Communications: directive radio wave systems and devices (e.g. – Radar ew – Eccm
Reexamination Certificate
1988-06-27
2001-09-25
Hellner, Mark (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Radar ew
Eccm
C342S098000
Reexamination Certificate
active
06295017
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention pertains generally to semiactive missile guidance systems, and in particular to an improved system for detecting and tracking an airborne narrow band noise jammer, thereby enabling the deleterious effects of such jammer to be countered.
As is known, narrow band jamming is a self-screening electronic countermeasure (ECM) technique (for use particularly against continuous wave (CW) or Doppler radars) in which a narrow band noise jammer produces a jamming signal centered about the carrier frequency of a victim radar. The narrow band noise will not be detected by the jammer analysis circuits of the victim radar because such circuits test for the presence of jamming signals from noise jammers by searching a frequency band removed from the band in which the carrier frequency falls. Consequently, the signals will not be generated to command the victim radar to enter the so-called “home-on-jam”(HOJ) mode, nor will the victim radar declare a coherent target track.
Even if the jammer analysis circuitry in a semiactive missile were effective to command the victim radar to enter the HOJ mode, a narrow band jammer of the type here contemplated would nevertheless continue to prevent proper guidance. Thus, when the HOJ mode is entered in a semiactive guidance system, a speed gate (Doppler tracking loop) is swept across a predetermined acquisition bandwidth (in the order of 60 kHz), in an attempt to acquire a tracking signal on jammer energy. If, however, bandwidth of the narrow band jammer is low compared to the predetermined acquisition bandwidth, then the apparent duty cycle would not allow tracking on the jamming signal.
SUMMARY OF THE INVENTION
With the foregoing background of the invention in mind it is a primary object of this invention to provide narrow band jammer detection and tracking circuitry for a semi-active radar guidance system.
The foregoing and other objects of this invention are generally attained by providing logic circuitry in a victim radar that is adapted to produce a “lock” signal for a speed gate in such radar when signals indicative of a narrow band jammer occur on-two successive sweeps of the speed gate. Thus, during each of two successive sweeps, the logic circuitry is arranged: first, to produce (and to store) a signal indicative of the extant frequency of the speed gate when, as the result of the reception by the victim radar of a narrow band jamming signal, the speed gate enters a “pause” mode, the automatic gain control signal increases and there is no coherency between the received signal and a voltage-controlled oscillator (VCO) in the speed gate; and, then, if the signals indicative of the extant frequency of the speed gate are the same on the two successive sweeps, generates a “lock” signal whereby frequency and angle tracking of the narrow band jamming signal is commenced.
REFERENCES:
patent: 3569965 (1971-03-01), Bagley
patent: 3938148 (1976-02-01), Hobson
patent: 4011564 (1977-03-01), Gulick, Jr.
patent: 4190837 (1980-02-01), Salvavdon et al.
patent: 4241889 (1980-12-01), Schwellinger et al.
patent: 4256275 (1981-03-01), Flick et al.
patent: 4688042 (1987-08-01), Cronson et al.
“Radar Handbook,” pp 16-19 and 16-20, M. I. Skolnik, Editor-in-Chief, McGraw-Hill Book Co., 1970.
Dull Wesley T.
Girard Robert M.
Ivanov Alex
Marquis Joseph E.
Daly, Crowley & Mofford LLP
Hellner Mark
Raytheon Company
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