US3797016A
Expired / Lapsed
US
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Digital moving target indicator radar system incorporating modulo-n components
Assignee: Westinghouse Electric Corp
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Filing: 1972-08-04
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Granted: 1974-03-12
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Expires: 1992-08-04
Abstract
Abstract A radar system is disclosed utilizing digital techniques for implementing a moving target indicator (MTI) or pulse doppler type of radar system. More specifically, the radar system includes an MTI filter or canceler circuit for suppressing clutter signals corresponding to stationary and/or relatively slow-moving targets, while providing an output signal indicative of echo signals received from relatively fast-moving targets. The canceling circuit of this invention achieves moving target detection with digital apparatus having a capability of processing only a limited number of digital bits. The MTI filter of this invention incorporates modulo-N components having a modulus or linear range so that the minimum detectable signal of interest lies therein. The higher magnitudes of signals corresponding to echo signals received from stationary and/or slowly-moving objects will be canceled by the canceling circuit, normally. If echo signals are developed from moving targets that are of higher magnitudes than the modulus, these signals will be ''''aliased'''' by the modulo-N components about the levels N/2 and N/2 to provide a noise-like output. Regardless of the amplitude of the echo signals derived from a relatively fast-moving target, detecting means is provided to detect the absence or presence of such signals.
Inventors
- 👤 R Martin
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 16:59
CPC Classifications
G; G01; G01S; G01S13/00; G01S13/02; G01S13/50; G01S13/52; G01S13/522; G01S13/524; G01S13/526
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
185 words
In a moving target indicator radar system, a canceling circuit for suppressing echo signals from relatively slow-moving and/or stationary targets, said canceling circuit comprising: a. modulo-N reducer means for converting signals in accordance with a modulo-arithmetic transfer characteristic to provide an output signal whose amplitude is within the modulus N range; b. delay means for imparting a predetermined delay to the converted signals; c. modulo-N multiplier means for multiplying the delayed signals in accordance with selected coefficients and converting the multiplied signals in accordance with the modulo-arithmetic transfer characteristic to provide output signals indicative of the multiplied delayed signals whose amplitudes are within the modulus N range; and d. modulo-N summing means for summing the delayed multiplied signals and for converting the summed signals in accordance with the modulo-arithmetic transfer characteristic to provide a summed output signal whose amplitude is within the modulus N range, the coefficients of said modulo-N multiplier means being selected to suppress those signals of relatively slowly changing amplitude corresponding to relatively slow-moving and/or stationary targets and to provide an output signal corresponding to those signals derived from relatively fastmoving targets.
Claim 2
Dependent Claim
185 words
In a moving target indicator radar system, a canceling circuit for suppressing echo signals from relatively slow-moving and/or stationary targets, said canceling circuit comprising: a. modulo-N reducer means for converting signals in accordance with a modulo-arithmetic transfer characteristic to provide an output signal whose amplitude is within the modulus N range; b. delay means for imparting a predetermined delay to the converted signals; c. modulo-N multiplier means for multiplying the delayed signals in accordance with selected coefficients and converting the multiplied signals in accordance with the modulo-arithmetic transfer characteristic to provide output signals indicative of the multiplied delayed signals whose amplitudes are within the modulus N range; and d. modulo-N summing means for summing the delayed multiplied signals and for converting the summed signals in accordance with the modulo-arithmetic transfer characteristic to provide a summed output signal whose amplitude is within the modulus N range, the coefficients of said modulo-N multiplier means being selected to suppress those signals of relatively slowly changing amplitude corresponding to relatively slow-moving and/or stationary targets and to provide an output signal corresponding to those signals derived from relatively fastmoving targets.
Claim 3
Dependent Claim
93 words
A canceling circuit as claimed in claim 1, wherein the summed signals is applied to detector means for detecting the presence of an echo signal corresponding to a relatively fast-moving object, to provide a signal indicative thereof, integration means for integrating the signal derived from said detector means, and threshold detector means for determining whether the amplitude of the integrated signal derived from said integrator means is above or below a predetermined level, the threshold level of said threshold detector means being set to indicate the presence of a relatively fast-moving target signal.
Claim 4
Dependent Claim
79 words
A canceling circuit as claimed in claim 1, wherein the modulo-arithmetic transfer characteristic controls the converted output signal of said modulo-N reducer means such that if the input signal thereto is less than -N/2, then the output signal equals kN, where k is the smallest integer such that kN >-N/2 and, if the input signal is equal to or greater than N/2, then the output signal equals -jN, where j is the smallest integer such that -jN < N/2.
Claim 5
Dependent Claim
107 words
A canceling circuit as claimed in claim 3, wherein the multiplied output signal of said modulo-N multiplier is controlled in accordance with the modulo-arithmetic transfer characteristic such that if the product P of the echo signal and a selected coefficient is less than -N/2, then the product output signal PN of the modulo-N multiplier means if P + kN, where k is the smallest integer such that (P + kN) < -N/2, and if the product signal P > or = N/2, then the product output signal PN of said modulo-N multiplier means equals (P -jN), where j is the smallest integer such that (P -jN)< N/2.
Claim 6
Dependent Claim
103 words
A canceling circuit as claimed in claim 3, wherein the transfer characteristic of said modulo-N summing means is chosen such that the summed input signals of said modulo-N summing means Sigma is less than -N/2, then the output signal of said modulo-N summing means Sigma N is ( Sigma +kN), where k is the smallest integer such that ( Sigma +kN) <-N/2, and if the summed input signals of said modulo-N summing means Sigma > or = N/2, then the output signal of said modulo-N summing Sigma N ( Sigma -jN) where j is the smallest integer such that ( Sigma -jN) <N/2.
Claim 7
Dependent Claim
51 words
A canceling circuit as claimed in claim 2, wherein the predetermined level of said threshold detector means is set to distinguish against thermal noise inherent in the radar system and to permit an echo signal corresponding to a relatively fast-moving target to provide an output signal from said threshold detector means.
Claim 8
Dependent Claim
42 words
A canceling circuit as claimed in claim 6, wherein the predetermined level of said threshold detector means is set such that the probability of occurrence of thermal noise of an amplitude in excess of the predetermined level, is below a predetermined number.
Claim 9
Dependent Claim
63 words
A canceling circuit as claimed in claim 1, wherein the modulus N of said modulo-N reducer means, said modulo-N multiplier means, and said modulo-N summing means is selected such that the peak-to-peak value of a signal, corresponding to a minimum detectable moving-target echo signal, together with the effects of receiver thermal noise, lie substantially within the linear modulus range - N/2 to N/2.
Claim 10
Dependent Claim
22 words
A canceling circuit as claimed in claim 8, wherein the modulus N is chosen to be equal to or greater than 32.
Claim 11
Dependent Claim
31 words
A canceling circuit as claimed in claim 1, wherein each of said modulo-N reducer means, delay means, modulo-N multiplier means, and modulo-N summing means is of a five-bit data handling capability.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-03-11 | 1977-09-10 | 1978-03-12 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-03-11 | 1981-09-10 | 1982-03-12 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-03-11 | 1985-09-10 | 1986-03-12 | $7700.00 | Window Closed / Lapsed |