Complementary-sequence pulse radar with matched filtering following doppler filtering

• US 5,151,702 A
• Filed: 07/22/1991
• Issued: 09/29/1992
• Est. Priority Date: 07/22/1991
• Status: Expired due to Fees

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: General Electric Company
• Inventors: Urkowitz, Harry
• Primary Examiner(s): Barron, Jr., Gilberto
• Application Number:
  US07/734,003
• Time in Patent Office: 435 Days
• Field of Search: 342/109, 342/111, 342/116, 342/132, 342/134, 342/145, 342/189, 342/196, 342/201
• US Class Current: 342/134
• CPC Class Codes: G01S 13/284 using coded pulses
• CPC Class Codes: G01S 13/522 using transmissions of interrupted pulse modulated waves

Abstract

A radar generates first and second mutually complementary binary code sequences. The autocorrelation functions of the first and second pulse sequences are selected so that, in the sum of their autocorrelation functions, the main lobes add, and the sidelobes are of equal amplitude and opposite polarity, and therefore cancel. The radar sequentially transmits dispersed pulses in which the chips are phase modulated with the two codes. The received pulses are applied uncompressed to the input of a Doppler filter bank, which filters them into various Doppler channels, each representative of a particular radial velocity of the target. Within each channel, the received signals modulated by the first code are matched-filtered by a filter matched to the first code, to produce a first time-compressed pulse, and those modulated by the second code are matched-filtered by a filter matched to the second code, to produce a second time compressed pulse. The time-compressed pulses include a main lobe which represents the range of the target, and also include sidelobes which may introduce range ambiguity. The first and second time compressed pulses are added together in each Doppler channel, to produce, in each channel, range pulses in which the range sidelobes are suppressed. Thus, range sidelobe suppression is accomplished without the use of discrete range sidelobe suppressors.

Claims

1. A method for detecting anomalies, comprising the steps of:

transmitting toward an anomaly a first pulse set consisting of a predetermined plurality of first pulses, said pulses of said first set being dispersed in time pursuant to a predetermined phase code;

transmitting toward said anomaly a second pulse set consisting of said predetermined plurality of second pulses, said pulses of said second set being dispersed in time pursuant to a second phase code selected to be complementary to said predetermined phase code in a manner such that, after pulse compression of said first and second pulses, the resulting range sidelobes are substantially equal in amplitude and opposite in sign;

receiving echoes of said first and second pulses reflected from said anomaly to produce received first and second pulse sets;

Doppler filtering said received first and second pulse sets into a plurality of frequency components to produce a sequence of range values for each frequency component, each of said sequence of range values including said first and second code sequences;

for each said frequency components, matched filtering each of said first and second code sequences of range values to produce first and second compressed pulses;

summing said first and second compressed pulses; and

after said Doppler filtering step, converting at least some of said plurality of frequency components to a common frequency.

2. A method according to claim 1, wherein said transmitting steps each include the step of transmitting an electromagnetic pulse set.

3. A method according to claim 1, wherein said transmitting steps are time-sequential.

4. A method according to claim 1 wherein said step of matched filtering includes the steps of:

matched filtering said first pulses; and

matched filtering said second pulses following said step of matched filtering said first pulses.

5. A method according to claim 1, wherein said step of converting at least some of said plurality of frequency components to a common frequency includes the step of converting at least some of said plurality of frequency components to a common baseband frequency.

6. A method according to claim 1, wherein said transmitting steps are performed in time sequence, and said summing step includes the further step of delaying the earlier of said first and second compressed pulses.

7. A method according to claim 6, wherein said delaying step comprises the step of delaying by the duration of one of said first and second code sequences.

8. An apparatus for detecting targets, comprising:

code generating means for generating first and second complementary code sequences, said first and second complementary codes being selected so their autocorrelations have main lobes of the same polarity, and sidelobes of the same amplitude and mutually opposite polarity;

transmitting means coupled to said code generating means for transmitting electromagnetic pulses modulated by said first and second complementary codes;

receiving means for receiving echoes of said pulses reflected from a target, for producing a sequence of range values of received first and second pulse sets, said received first pulse set being modulated by said first code sequence, and said received second pulse set being modulated by said second code sequence;

Doppler filtering means including a plurality of Doppler channels, said Doppler filtering means being coupled to said receiving means, for filtering said received first and second pulse sets into a plurality of frequency components, each associated with one of said Doppler channels, for producing in at least one of said Doppler channels, if the radial velocity of said target is appropriate, a sequence of range values including said first and second code sequences;

matched filtering means coupled to each of said Doppler channels, for selectively matched filtering said first and second code sequences to thereby produce first and second compressed pulses, respectively;

summing means coupled to said matched filtering means for summing together said first and second compressed pulses, whereby the main lobes of said compressed pulses add, and the sidelobes tend to cancel;

wherein said matched filtering means comprises single pole, double throw switch means coupled to each of said Doppler channels for selectively switching said sequence of range values including said first code sequence to a first path, and for selectively switching said sequence of range values including said second code sequence to a second path;

first code matched filter means matched to said first code sequence coupled to said first path; and

second code matched filter means matched to said second code sequence coupled to said second path.

9. An apparatus according to claim 8, wherein said switch means further comprises:

switch control means for controlling said switch means by switching said switching means at a time near the first pulse transmitted in response to of said first and second complementary code sequences.

10. An apparatus according to claim 8, wherein said code generating means comprises means for generating first and second complementary binary codes.

11. An apparatus according to claim 10 wherein said transmitting means comprises means for transmitting electromagnetic pulses phase-modulated by said first and second complementary codes.