; and

detecting a pulse of interference to one of said received signals in a sweep N-1 at range M based on an examination of said log magnitude value of adjacent sweeps N and N-2 at said range M.

22. The method as recited in claim 21 wherein said step of generating a log magnitude value comprises the steps of:

generating a log magnitude mantissa correction value in response to said normalized mantissa of each of said in-phase (I) and quadrature (Q) components for each of said received signals and a denormalizing control word;

adding said log magnitude mantissa correction value to a largest exponent of said in-phase (I) and quadrature (Q) components for each of said received signals; and

adding an output of said first adder means to said AGC level word to obtain said log magnitude value, said AGC level word representing an attenuator factor applied to each of said received signals.

23. The method as recited in claim 21 wherein said step of detecting a pulse of interference comprises the steps of:

storing log magnitude values Y₂, X and Y₁ for said adjacent range sweeps N, N-1 and N-2;

generating an average value of said Y₁ and Y₂ log magnitude values;

adding said average value to a threshold level forming a sum;

comparing said sum of said average value and said threshold level to said X value; and

generating a pulse interference signal when said X value is greater than said sum.

24. In a radar system wherein received signals having amplitudes which may vary within a wide range of possible amplitudes are processed using automatic gain control (AGC), a method of detecting and replacing a pulse of interference comprising the steps of:

converting a fixed point data representation of an in-phase (I) and a quadrature (Q) components for each of said received signals to a first normalized floating point representation having a mantissa and an exponent, said mantissa having at least one most significant bit for increased precision;

generating a log magnitude value for each of said received signals in response to said normalized floating point data representation and an AGC level word;

detecting a pulse of interference to one of said received signals in a sweep N-1 at range M based on an examination of said log magnitude value of adjacent sweeps N and N-2 at said range M;

generating a pulse interference detection signal when said pulse of interference is detected;

generating a second normalized floating point data representation of said received signals in response to said fixed point data representation for each of said amplitudes of said received signals and said AGC level word; and

producing interpolated data from said second normalized floating point data representation of said received signals to replace said pulse of interference for one of said received signals at range M of sweep N-1 in response to said generating of said pulse interference detection signal.

25. The method as recited in claim 24 wherein said step of generating a log magnitude value comprises the steps of:

generating a log magnitude mantissa correction value in response to said normalized mantissa of each of said in-phase (I) and quadrature (Q) components for each of said received signals and a denormalizing control word;

adding said log magnitude mantissa correction value to a largest exponent of said in-phase (I) and quadrature (Q) components for each of said received signals; and

adding an output of said first adder means to said AGC level word to obtain said log magnitude value, said AGC level word representing an attenuator factor applied to each of said received signals.

26. The method as recited in claim 24 wherein said step of detecting a pulse of interference comprises the steps of:

storing log magnitude values Y₂, X and Y₁ for said adjacent range sweeps N, N-1 and N-2;

generating an average value of said Y₁ and Y₂ log magnitude values;

adding said average value to a threshold level forming a sum;

comparing said sum of said average value and said threshold level to said X value; and

generating a pulse interference signal when said X value is greater than said sum.

27. The method of detecting a pulse of interference in a radar system comprising the steps of:

storing log magnitude values Y₂, X and Y₁ for adjacent range sweeps N, N-1 and N-2;

generating an average value of said Y₁ and Y₂ log magnitude values;

adding said average value to a threshold level forming a sum;

generating a ones complement value of said sum;

"comparing said ones complement of said sum of said average value and of said threshold level to said X value; and

".

generating a pulse interference signal when said X value is greater than said sum.