Communications: directive radio wave systems and devices (e.g. – Radar ew – Eccm
Reexamination Certificate
1977-10-21
2001-07-31
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Radar ew
Eccm
C342S159000, C342S194000, C342S195000, C342S379000
Reexamination Certificate
active
06268821
ABSTRACT:
BACKGROUND OF THE INVENTION
In military applications involving a radar system such as a missile tracking radar which tracks a friendly signal from a missile, an enemy jamming signal may be present outside the main lobe of the radiation pattern of the radar antenna to be received via a sidelobe of the radiation pattern which has a very much lower gain than the gain of the main lobe. An auxiliary antenna having an omnidirectional radiation pattern may be utilized to produce a second received jamming signal which can be subtracted from that received by the sidelobe of the aforementioned tracking antenna, or main antenna, to remove the effect of the jamming signal as a source of error in the tracking operation. A problem arises in that the electrical phase centers of the two antennas must necessarily be displaced with the result that, for the typical broad band jamming signal, a temporal delay exits between the propagations from the jamming source to each of the antennas, this producing a decorrelation between the waveforms and a difference in the phases of the received jamming signals. The phase differences are frequency dependent with the result that when the jamming signal from the auxiliary antenna is combined with the jamming signal received by the sidelobe of the main antenna, good cancellation of the jamming signal is obtained only over a relatively narrow spectrum of the passband of the radar system, other frequency components of the jamming signal lying within the passband of the radar system being attenuated, or cancelled, to a lesser extent. Thereby, an undesireably large amount of jamming signal power is found with the friendly signal from the missile resulting in a diminution of precision in tracking the friendly signal.
SUMMARY OF THE INVENTION
The aforementioned problem is overcome and other advantages are provided by a sidelobe canceller system for a radar employing a main radar antenna and an auxiliary radar antenna wherein, in accordance with the invention, two identical sets of bandpass filters are utilized for receiving the signal of the auxiliary antenna and the signal of the main antenna. The main antenna may have the aforementioned radiation pattern of a main lobe and relatively small sidelobes, while the auxiliary antenna has the aforementioned omnidirectional radiation pattern. The jamming component of signal appearing in each bandpass filter of the main antenna is separately cancelled by use of the auxiliary antenna signal appearing in the corresponding bandpass filter of the auxiliary antenna. Thereafter, each of the signals, including a residue of the jammer cancellation, appearing in the respective ones of the bandpass filters of the main antenna are summed together to regenerate the complete received signal of the main antenna, the received signal comprising the aforementioned friendly signal with a residual amount of uncancelled jamming signal.
The widths of the bandpass filters are sufficiently small such that the temporal delays between the propagation times of the jamming signals to each of the radar antennas is small compared to the response time of an individual one of the bandpass filters. Thereby, the amount of decorrelation between the waveforms of the portions of the jamming signal appearing within a bandpass filter of the main antenna and the corresponding filter of the auxiliary antenna are sufficiently small such that adequate cancelling can be accomplished with respect to that portion of the jamming signal.
Upon the aforementioned summing together of the signals with the residues in each of the bandpass filters of the main antenna, it is found that the resulting uncancelled residue is very much smaller than that of the friendly signal appearing in the summation of the signals; thus, the jamming signal has been adequately cancelled.
With respect to the cancellation of the portion of the jamming signal appearing in an individual one of the bandpass filters of the main antenna, a replica jamming signal, obtained with the aid of a reference signal from the corresponding bandpass filter of the auxiliary antenna, is subtracted from the aforementioned signal appearing in the individual one of the bandpass filters of the main antenna. The subtraction produces a cancelled signal, the adequacy of the cancelling of the cancelled signal depending on the amplitude and phase of the replica signal. The cancelled signal is detected by inphase and quadrature synchronous detectors utilizing the reference signal of the auxiliary antenna, the synchronous detection producing orthogonal vector representations of the cancelled signal relative to the reference signal which facilitate a vector rotation of the reference signal to bring it into phase with the aforementioned signal of the corresponding bandpass filter of the main antenna. The synchronously detected signals are filtered and then applied as multiplying factors to a pair of multipliers for a complex multiplication times the reference signal. The multiplication may be accomplished by amplitude modulators and alters the amplitude of the vector components to produce the vector rotation and magnitude scaling of the reference signal. The products of the pair of multipliers are summed together to produce the replica signal. The foregoing replica generation circuitry operates in the form of a feedback loop wherein the loop gain minimizes differences between the amplitude and phase of the replica and that of the signal appearing in the main antenna.
REFERENCES:
patent: 3202990 (1965-08-01), Howells
patent: 3611375 (1971-10-01), Chambers et al.
patent: 3860924 (1975-01-01), Evans
patent: 3879661 (1975-04-01), Collins
patent: 3881177 (1975-04-01), Len et al.
patent: 3938153 (1976-02-01), Lewis et al.
patent: 3943511 (1976-03-01), Evans et al.
patent: 3978483 (1976-08-01), Lewis et al.
patent: 4042925 (1977-08-01), Albanese et al.
patent: 4057802 (1977-11-01), Dollinger
Hansen Vilhelm Gregers
Shrader William W.
Daly, Crowley & Mofford LLP
Raytheon Company
Sotomayor John B.
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