Device for moving-clutter elimination in a radar

• US 4,965,585 A
• Filed: 03/08/1989
• Issued: 10/23/1990
• Est. Priority Date: 03/18/1988
• Status: Expired due to Fees

• Current Assignee: Thomson-CSF
• Original Assignee: Thomson-CSF
• Inventors: Lepere, Guy, Coulmier, Jean-Pol, Kunegel, Jacques
• Primary Examiner(s): Barron, Jr., Gilberto
• Application Number:
  US07/321,420
• Time in Patent Office: 594 Days
• Field of Search: 342/159, 342/160, 342/162
• US Class Current: 342/160
• CPC Class Codes: G01S 13/524 based upon the phase or frequency shift resulting from movement of objects, with reference to the transmitted signals, e.g. coherent MTi

Abstract

The invention resides in the fact that the moving-clutter elimination filter is composed of several transversal filters whose n+1 multiplying coefficients K0, K1, . . . , Kα, . . . , Kn are fixed and are derived from the coefficients A0, A1, . . . , Aα, . . . , An of the fixed-clutter elimination filter by multiplying the latter by the factors:

Fα=e.sup.j2πFd×Tr(n-α).

Claims

1. A device for eliminating the moving clutter with a Doppler shift Fd in a coherent pulse Doppler radar with pulse repetition frequency Fr comprising:

a first processing channel having a fixed-clutter elimination transversal filter using (n+1) first multiplication coefficients A0, A1, . . . , Aα

, . . . , An followed by a threshold circuit;

a second processing channel having only a threshold circuit;

a third processing channel having a moving-clutter elimination transversal filter, said transversal filter comprising a bank of multiplying circuits having a set of fixed second multiplication coefficients K or K'"'"' which are derived from the first multiplication coefficients A0, A1, . . . , Aα

, . . . , An of said fixed-clutter elimination transversal filter in said first processing channel by multiplying the first multiplication coefficients A0, A1, . . . , Aα

, . . . , An by a factor Fα

;

space="preserve" listing-type="equation">Fα

=e.sup.j2π

Fd×

Tr(n-α

),

where Tr is a pulse repetition period, n is one less than the number of first multiplication coefficients A0, A1, . . . , Aα

, . . . , An, and α

is an order of a particular first multiplication coefficient A0, A1, . . . , Aα

, . . . , An; and

an OR circuit, coupled to receive said first, second, and third processing channel, having an output indicative of a processed signal.

2. A device for eliminating the moving clutter with a Doppler shift Fd in a coherent pulse Doppler radar with pulse repetition frequency Fr comprising:

a first processing channel having a fixed-clutter elimination transversal filter using (n+1) first multiplication coefficients A0, A1, . . . , Aα

, . . . , An followed by a threshold circuit;

a second processing channel having only a threshold circuit;

a third processing channel having a moving-clutter elimination transversal filter, said transversal filter comprising a bank of multiplying circuits having a set of fixed second multiplication coefficients K or K'"'"' which are derived from the first multiplication coefficients A0, A1, . . . , Aα

, . . . , An of said fixed-clutter elimination transversal filter in said first processing channel by multiplying the first multiplication coefficients A0, A1, . . . , Aα

, . . . , An by a factor Fα

;

space="preserve" listing-type="equation">Fα

=e.sup.j2π

Fd×

Tr(n-1).

where Tr is a pulse repetition period, n is one less than the number of the first multiplication coefficients A0, A1, . . . , Aα

, . . . , An, and α

is an order of a particular first multiplication coefficient A0, A1, . . . , Aα

, . . . , An; and

an OR circuit, coupled to receive said first, second, and third processing channel, having an output indicative of a processed signal;

wherein said device is intended for filtering a complex signal I+jQ whose components are obtained in the form of successive digital codes separated by time intervals equalling the pulse repetition period Tr, said moving-clutter elimination transversal filter using, at a frequency +Fr/4, four second multiplication coefficients K0, K1, K2, K3 that may respectively have the values of one of the four following sets;

space="preserve" listing-type="equation">(-j, 3, 3j, -1)

space="preserve" listing-type="equation">(1, 3j, -3, -j)

space="preserve" listing-type="equation">(j, -3, -3j,

     1)

space="preserve" listing-type="equation">(-1, -3j, 3, j)

and, at a frequency -Fr/4, four second multiplication coefficients K'"'"'0, K'"'"'1, K'"'"'2, K'"'"'3 that may respectively have the values of one of the four following sets;

space="preserve" listing-type="equation">(j, 3, -3j, -1)

space="preserve" listing-type="equation">(1, 3j, -3, j)

space="preserve" listing-type="equation">(-j, -3, -3j,

     1)

space="preserve" listing-type="equation">(-1, 3j, 3, -j)

wherein said moving-clutter elimination transversal filter comprises;

a fourth processing channel for processing the successive codes of the real component I;

a fifth processing channel for processing the successive codes of the imaginary component Q;

wherein each said first and second channel include three memories to store all the successive codes appearing during the pulse repetition period Tr, thereby enabling a simultaneous reading of codes I0 or Q0, I1 or Q1 or Q1, I2 or Q2, I3 or Q3 corresponding to the same signal to be filtered;

a plurality of adder circuits, connected to be supplied with the radar signals I0 through I3 and Q0 through Q3 delivered respectively by the first and second processing channels, for computing, by use of the modulus of one of said sets of coefficients, the real and imaginary parts of a filtered signal corresponding to the shift +Fr/4, and of a filtered signal corresponding to the shift -Fr/4; and

a plurality of circuits for computing the modulus of said filtered signals.

3. A device according to claim 2, wherein said plurality of adder circuits are provided for computing the following sums:

-I3+3I-Q0+3Q2, that corresponds to the real part of the filter output signal shifted by +Fr/4;

-Q3+3Q1+I0-3I2, that corresponds to the imaginary part of the filter output signal shifted by +Fr/4;

-I3+3I1+Q0-3Q2, that corresponds to the real part of the output filter signal shifted by -Fr/4; and

-Q3+3Q1-10+3I2 that corresponds to the imaginary part of the filter output signal shifted by -Fr/4.

4. A device for eliminating the moving clutter with a Doppler shift Fd in a coherent pulse Doppler radar with pulse repetition frequency Fr comprising:

a first processing channel having a fixed-clutter elimination transversal filter using (n+1) first multiplication coefficients A0, A1, . . . , Aα

, . . . , An followed by a threshold circuit;

a second processing channel having only a threshold circuit;

a third processing channel having a moving-clutter elimination transversal filter, said transversal filter comprising a bank of multiplying circuits having a set of fixed second multiplication coefficients K or K'"'"' which are derived from the first multiplication coefficients A0, A1, . . . , Aα

, . . . , An of said fixed-clutter elimination transversal filter in said first processing channel by multiplying the first multiplication coefficients A0, A1, . . . , Aα

, . . . , An by a factor Fα

;

space="preserve" listing-type="equation">Fα

=e.sup.j2π

Fd×

Tr(n-α

),

where Tr is a pulse repetition period, n is one less than the number of the first multiplication coefficients A0, A1, . . . , Aα

, . . . , An, and α

is an order of a particular first multiplication coefficient A0, A1, . . . , Aα

, . . . , An; and

an OR circuit, coupled to receive said first, second, and third processing channel, having an output indicative of a processed signal;

wherein said pulse repetition frequency Fr of transmitted radar pulses is wobulated;

wherein at least said moving-clutter elimination transversal filter in said third channel is preceded by a wobulation compensating device that includes a multiplying circuit which multiplies the radar signal by a coefficient Wi such that;

space="preserve" listing-type="equation">Wi=e.sup.j2π

Ti×

Fr,

where Ti is a pulse repetition period when the repetition frequency of the transmitted radar pulses is wobulated.

5. A device for eliminating the moving clutter with a Doppler shift Fd in a coherent pulse Doppler radar with pulse repetition frequency Fr comprising:

a first processing channel having a fixed-clutter elimination transversal filter using (n+1) first multiplication coefficients A0, A1, . . . , Aα

, . . . , An followed by a threshold circuit;

a second processing channel having only a threshold circuit;

a third processing channel having a moving-clutter elimination transversal filter, said transversal filter comprising a bank of multiplying circuits having a set of fixed second multiplication coefficients K or K'"'"' which are derived from the first multiplication coefficients A0, A1, . . . , Aα

, . . . , An of said fixed-clutter elimination transversal filter in said first processing channel by multiplying the first multiplication coefficients A0, A1, . . . , Aα

, . . . , An by a factor Fα

;

space="preserve" listing-type="equation">Fα

=e.sup.j2π

Fd×

Tr(n-α

),

where Tr is a pulse repetition period, n is one less than the number of the first multiplication coefficients A0, A1, . . . , Aα

, . . . , An, and α

is an order of a particular first multiplication coefficient A0, A1, . . . , Aα

, . . . , An; and

an OR circuit, coupled to receive said first, second, and third processing channel, having an output indicative of a processed signal;

wherein said processing channels are preceded by a fixed-clutter elimination transversal filter.

6. A device for eliminating the moving clutter with a Doppler shift Fd in a coherent pulse Doppler radar with pulse repetition frequency Fr comprising:

a first processing channel having a fixed-clutter elimination transversal filter using (n+1) first multiplication coefficients A0, A1, . . . , Aα

, . . . , An followed by a threshold circuit;

a second processing channel having only a threshold circuit;

a third processing channel having a moving-clutter elimination transversal filter, said transversal filter comprising a bank of multiplying circuits having a set of fixed second multiplication coefficients K or K'"'"' which are derived from the first multiplication coefficients A0, A1, . . . , Aα

, . . . , An of said fixed-clutter elimination transversal filter in said first processing channel by multiplying the first multiplication coefficients A0, A1, . . . , Aα

, . . . , An by a factor Fα

;

space="preserve" listing-type="equation">Fα

=e.sup.j2π

Fd×

Tr(n-α

),

where Tr is a pulse repetition period, n is one less than the number of the first multiplication coefficients A0, A1, . . . , Aα

, . . . , An, and α

is an order of a particular first multiplication coefficient A0, A1, . . . , Aα

, . . . , An; and

an OR circuit, coupled to receive said first, second, and third processing channel, having an output indicative of a processed signal;

wherein said moving-clutter elimination transversal filter is at a frequency +Fr/4 and uses four second multiplication coefficients K0, K1, K2, K3 that may respectively have the values of one of the four following sets;

space="preserve" listing-type="equation">(-j, 3, 3j, -1)

space="preserve" listing-type="equation">(1, 3j, -3, -j)

space="preserve" listing-type="equation">(j, -3, -3j,

     1)

space="preserve" listing-type="equation">(-1, -3j, 3, j).

7. A device for eliminating the moving clutter with a Doppler shift Fd in a coherent pulse Doppler radar with pulse repetition frequency Fr comprising:

a first processing channel having a fixed-clutter elimination transversal filter using (n+1) first multiplication coefficients A0, A1, . . . , Aα

, . . . , An followed by a threshold circuit;

a second processing channel having only a threshold circuit;

a third processing channel having a moving-clutter elimination transversal filter, said transversal filter comprising a bank of multiplying circuits having a set of fixed second multiplication coefficients K or K'"'"' which are derived from the first multiplication coefficients A0, A1, . . . , Aα

, . . . , An of said fixed-clutter elimination transversal filter in said first processing channel by multiplying the first multiplication coefficients A0, A1, . . . , Aα

, . . . , An by a factor Fα

;

space="preserve" listing-type="equation">Fα

=e.sup.j2π

Fd×

Tr(n-α

),

where Tr is a pulse repetition period, n is one less than the number of the first multiplication coefficients A0, A1, . . . , Aα

, . . . , An, and α

is an order of a particular first multiplication coefficient A0, A1, . . . , Aα

, . . . , An; and

an OR circuit, coupled to receive said first, second, and third processing channel, having an output indicative of a processed signal;

wherein said moving-clutter elimination transversal filter is at a frequency -Fr/4 and uses four second multiplication coefficients K0, K1, K2, K3 that may respectively have the values of one of the four following sets;

space="preserve" listing-type="equation">(j, 3, -3j, -1)

space="preserve" listing-type="equation">(1, 3j, -3, j)

space="preserve" listing-type="equation">(-j, -3, -3j,

     1)

space="preserve" listing-type="equation">(-1, 3j, 3, -j).