Monopulse angle determination

• US 8,269,665 B1
• Filed: 01/29/2010
• Issued: 09/18/2012
• Est. Priority Date: 01/29/2010
• Status: Active Grant

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Urkowitz, Harry, Postell, Robert A., Lefferts, Robert E.
• Primary Examiner(s): Keith, Jack W
• Assistant Examiner(s): Bythrow, Peter
• Application Number:
  US12/696,248
• Time in Patent Office: 963 Days
• Field of Search: 342/80, 342/147, 342149-154, 342159-162, 342/194
• US Class Current: 342/80
• CPC Class Codes: G01S 13/284 using coded pulses
• CPC Class Codes: G01S 13/4418 with means for eliminating radar-dependent errors in angle measurements, e.g. multipath effects

Abstract

Modern tactical radars frequently use phase shifters to electronically specify or steer the spatial position of the antenna beam without requiring mechanical motion of the antenna. These phase shifters can only be set correctly for a specific frequency. If a waveform is transmitted through the antenna which consists of multiple segments which differ in frequency or modulation from that frequency used to steer the position of the beam, errors are introduced into the monopulse measurement. These monopulse errors are reduced or eliminated by correction factors. The monopulse errors are corrected by pre-computed factors or terms which result from the differences in frequency and modulation used in the waveform from the frequency used to steer or position the beam. Correction is also provided for radar altitude. These correction factors are easily pre-computed and applied only when needed to minimize the computational requirements.

Claims

1. A radar system, comprising:

a beam direction controller;

a transmitter for transmitting subpulses at nominal frequencies F with modulation which is capable of resulting in an actual average frequency different from frequencies F;

a monopulse receiver for receiving signals from a target, and for generating rho (ρ

) signals, each of which rho signals is a real component of one of eight complex monopulse ratios, four of which represent a Δ

α

angle and the other four of which represent a Δ

β

angle;

a polynomial processor coupled to said receiver, for producing uncorrected cosine differences of angular offsets of a target from a commanded beam pointing direction or angle cosines

cos(α

₀+δ

α

)−

cos α

₀

cos(β

₀+δ

β

)−

cos β

₀;

a multiplicative correction processor for multiplying said uncorrected cosine differences by a factor including (a) a frequency at which a polynomial is determined and (b) an actual average frequency of a particular subpulse, to thereby generate multiplied cosine differences for each subpulse;

a summing correction processor coupled to said multiplicative correction processor for adding to said multiplied cosine differences a correction term for compensating for apparent movement of the target arising in a particular direction from beam movement at each subpulse, to thereby generate a plurality of multiplicatively and additively compensated angles or angle cosine difference signals; and

an averaging arrangement coupled to said summing correction processor for averaging said angles or angle cosine difference signals over all subpulses of a pulse to thereby produce averaged angular difference signals representative of a location of the target,

wherein

ρ

=a real component of one of eight complex monopulse ratios;

Δ

α

=difference of half-antenna outputs corresponding to an α

direction;

Δ

β

=difference of half-antenna outputs corresponding to a β

direction;

α

₀=direction angle measured from a positive X axis to a beam direction line;

β

₀=direction anile measured from a positive Z axis to the beam direction line;

δ

α

=departure angle from beam direction angle α

₀; and

δ

β

=departure angle from beam direction angle β

₀.

2. A radar according to claim 1, wherein said summing correction processor coupled to said multiplicative correction processor further adds to said multiplied cosine differences a correction term for compensating for actual speed of light in an environment of said radar.

3. A radar according to claim 2, wherein said correction term for compensating for apparent movement is in the form of one of

4. A radar according to claim 1, further comprising a squint corrector coupled to said averaging arrangement, for summing a squint correction with said averaged angular difference signals to generate target angular information representative of a corrected direction of the target.

5. A radar system including a transmitter, a waveform generator coupled to said transmitter for driving said transmitter with sets of sequential pulses, each pulse of each of said sets being jump-frequency modulated relative to other pulses of the set to thereby define a plurality of subpulses for each said set of sequential pulses, said radar system comprising:

an antenna coupled to said transmitter, for transmitting electromagnetic signals in response to said sets of sequential subpulses, and for, in the presence of a target, generating separate return signals for each of said sequential subpulses of each set;

a receiver for receiving said return signals and for generating received signals, said received signals including a separate digital signal subpulse for each of said separate return signals;

a splitting arrangement for splitting said received signals into co-elevation and traverse difference component;

a monopulse processor for combining said co-elevation and traverse difference components and said sum component signal to provide monopulse ratios representing an uncorrected direction to the target; and

a monopulse correction processor for correcting the uncorrected direction to the target with corrections based on each subpulse frequency.

6. A radar system including a transmitter, a waveform generator coupled to said transmitter for driving said transmitter with sets of sequential pulses, each pulse of each of said sets being jump-frequency modulated relative to other pulses of the set, said radar system comprising:

an antenna coupled to said transmitter, for transmitting electromagnetic signals in response to said sets of sequential pulses, and for, in the presence of a target, generating separate return signals for each of said sequential pulses of each set;

a receiver for receiving said return signals and for generating received signals, said received signals including a separate digital signal for each of said separate return signals;

a splitting arrangement coupled to said receiver for splitting said received signals into vertical and horizontal difference components and a sum component;

a monopulse processor coupled to said splitting arrangement for combining said vertical and horizontal difference components and said sum component to provide a monopulse ratio; and

a monopulse ratio processor coupled to said monopulse processor for generating corrected direction of the target cos α

_target by solving

7. A receiver for, in the presence of a target, generating separate received signals for each sequential subpulse of a set of subpulses, said separate received signals including a separate digital signal subpulse for each of a plurality of separate return signals returned from a target, said receiver comprising:

a splitting arrangement for splitting said received signals into co-elevation and traverse difference components;

a monopulse processor for combining said co-elevation and traverse difference components and a sum component signal to provide monopulse ratios representing uncorrected direction to the target; and

a monopulse correction processor for correcting the uncorrected direction to the target with corrections based on each subpulse frequency.

8. A receiver for receiving radar return signals and for generating received signals, said received signals including a separate digital signal for each of said separate return signals, said receiver comprising:

a splitting arrangement coupled to said receiver for splitting said received signals into vertical and horizontal difference components and a sum component;

a beam steering controller;

a monopulse processor coupled to said splitting arrangement for combining said vertical and horizontal difference components and said sum component signal to provide a monopulse ratio; and

a monopulse ratio processor coupled to said monopulse processor for generating corrected direction of the target cos α

_target by solving

9. A radar system comprising:

a transmitter for transmitting subpulses;

a monopulse receiver for receiving return signals from a target, and for generating rho signals, each of which rho signal is a real component of one of eight complex monopulse ratios, four of which represent a Δ

α

angle and the other four of which represent a Δ

β

angle;

a polynomial processor coupled to said receiver, for producing uncorrected cosine differences of angular offsets of the target from the commanded beam pointing direction;

a multiplicative correction processor for multiplying said uncorrected cosine differences to generate multiplied cosine differences for each subpulse;

a summing correction processor for adding to said multiplied cosine differences a correction term for compensating for apparent movement of the target arising in a particular direction from beam movement at each subpulse, to generate a plurality of multiplicatively and additively compensated angles or angle cosine difference signals; and

an averaging arrangement for averaging said additively compensated angles or angle cosine difference signals over all subpulses of a pulse to thereby produce averaged angular difference signals representative of a location of the target;

where

Δ

α

=difference of half-antenna outputs corresponding to an α

direction; and

Δ

β

=difference of half-antenna outputs corresponding to a β

direction.

10. A radar system according to claim 9, wherein said summing correction processor adds to said multiplied cosine differences a correction term for compensating for actual speed of light in an environment of said radar.

11. A radar system according to claim 9, wherein said correction term for compensating for apparent movement is in the form of one of:

12. A radar system according to claim 9, further comprising a squint corrector coupled to said averaging arrangement, for summing a squint correction with said averaged angular difference signals to generate target angular information representative of a corrected direction of the target.

13. A radar system, comprising:

a beam direction controller;

a transmitter for transmitting subpulses at nominal frequencies;

a monopulse receiver for receiving signals from a target, and for generating rho signals, each of which rho signals is a component of one of a plurality of monopulse ratios;

a polynomial processor coupled to said monopulse receiver, for producing uncorrected cosine differences of angular offsets of a target from a commanded beam pointing direction;

a multiplicative correction processor for multiplying said uncorrected cosine differences by a factor to generate multiplied cosine differences for each subpulse;

a summing correction processor coupled to said multiplicative correction processor for adding to said multiplied cosine differences a correction term for compensating for apparent movement of the target arising in a direction from beam movement at each subpulse, to generate a plurality of multiplicatively and additively compensated angle cosine difference signals; and

an averaging arrangement coupled to said summing correction processor for averaging said angle cosine difference signals over all subpulses of a pulse to produce averaged angular difference signals representative of a location of the target.

14. A radar system according to claim 13, wherein said summing correction processor adds to said multiplied cosine differences a correction term for compensating for speed of light in an environment of said radar.

15. A radar system according to claim 14, wherein said correction term for compensating for apparent movement is in the form of one of:

16. A radar system according to claim 13, further comprising a squint corrector coupled to said averaging arrangement, for summing a squint correction with said averaged angular difference signals to generate target angular information representative of a corrected direction of the target.

17. A computer-implemented method for operating a radar system, comprising:

transmitting subpulses at nominal frequencies;

receiving signals from a target, and generating rho signals, where each of said rho signals is a component of one of a plurality of monopulse ratios;

producing uncorrected cosine differences of angular offsets of a target from a commanded beam pointing direction;

using a computer processor for carrying out the step of multiplying said uncorrected cosine differences by a factor to generate multiplied cosine differences for each subpulse;

using a computer processor for carrying out the step of adding to said multiplied cosine differences a correction term for compensating for apparent movement of the target arising in a direction from beam movement at each subpulse, to generate a plurality of multiplicatively and additively compensated angle cosine difference signals; and

averaging said angle cosine difference signals over all subpulses of a pulse to produce averaged angular difference signals representative of a location of the target;

using said averaged angular difference signals to determine whether a target location is a newly detected target or is a new position of a previously-identified target; and

if the target location is a newly identified target, establishing a new target track to follow the target, or

if the target location is a previously-identified target, using the target location to update a track on the previously-identified target.

18. A computer-implemented method according to claim 17, wherein said adding step adds to said multiplied cosine differences a correction term for compensating for speed of light in an environment of said radar.

19. A computer-implemented method according to claim 18, wherein said correction term for compensating for apparent movement is in the form of one of:

20. A computer-implemented method according to claim 17, comprising the further step of summing a squint correction with said averaged angular difference signals to generate target angular information representative of a corrected direction of the target.