Dual synthetic aperture radar system

• US 7,109,911 B1
• Filed: 08/11/2003
• Issued: 09/19/2006
• Est. Priority Date: 04/01/2002
• Status: Expired due to Fees

• Current Assignee: Thomas J. Cataldo
• Original Assignee: Thomas J. Cataldo
• Inventors: Cataldo, Thomas J.
• Primary Examiner(s): Lobo, Ian J.
• Application Number:
  US10/637,294
• Time in Patent Office: 1,135 Days
• Field of Search: 342/25, 342/159, 342/160, 342/195, 342/196, 342/25.R, 342/25.A, 342/25.B, 342/25.D, 342/25.F
• US Class Current: 342/25.00R
• CPC Class Codes: G01S 13/90 using synthetic aperture techniques , e.g. synthetic aperture radar [SAR] techniques
• CPC Class Codes: G01S 13/9092 combined with monopulse techniques

Abstract

The dual synthetic aperture array system processes returns from the receiving arrays. The two identical receiving arrays employing displaced phase center antenna techniques subtract the corresponding spectrally processed data to cancel clutter. It is further processed that a moving target is detected and its velocity, angular position and range is measured, in or out of the presence of clutter. There are many techniques presented in the disclosure. These techniques are basically independent but are related based on common set of fundamental set of mathematical equations, understanding of radar principles and the implementations involved. These many techniques may be employed singly and/or in combination depending on the application and accuracy required. They are supported by a system that includes, optimization of the number of apertures, pulse repetition frequencies, DPCA techniques to cancel clutter, adaptive techniques to cancel clutter, motion compensation, weighting function for clutter and target, and controlling the system in most optimum fashion to attain the objective of the disclosure.

Claims

1. In a transmission array with a dual receiving array, synthetic aperture radar system, a method for detecting the position of a moving target, clutter and target vectors being indeterminate, comprising the steps of:

a) positioning a first and second receiving array apart from the transmission array in a spaced relationship upon a moving platform;

b) utilizing a displaced phase center antenna methodology

 

to detect a moving target, and measuring data including but not limited to its range, relative radial velocity, and azimuth, wherein said data measured of said array 1 and said array 2 is delayed at least once for at least one interval in becoming a newly recorded data set,

c) determining a correction factor w_c and w_m for

 

imperfections of measurements of Displaced Phase Center Antenna in said first array and said second array, which vary with azimuth for clutter and target;

d) providing a phase correction, due to inexact match of platform travel to the pulse repetition time, for said second delay pulses in comparison with said first delay pulses and subtracting second array corresponding filters from said first array;

e) utilizing a clutter change value to determine a phase change of the target due to its relative radial velocity,

f) determining said phase change of said target proportional to its angular position off bore sight of the transmission array;

g) multiplying said filters by the conjugate of the phase shift corresponding to said filter; and

,

h) calculating the position of a true azimuth and radial velocity as a result of the determination of the change in amplitude and phase of clutter.

2. A method for locating a moving target by processing radar signals from a transmit array and dual receive arrays mounted on a moving platform in line with said platform motion relative to terrain, wherein a DPCA system is employed, said Displaced Phase Center Antenna (DPCA) system simulating an antenna to be receiving signals as if stationary while said antenna is in fact mounted on a moving carrier;

said Displaced Phase Center Antenna (DPCA) system selectively using a cancellation of clutter signals determining a target azimuth measurement from two spaced-apart array measurements of a moving target;

said method comprising the steps of;

a) transmitting signals from said transmit array toward a moving target;

b) receiving signals from said first receive array and said second receive array at delay equal D_j;

c) multiplying said received signals of said first and delayed said second receive arrays by a weighting function to reduce affects of adjacent clutter and spectral leakage of said signals;

d) calculating a correction factor of W_C and W_M for imperfections in said first array and said second array which vary with azimuth for clutter and target;

e) providing a phase correction due to inexact match of platform travel to the pulse repetition time and a phase correction for said second delay pulses in comparison with said first delay pulses and subtracting second array corresponding filters from first array filters;

f) processing data determined to be of low clutter area by measuring a phase between resultant vectors as phase proportional to radial velocity and from said azimuth of target is determined;

wherein the improvement comprises;

g) if a test for low clutter shows significant clutter is detected as in the previous paragraphs, then processing significant clutter;

h) determining whether said first array and said second array data are delayed one said data point, wherein said first array data becomes said second data point to said data point N, to said first data point, said second array data becomes said data point D+1 to said data point N, to said data point 1, to said data point D;

i) processing said data of paragraph h) as in paragraph c) to paragraph e) and multiplying said filters by the conjugate of the phase shift corresponding to the filter processed;

j) subtracting said corresponding filters of said second array from the corresponding filters of said first array and determining a result, where said target is detected at or near its peak, and solving for mover change in amplitude and phase from a first time to a second time, in said non-delayed and delayed data;

k) estimating over change in amplitude and phase from said first time to said second time from a location where said moving target is detected at its peak as a prior calculation and determining a phase correction coefficient, if said moving target is detected at its peak and solving for x, determining the location of a peak of clutter, and calculating for any estimated mover change in amplitude and phase from said first time to said second time, if said amplitude and phase is determined at said peak of target;

l) determining clutter change in amplitude and phase from said first time to said second time from the prior calculation of paragraphs “

a”

through “

k”

;

m) solving Clutter change in amplitude and phase from said first time to said second time;

n) substituting values of phase shift relative to radial

 

velocity, substituting mover weighting function in determining clutter change;

o) determining phase shift relative to radial velocity and phase shift relative to azimuth;

assuming values of clutter;

p) substituting clutter change to determine amplitude offset and phase offset;

q) measuring said phase shift relative to said radial velocity and said amplitude offset from the position of said clutter at said azimuth;

r) calculating a special filter, calculate change in

 

phase corresponding or very close to said position and insert and process at this position where X=1 at an angle equal zero;

s) performing these operations for other pairs of times, such as said second time and a third time;

t) performing these operations for other range Doppler bins where the target is detected and the results correlated;

u) correlating with performing same operations with other delay=D+1 or D−

1, and obtaining close to same results; and

,

v) correlating with other PRFs at the same antenna position.

3. A method for locating a moving target by processing radar signals from a transmit array and dual receive arrays mounted on a moving platform in line with said platform motion relative to terrain, wherein a DPCA system is employed, said Displaced Phase Center Antenna (DPCA) system simulating an antenna to be receiving signals as if stationary while said antenna is in fact mounted on a moving carrier;

said Displaced Phase Center Antenna (DPCA) system selectively using a cancellation of clutter signals determining a target azimuth measurement from two spaced-apart array measurements of a moving target;

a) transmitting signals from said transmit array toward a moving target;

b) receiving signals from said first receive array and said second receive array at delay equal D;

c) multiplying said received signals of said first and delayed said second receive arrays by a weighting function to reduce affects of adjacent clutter and spectral leakage of said signals;

d) calculating a correction factor of Wc and Wm for imperfections in said first array 1 and 2 said second array which vary with azimuth for clutter and target;

e) due to inexact match of platform travel to the pulse repetition time determining a phase correction for said second delay pulses in comparison with said first delay pulses and subtracting second array corresponding filters from first array filters;

f) processing data determined to be of low clutter area by measuring phase between resultant vectors as phase proportional to radial velocity and from that azimuth of target is determined;

wherein the improvement comprises;

g) if a test for low clutter shows significant clutter is detected as in previous paragraphs “

a”

through “

f”

, then proceeding to clutter processing;

h) said first array data and said second array data are delayed one said data point, said first array data becoming said second data point to said data point N to said first array data point, said second array data becoming said data point D+1 to said data point N, to said first data point, to said data point D;

i) processing said data of paragraph h), as in paragraph c) to paragraph e) and multiplying said filters by the conjugate of the phase shift corresponding to processed filter;

j) subtracting corresponding filters of said second array from corresponding filters of said first array and said filter where said target is detected at or near its peak, solving for Y in said non-delayed data and said delayed data where

$\begin{array}{c}Y=\left({V^{\mathrm{″<br><br>}}}_{11}-W_c<br><br>{V^{\mathrm{″<br><br>}}}_{12}\right)/\left({V^{\mathrm{\prime <br><br>}}}_{11}-W_c<br><br>{V^{\mathrm{\prime <br><br>}}}_{12}\right)\\ W_c={A_{C<br><br><br><br>M<br><br><br><br>E}}^{j<br><br>\left(\mathrm{\psi <br><br>}+K_{C<br><br><br><br>M<br><br><br><br>X}\right)}\end{array}$

k) estimating Y from the location of where said target is detected at its peak as a prior calculation illustrated in the disclosure and determining K=1 and B=0, if said target is detected at its peak K=1 and B=0 and solving for x, the location of the peak of clutter, may be calculated for any estimated Y, if Y determined at said of said peak of target, x=(angle of K₁−

Ψ

_CM)/(−

K_CM);

l) from calculation of x, determining the value of X=Ke^ja

m) from a solution in solving for X in the previous equation according to the following equation;

X=(e<sup>jDΦ

R</sup>/W_MV₁₁−

V₁₂)/(e<sup>jDΦ

R</sup>/W_MV₁₁−

V₁₂)

n) substituting all candidate Φ

_R and from which is determined Φ

_A and A_CM and Ψ

_CM for the term W_M, and where the solution is closest to the estimated value of X is the value of Φ

_R, the radial velocity and from this calculation said azimuth is calculated;

o) solving another solution for e<sup>jDΦ

R</sup>/W_M=(V″

₁₁X−

V′

₁₁)/(V″

₁₂X−

V′

₁₂)

p) substitute X in the above equation and from right side of above equation is known and made equal to DΦ

_R is determined A_CM and Ψ

_CM at the Φ

′

_A=Φ

′

_D−

Φ

′

_R where Φ

′

_A is close to the true azimuth to give a very good estimate of A_CM and Ψ

_CM;

q) A_CM and Ψ

_CM being measured from the position of clutter at said azimuth of paragraph “

p”

;

r) for the best mode, processing at peak of said clutter, at the x position of said clutter by calculating a special filter, a change in phase corresponding or very close to said position and insert and process at this position where X=1 at an angle equal zero;

s) performing these operations for other pairs of times, such as T2 and T3 and obtaining sane results therefrom;

t) performing these operations for other range Doppler bins where the target is detected and the results correlated;

u) correlating by performing said aforesaid operations with other delay=D+1 or D−

1, obtain close to same results; and

,

u) correlating with other PRFs at same antenna position, where;

V′

₁₁ Measured vector in subarray 1 at time 1 V′

₁₂ Measured vector in subarray 2 at time 1 C Clutter vector M Mover vector W_C1 Clutter weighting function for time 1 data W_M1 Mover weighting function for time 1 data Φ

_R Phase shift proportional to relative radial velocity of the mover V′

₁₁ Measured vector in subarray 1 at time 2 V′

₁₂ Measured vector in subarray 2 at time 2 X Clutter change in amplitude and phase from time 1 to time 2 Y Mover change in amplitude and phase from time 1 to time 2 W_c2-W_c Clutter weighting function for time 2 data W_M2-W_M Mover weighting function for time 2 data ψ

_CM Phase offset A_CM Amplitude offset S-FRDB fine range bin processed for clutter X Location of the peak of clutter K_CM Phase correction coefficient

4. A method for locating a moving target by processing radar signals from a transmit array and dual receive arrays mounted on a moving platform in line with said platform motion relative to terrain, wherein a DPCA system is employed, said Displaced Phase Center Antenna (DPCA) system simulating an antenna to be receiving signals as if stationary while said antenna is in fact mounted on a moving carrier;

said Displaced Phase Center Antenna (DPCA) system selectively using a cancellation of clutter signals determining a target azimuth measurement from two spaced-apart array measurements of a moving target;

said method comprising the steps of;

a) transmitting signals from said transmit array toward a moving target;

b) receiving signals from said first receive array and said second receive array at delay equal D_j;

c) multiplying said received signals of said first and delayed said second receive arrays by a weighting function to reduce affects of adjacent clutter and spectral leakage of said signals;

d) calculating a correction factor of W_C and W_M for imperfections in said first array and said second array which vary with azimuth for clutter and target;

e) providing a phase correction due to inexact match of platform travel to the pulse repetition time and a phase correction for said second delay pulses in comparison with said first delay pulses and subtracting second array corresponding filters from first array filters;

f) processing data determined to be of low clutter area by measuring a phase between resultant vectors as phase proportional to radial velocity and from said azimuth of target is determined;

wherein the improvement comprises;

g) if a test for low clutter shows significant clutter is detected as in the previous paragraphs, then processing significant clutter;

h) determining whether said first array and said second array data are delayed one said data point, wherein said first array data becomes said second data point to said data point N, to said first data point, said second array data becomes said data point D+1 to said data point N, to said data point 1, to said data point D;

i) processing said data of paragraph h) as in paragraph c) to paragraph e) and multiplying said filters by the conjugate of the phase shift corresponding to the filter processed;

j) subtracting said corresponding filters of said second array from the corresponding filters of said first array and determining a result, where said target is detected at or near its peak, and solving for mover change in amplitude and phase from a first time to a second time, in said non-delayed and delayed data;

k) estimating over change in amplitude and phase from said first time to said second time from a location where said moving target is detected at its peak as a prior calculation and determining a phase correction coefficient, if said moving target is detected at its peak and solving for x, determining the location of a peak of clutter, and calculating for any estimated mover change in amplitude and phase from said first time to said second time, if said amplitude and phase is determined at said peak of target;

l) determining clutter change in amplitude and phase from said first time to said second time from the prior calculation of paragraphs “

a”

through “

k”

;

m) solving Clutter change in amplitude and phase from said first time to said second time;

n) substituting values of phase shift relative to radial

 

velocity, substituting mover weighting function in determining clutter change;

o) determining phase shift relative to radial velocity and phase shift relative to azimuth;

assuming values of clutter;

p) substituting clutter change to determine amplitude offset and phase offset;

q) measuring said phase shift relative to said radial velocity and said amplitude offset from the position of said clutter at said azimuth;

r) calculating a special filter, calculate change in

 

phase corresponding or very close to said position and insert and process at this position where X=1 at an angle equal zero;

s) performing these operations for other pairs of times, such as said second time and a third time; and

t) performing these operations for other range Doppler bins where the target is detected and the results correlated.

5. The method of claim 4 further comprising steps:

u) correlating with performing same operations with other delay=D+1 or D−

1, and obtaining close to same results; and

v) correlating with other PRFs at the same antenna position.