Monopulse signal processor and method using same

• US 5,576,711 A
• Filed: 10/17/1984
• Issued: 11/19/1996
• Est. Priority Date: 10/17/1984
• Status: Expired due to Term

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Martin Marietta Corporation
• Inventors: Berkowitz, Raymond S., Morris, Randall D.
• Primary Examiner(s): Cangialosi, Salvatore
• Application Number:
  US06/661,795
• Time in Patent Office: 4,416 Days
• Field of Search: 343/5 NQ, 343/16 M, 343/427, 364/517, 342/152
• US Class Current: 342/152
• CPC Class Codes: G01S 13/44 Monopulse radar, i.e. simultaneous lobing
• CPC Class Codes: G01S 7/2926 by integration

Abstract

A monopulse signal processor provides target monopulse ratios and thus target angles having an improved accuracy in those situations where a low signal-to-noise ratio subsists and the monopulse ratio is derived from a sequence of pulses. The monopulse ratio value is determined by: ##EQU1## and Σ_Ii is the in-phase component of the sum signal for the i^th pulse, Σ_Qi is the quadrature component of the sum signal for the i^th pulse, Δ_Ii is the in-phase component of the difference signal for the i^th pulse, and Δ.sub.Ωi is the quadrature component of the difference signal for the i^th pulse.

Claims

1. In a monopulse signal processing system of the type which receives an in-phase difference signal (Δ

_I) and a quadrature difference signal (Δ

_Q) in a first coordinate and an in-phase sum signal (Σ

_I) and a quadrature sum signal (Σ

_Q), all derived from an antenna system and which provides target tracking information with respect to a target which is a source of at least some of the energy in said received signals and in the process converts each of said received signals to a series of digital signals, each representative of an instantaneous amplitude of that received signal and derives from those digital signals a first monopulse ratio signal which corresponds to the angle in said first coordinate between the receive beam axis of said antenna system and a line to said target, and said system is of the type which includes means responsive to said Σ

_I and Σ

_Q digital signals for providing a digital signal α

which is the sum of their squares (Σ

_I² +Σ

_Q²), means responsive to said Σ

_I, Σ

_Q, Δ

_I and Δ

_Q digital signals for providing a digital signal γ

which is the sum of the product of said Σ

_I and Δ

_I signals and the product of said Σ

_Q and Δ

_Q signals (Σ

_I Δ

_I +Σ

_Q Δ

_Q), the improvement comprising;

means responsive to said Δ

_I and Δ

_Q digital signals for providing a digital signal β

which is the sum of their squares (Δ

_I² +Δ

_Q²); and

means for deriving said first monopulse ratio signal from said α

, β and

γ

digital signals.

2. The improvement recited in claim 1 wherein said means for deriving includes:

means responsive to said α and

β

digital signals for providing a digital signal η

which is their difference (β

-α

);

means responsive to said η

signal for providing a signal η

² ;

means responsive to said γ

digital signal for providing a digital signal 2γ and

a digital signal 4γ

² ;

means responsive to said η

² and 4γ

² digital signals for providing a digital signal which is the square root of their sum (√

η

² +4γ

² );

means responsive to said √

η

² +4γ

² digital signal and said η

digital signal for providing a digital signal which is their sum (η

+√

η

² +4γ

² ); and

means responsive to said (η

+√

η

² +4γ

² ) digital signal and said 2γ

digital signal for providing a digital signal ρ

whose value is (η

+√

η

² +4γ

² ) divided by 2γ

, said ρ

signal being provided as said first monopulse ratio signal.

3. The improvement recited in claim 2 wherein:

said means responsive to said η

signal comprises a first accumulating adder means responsive to said η

signal for each of N pulses for providing a signal η

_T which is their sum;

said means responsive to said γ

signal comprises a second accumulating adder means responsive to said 2γ

signal for each of said N pulses for providing a signal γ

_T which is their sum, whereby said target angle signal depends on the received signals from said N pulses.

4. The improvement recited in claim 3 wherein said processing system also includes:

means for converting said monopulse ratio signal into a target angle signal specifying said corresponding angle.

5. The improvement recited in claim 2 wherein said processing system also includes:

means for receiving in-phase and quadrature difference signals in a second co-ordinate;

means responsive to said second co-ordinate signals for deriving a second monopulse ratio signal, which corresponds to the angle in said second co-ordinate between said receive beam axis and said line to said target; and

means for providing said second monopulse ratio signal at an output.

6. The improvement recited in claim 2 further comprising means for comparing said 4γ

² signal with a threshold value and means for providing a monopulse ratio signal equal to γ

/α

whenever said 4γ

² signal is less than said threshold value.

7. A monopulse method of processing received radio signals to provide a signal ρ

which is a measure of the angle in a first coordinate between the receive beam axis of an antenna and a line to a target from which the antenna receives energy, said method comprising the steps of;

(a) processing signals received from said antenna to provide digital signals representative of the instantaneous amplitudes of in-phase and quadrature difference signals (Δ

_I and Δ

_Q, respectively) in said first coordinate and in-phase and quadrature sum signals (Σ

_I and Σ

_Q, respectively);

(b) squaring said Σ

_I, Σ

_Q, Δ

_I and Δ

_Q signals and adding them to provide a digital signal η

equal to Δ

_I² +Δ

_Q² -Σ

_I² -Σ

_Q² ;

(c) multiplying said Σ

_I signal by 2 times said Δ

_I signal and said Σ

_Q signal by 2 times said Δ

_Q signal and adding them to provide a digital signal 2γ

equal to 2Σ

_I Δ

_I +2Σ

_Q Δ

_Q ; and

(d) squaring said η and

2γ

signals and adding them to provide a signal equal to √

η

² +4γ

² ; and

(e) extracting the square root √

η

² +4γ

²

(f) adding η

to said square root and dividing by 2γ

to provide a signal equal to ##EQU14## as said ρ

signal.

8. The method recited in claim 7 further comprising performing the following steps prior to step (d):

(g) accumulating a sum of the signals η

from each of N received pulses; and

(h) accumulating a sum of the signals 2γ

from each of said N received pulses whereby the signal ρ

depends on said N received pulses.

9. The method recited in claim 7 further comprising the steps of:

comparing the 4γ

² signal with a threshold value; and

providing as said ρ

signal the value γ

/α

when 4γ

² is less than said threshold value.