Side lobe suppression

• US 8,115,679 B2
• Filed: 02/05/2009
• Issued: 02/14/2012
• Est. Priority Date: 02/07/2008
• Status: Active Grant

• Current Assignee: Saab AB
• Original Assignee: Saab AB
• Inventors: Falk, Kent
• Primary Examiner(s): Tarcza, Thomas
• Assistant Examiner(s): Mull, Fred H
• Application Number:
  US12/366,335
• Publication Number:
  US 20090256749A1
• Time in Patent Office: 1,104 Days
• Field of Search: 342379-380, 342/383, 367/905
• US Class Current: 342/380
• CPC Class Codes: G01S 7/2813 Means providing a modification of the radiation pattern for cancelling noise, clutter or interfering signals, e.g. side lobe suppression, side lobe blanking, null-steering arrays specially adapted to secondary radar systems G01S13/762; aerials or aerials systems H01Q21/29, H01Q25/00
• CPC Class Codes: H01Q 3/2635 the auxiliary unit being composed of a plurality of antennas

Abstract

Embodiments include a method to suppress side lobes of a main antenna by creating cancellation directions using a Side Lobe Canceller (SLC). Various embodiments also provide the Side Lobe Canceller.

Claims

1. A method to suppress side lobes of a main antenna using a side lobe canceller (SLC), the SLC comprising an auxiliary antenna and an Adaptive Side lobe Canceller control unit (ASC), the auxiliary antenna having N antenna elements, where the antenna element may also be a sub array, 1 to N, N being ≧

1, and a feedback loop from an output terminal of the SLC to the ASC, the method comprising;

using the ASC, receiving a main antenna output waveform from the main antenna;

using the ASC, receiving auxiliary antenna output waveforms s₁to s_N from the respective antenna elements or sub arrays of the auxiliary antenna;

transforming the auxiliary antenna output waveforms using respective transforming units Tr₁ to Tr_N to provide transformed auxiliary antenna output waveforms;

delaying the main antenna output waveform to provide a delayed output waveform of the main antenna; and

calculating a respective weighting function W(ω

) for Q spectral components indexed by an integer q ranging from 0 to Q−

1, the Q spectral components obtained via dividing a bandwidth B into Q components for each antenna element or sub array, the respective weighting function W(ω

) calculated using a criterion to minimize a jamming influence on a side-lobe-suppressed main antenna output waveform from the SLC; and

wherein the transforming the auxiliary antenna output waveforms includes using one or more control parameters calculated from the respective weighting function W(ω

) at discrete angular frequencies ω

_q using the ASC; and

wherein, using the ASC, the one or more control parameters are calculated on a recurring basis and provided via respective control signals c₁ to C_N for use in transforming the auxiliary antenna output waveforms; and

wherein the method includes subtracting the transformed auxiliary antenna output waveforms in the time or frequency domain from the delayed output waveform of the main antenna to provide the side-lobe-suppressed main antenna output waveform from the SLC having reduced jamming influence over the bandwidth B.

2. The method of claim 1, wherein the weighting function is W(ω

)=A(ω

)·

e<sup>−

j·

ω

·

τ

(ω

)</sup> or W(ω

)=A(ω

)·

e<sup>−

·

φ

(ω

)</sup>.

3. The method of claim 1, wherein the criterion to minimize the jamming influence includes minimizing an output residual power of the side-lobe-suppressed main antenna output waveform.

4. The method of claim 1, comprising:

for each row n of an S matrix, on a recurring basis, Fourier transforming (FT) the main antenna output waveform to calculate a row vector S_M including elements S_SMq(q ε

[0. . . Q−

1]) and applying a delay compensation to the row vector S_M;

on a recurring basis, calculating a W matrix including elements W_n,q(nε

[1. . . N],qε

[0. . . Q−

1]) including minimizing an output residual power of the side-lobe-suppressed main antenna output waveform according to a relation P=E[|Z|²]=E[|S_M^T−

W^T·

S|²]; and

wherein calculating the control signals c₁ to c_N on a recurring basis includes inverse-Fourier transforming rows 1 to N of the W matrix and using these rows as control signals when a time domain realization is used, or using the row 1 to N of the W matrix as the control signals C₁ to c_Nwhen a frequency domain realization is used.

5. The method of claim 1, comprising feeding transformed auxiliary antenna output waveforms S₁′

to s_N′

to a Cancellation Network (CN) via a first summation network.

6. The method of claim 1, comprising Fourier transforming respective auxiliary antenna output waveforms s_in(t) via respective transforming units to provide respective sets of Q spectral components, 0 to (Q−

1), each spectral component having a center frequency f_q, and frequency dependent parameters time delay τ

_n,q or phase shift φ

_n,q applied to each spectral component q;

applying an amplification or attenuation factor, a_n,q, to each spectral component q; and

inverse Fourier transforming (IFT) respective sets of Q spectral components via respective transforming units back into the time domain to provide respective output waveforms s_out(t) from each transforming unit.

7. The method of claim 1, comprising:

successively time delaying auxiliary antenna output waveforms s_in(m·

T) via respective transforming units in Q−

1 time steps T, from 1 to Q−

1 to provide time delayed copies of the auxiliary antenna output waveform s_in(m·

T);

calculating, via respective transforming units, Q parameters comprising weighting coefficients w_n,0 to w<sub>n,Q−

l</sub> for antenna element n, identified with two indexes, the first corresponding to the antenna element number, and the second corresponding to a consecutive number q representing a spectral component and ranging from 0 to Q−

1, the Q parameters comprising weighting coefficients w_n,0 to w<sub>n,Q−

1</sub> calculated via inverse Fourier transforming (IFT) W(ω

)=A(ω

)·

e<sup>−

j·

ω

·

τ

(ω

)</sup> for the Q spectral components q, resulting from dividing the bandwidth B in Q components, the calculation being performed for each antenna element or sub array (A₁−

A_N) by minimizing the jamming influence on the side-lobe-suppressed main antenna output waveform at a center frequency f_q of each spectral component q; and

multiplying, via respective transforming units, the auxiliary antenna output waveform s_in(m·

T) with the first weighting coefficient w_n,0;

successively multiplying, via respective transforming units, respective time delayed copies of the auxiliary antenna output waveform with the weighting coefficient having the same second index as the number of time step delays T included in the time delayed copy of the auxiliary antenna output waveform; and

summing, via respective transforming units, the result of each multiplication to provide an output waveform s_out(m·

T) from each transforming unit.

8. The method of claim 7, comprising reducing a number of operations to less than Q operations via (1) setting the first x weighting coefficients and the last y weighting coefficients in the series of weighting coefficients w_n,0 to w_n,Q−

1 to zero, (2) integrating the first x time delays T into a time delay D, equal to x·

T, and (3) excluding the last y multiplications.

9. The method of claim 1, wherein the transformer units include an analog transforming unit.

10. The method of claim 1, comprising using Q single spectral first summation networks, one for each spectral component from the antenna elements in the auxiliary antenna and Q single spectral Cancellation Networks (CN) where each spectral component of the delayed output waveform of the main antenna is subtracted from the corresponding spectral component from the auxiliary antenna summed in the respective single spectral first summation network;

and

inverse Fourier transforming (IFT) the waveforms of the resulting spectral components to provide the side-lobe-suppressed main antenna output waveform.

11. A Side Lobe Canceller (SLC) comprising an auxiliary antenna and an Adaptive Side lobe Canceller control unit (ASC), the auxiliary antenna having N antenna elements , where the antenna elements may also be a sub array, 1 to N, N being ≧

1, and a feedback loop from an output terminal of the SLC to the ASC, the SLC configured to;

receive a main antenna output waveform from a main antenna using the ASC;

receive auxiliary antenna output waveforms s₁to s_N from the respective antenna elements or sub arrays of the auxiliary antenna using the ASC;

delay the main antenna output waveform to provide a delayed output waveform of the main antenna; and

calculate a respective weighting function W(ω

) for Q spectral components indexed by an integer q ranging from 0 to Q−

1, the Q spectral components obtained via dividing a bandwidth B into Q components for each antenna element or sub array, the respective weighting function W(ω

) calculated using a criterion to minimize a jamming influence on a side-lobe-suppressed main antenna output waveform from the SLC;

transform the auxiliary antenna output waveform using respective transforming units Tr₁ to Tr_N to provide transformed auxiliary antenna output waveforms, the transforming units configured to use one or more control parameters calculated from the respective weighting function W(ω

) at discrete angular frequencies ω

_q, wherein each output waveform S₁ to S_N from the antenna elements or sub arrays of the auxiliary antenna is provided to the transforming units Tr₁ to Tr_N;

calculate control parameters on a recurring basis;

provide the calculated control parameters to the respective transforming units via respective control signals c₁ to c_N for use in transforming the auxiliary antenna output waveforms; and

subtract the transformed auxiliary antenna output waveforms in the time or frequency domain from the delayed output waveform of the main antenna to provide the side-lobe-suppressed main antenna output waveform from the SLC having reduced jamming influence over the bandwidth B.

12. The SLC of claim 11, wherein the weighting function is W(ω

)=A(ω

)·

e<sup>−

j·

ω

·

τ

(ω

)</sup> or W(ω

)=A(ω

)·

e<sup>−

j·

φ

(ω

)</sup>.

13. The SLC of claim 11, wherein the criterion to minimize the jamming influence includes minimizing an output residual power of the side-lobe-suppressed main antenna output waveform.

14. The SLC of claim 11, wherein, the SLC is configured on a recurring basis to:

Fourier transform (FT), for each row n of an S matrix, the main antenna output waveform to calculate a row vector S_M including elements S_Mq (qε

[0. . . Q−

1]) and apply a delay compensation to the row vector S_M;

calculate a W matrix including elements W_n,q(nε

[1. . . N],qε

[0. . . Q−

1]) including minimizing an output residual power of the side-lobe-suppressed main antenna output waveform according to a relation P=E[|Z|²]=E[|S_M^T−

W^T·

S|²]; and

calculate the control signals c₁ to C_N, via inverse-Fourier transforming (IFT) rows 1to N of the W matrix and using these rows as control signals when a time domain realization is used, or using the row 1to N of the W matrix as the control signals c₁ to c_N when a frequency domain realization is used.

15. The SLC of claim 11, wherein the SLC is configured to provide transformed auxiliary antenna output waveforms s₁′

to s_N′

to a Cancellation Network (CN) via a first summation network.

16. The SLC of claim 11, wherein the respective transforming units comprise Fourier transforming (FT) units configured to FT respective auxiliary antenna output waveforms s_in(t) to provide respective sets of Q spectral components, 0 to (Q−

1), each spectral component having a center frequency f_q, and frequency dependent parameters time delay τ

_n,q or phase shift φ

_n,q applied to each spectral component q; and

wherein the SLC is configured to apply an amplification or attenuation factor, a_{n, q}, to each spectral component q; and

wherein the respective transforming units comprise Inverse Fourier transforming (IFT) units configured to inverse Fourier transform (IFT) respective sets of Q spectral components back into the time domain to provide respective output waveforms s_out(t) from each transforming unit.

17. The SLC of claim 11, wherein the SLC is configured to:

successively time delay auxiliary antenna output waveforms s_in(m·

T) via respective transforming units in Q−

1 time steps T, from 1 to Q−

1 to provide time delayed copies of the auxiliary antenna output waveform s_in(m·

T);

calculate, via respective transforming units, Q parameters comprising weighting coefficients w_n,0 to w<sub>n,Q−

1</sub> for antenna element n, identified with two indexes the first corresponding to the antenna element number and the second corresponding to a consecutive number q representing a spectral component and ranging from 0 to Q−

1, the SLC configured to calculate Q parameters comprising the weighting coefficients w_n,0 to w<sub>n,Q−

1</sub> via inverse Fourier transformation (IFT) of W(ω

)=A(ω

)·

e<sup>−

j·

ω

·

τ

(ω

)</sup> for the Q spectral components q, resulting from dividing the bandwidth B in Q components, the calculation being performed for each antenna element or sub array (A₁−

A_N) by minimizing the jamming influence on the side-lobe-suppressed main antenna output waveform at a center frequency f_q of each spectral component q; and

multiply, via respective transforming units, the auxiliary antenna output waveform s_in(m·

T) with the first weighting coefficient w_{n ,0};

successively multiply, via respective transforming units, respective time delayed copies of the auxiliary antenna output waveform with the weighting coefficient having the same second index as the number of time step delays T included in the time delayed copy of the auxiliary antenna output waveform; and

sum, via respective transforming units, the result of each multiplication to provide an output waveform s_out(m·

T) from each transforming unit.

18. The SLC of claim 17, wherein the SLC is configured to reduce a number of operations to less than Q operations via (1) setting the first x weighting coefficients and the last y weighting coefficients in the series of weighting coefficients w_n,0 to w_n,Q−

1 to zero, (2) integrating the first x time delays T into a time delay D, equal to x·

T, and (3) excluding the last y multiplications.

19. The SLC of claim 11, wherein the transformer units include an analog transforming unit.

20. The SLC of claim 11, comprising Q single spectral first summation networks, one for each spectral component from the antenna elements in the auxiliary antenna and Q single spectral Cancellation Networks (CN);

and

wherein the SLC is configured to subtract each spectral component of the delayed output waveform of the main antenna from the corresponding spectral component from the auxiliary antenna summed in the respective single spectral first summation network; and

wherein the SLC is configured to inverse Fourier transform (IFT) the waveforms of the resulting spectral components to provide the side-lobe-suppressed main antenna output waveform.

21. A method to suppress side lobes of a main antenna using a side lobe canceller (SLC), the SLC comprising an auxiliary antenna and an Adaptive Side lobe Canceller control unit (ASC), the auxiliary antenna having N antenna elements, where the antenna element may also be a sub array, 1 to N, N being ≧

1, and a feedback loop from an output terminal of the SLC to the ASC, the method comprising;

using the ASC, receiving a main antenna output waveform from the main antenna;

using the ASC, receiving auxiliary antenna output waveforms s₁ to s_N from the respective antenna elements or sub arrays of the auxiliary antenna;

transforming the auxiliary antenna output waveforms using respective transforming units Tr₁ to Tr_N to provide transformed auxiliary antenna output waveforms;

delaying the main antenna output waveform to provide a delayed output waveform of the main antenna; and

calculating a respective weighting function W(ω

) for Q spectral components indexed by an integer q ranging from 0 to Q−

1, the Q spectral components obtained via dividing a bandwidth B into Q components for each antenna element or sub array, the respective weighting function W(ω

) calculated using a criterion to minimize a jamming influence on a side-lobe-suppressed main antenna output waveform from the SLC, wherein the criterion to minimize the jamming influence includes minimizing an output residual power of the side-lobe-suppressed main antenna output waveform,

wherein the transforming the auxiliary antenna output waveforms includes using one or more control parameters calculated from the respective weighting function W(ω

) at discrete angular frequencies ω

_q using the ASC; and

wherein, using the ASC, the one or more control parameters are calculated on a recurring basis and provided via respective control signals c₁ to c_N for use in transforming the auxiliary antenna output waveforms; and

wherein the method includes subtracting the transformed auxiliary antenna output waveforms in the time or frequency domain from the delayed output waveform of the main antenna to provide the side-lobe-suppressed main antenna output waveform from the SLC having reduced jamming influence over the bandwidth B,

and further including;

successively time delaying auxiliary antenna output waveforms s_in(m·

T) via respective transforming units in Q−

1 time steps T, from 1 to Q−

1 to provide time delayed copies of the auxiliary antenna output waveform s_in(m·

T);

calculating, via respective transforming units, Q parameters comprising weighting coefficients w_n,0 to w<sub>n,Q−

1</sub> for antenna element n, identified with two indexes, the first corresponding to the antenna element number, and the second corresponding to a consecutive number q representing a spectral component and ranging from 0 to Q−

1, the Q parameters comprising weighting coefficients w_n,0 to w<sub>n,Q−

1</sub> calculated via inverse Fourier transforming (IFT) W(ω

)=A(ω

)·

e<sup>−

j·

ω

·

τ

(ω

)</sup> for the Q spectral components q, resulting from dividing the bandwidth B in Q components, the calculation being performed for each antenna element or sub array (A₁−

A_N) by minimizing the jamming influence on the side-lobe-suppressed main antenna output waveform at a center frequency f_q of each spectral component q; and

multiplying, via respective transforming units, the auxiliary antenna output waveform s_in(m·

T) with the first weighting coefficient w_n,0;

successively multiplying, via respective transforming units, respective time delayed copies of the auxiliary antenna output waveform with the weighting coefficient having the same second index as the number of time step delays T included in the time delayed copy of the auxiliary antenna output waveform; and

summing, via respective transforming units, the result of each multiplication to provide an output waveform s_out(m·

T) from each transforming unit, and

reducing a number of operations to less than Q operations via (1) setting the first x weighting coefficients and the last y weighting coefficients in the series of weighting coefficients w_n,0 to w<sub>n,Q−

1</sub> to zero, (2) integrating the first x time delays T into a time delay D, equal to x·

T, and (3) excluding the last y multiplications.

22. A Side Lobe Canceller (SLC) comprising an auxiliary antenna and an Adaptive Side lobe Canceller control unit (ASC), the auxiliary antenna having N antenna elements, where the antenna elements may also be a sub array, 1 to N, N being ≧

1, and a feedback loop from an output terminal of the SLC to the ASC, the SLC configured to;

receive a main antenna output waveform from a main antenna using the ASC;

receive auxiliary antenna output waveforms s₁ to s_N from the respective antenna elements or sub arrays of the auxiliary antenna using the ASC;

delay the main antenna output waveform to provide a delayed output waveform of the main antenna; and

calculate a respective weighting function W(ω

) for Q spectral components indexed by an integer q ranging from 0 to Q−

1, the Q spectral components obtained via dividing a bandwidth B into Q components for each antenna element or sub array, the respective weighting function W(ω

) calculated using a criterion to minimize a jamming influence on a side-lobe-suppressed main antenna output waveform from the SLC, wherein the criterion to minimize the jamming influence includes minimizing an output residual power of the side-lobe-suppressed main antenna output waveform;

transform the auxiliary antenna output waveform using respective transforming units Tr₁ to Tr_N to provide transformed auxiliary antenna output waveforms, the transforming units configured to use one or more control parameters calculated from the respective weighting function W(ω

) at discrete angular frequencies ω

_q, wherein each output waveform s₁ to s_N from the antenna elements or sub arrays of the auxiliary antenna is provided to the transforming units Tr_l to Tr_N;

calculate control parameters on a recurring basis;

provide the calculated control parameters to the respective transforming units via respective control signals C₁ to C_N, for use in transforming the auxiliary antenna output waveforms; and

subtract the transformed auxiliary antenna output waveforms in the time or frequency domain from the delayed output waveform of the main antenna to provide the side-lobe-suppressed main antenna output waveform from the SLC having reduced jamming influence over the bandwidth B;

successively time delay auxiliary antenna output waveforms s_in(m·

T) via respective transforming units in Q−

1 time steps T, from 1 to Q−

1 to provide time delayed copies of the auxiliary antenna output waveform s_in(m·

T);

calculate, via respective transforming units, Q parameters comprising weighting coefficients w_n,0 to w<sub>n,Q−

1</sub> for antenna element n, identified with two indexes the first corresponding to the antenna element number and the second corresponding to a consecutive number q representing a spectral component and ranging from 0 to Q−

1, the SLC configured to calculate Q parameters comprising the weighting coefficients w_n,0 to w<sub>n,Q−

1</sub> via inverse Fourier transformation (IFT) of W(ω

)=A(ω

)·

e<sup>−

j·

ω

·

τ

(ω

)</sup> for the Q spectral components q, resulting from dividing the bandwidth B in Q components, the calculation being performed for each antenna element or sub array (A₁−

A_N) by minimizing the jamming influence on the side-lobe-suppressed main antenna output waveform at a center frequency f_q of each spectral component q; and

multiply, via respective transforming units, the auxiliary antenna output waveform s_in(m·

T) with the first weighting coefficient w_n,0;

successively multiply, via respective transforming units, respective time delayed copies of the auxiliary antenna output waveform with the weighting coefficient having the same second index as the number of time step delays T included in the time delayed copy of the auxiliary antenna output waveform; and

sum, via respective transforming units, the result of each multiplication to provide an output waveform s_out(m·

T) from each transforming unit,

wherein the SLC is configured to reduce a number of operations to less than Q operations via (1) setting the first x weighting coefficients and the last y weighting coefficients in the series of weighting coefficients w_n,0 to w<sub>n,Q−

1</sub> to zero, (2) integrating the first x time delays T into a time delay D, equal to x·

T, and (3) excluding the last y multiplications.