Communications: directive radio wave systems and devices (e.g. – Clutter elimination
Patent
1986-05-27
1987-12-08
Tubbesing, T. H.
Communications: directive radio wave systems and devices (e.g.,
Clutter elimination
342194, 342195, G01S 766
Patent
active
047121092
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a device for the identification of undesirable echoes in radar systems.
Such invention belongs to the radar field and more exactly to the field of surveillance or tracking radars.
At present, undesirable echoes are recognized by relying upon two distinct techniques: overage of the power level over a group of echoes relevant to the same impulse transmitted and further comparison with a fixed precalculated threshold; by the receiver input power into a group of echoes relevant to the same impulse transmitted.
Such techniques, however, suffer poor sensitivity, and present poor discrimination between echo sources (clutter, jammer, asynchronous pulses and targets).
SUMMARY OF THE INVENTION
An object of the present invention is a device which can detect the presence of undesirable echoes having large azimuth correlation coefficient (clutter) and discriminate them against echoes having small correlation coefficient (jammer, asynchronous pulse). The device operates on an estimate of the auto correlation function C (which here coincides with the autocovariance function as the mean value is nil, as shown by Papoulis: Probability, Random Variables and Stochastic Processes, International Student Edition McGraw Hill paragraph 9-3) by averaging, over N range bins, the complex product of the signal received Z.sub.K (t.sub.1) related to the K-th range bin and to generic instant t.sub.1 and the complex conjugate value Z.sub.K *(t.sub.1 +T) still relevant to the K-th range bin, but at time t.sub.1 +T (where T is the pulse repetition period): ##EQU1##
The crossing of a threshold S by the modulus /C(T)/ of the estimated value, indicates the presence of a correlated disturbance in azimuth (clutter) in the examined range bins (i.e. range cells).
The threshold S is suitably calculated to obtain the desired false detection probability.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described with reference to some of its actually preferred forms of implementation and these are reported as an illustration, are not limited to these and make reference to the drawings attached where:
FIG. 1 shows a block diagram of the device; and:
FIG. 2 shows a block diagram of a variant of the present invention which is insensitive to interference, particularly pulsed interference.
DETAILED DESCRIPTION OF THE INVENTION
The figures may be described in further detail as follows:
FIG. 1 shows a block diagram of the device, where the elements listed below have the indicated reference numerals: cell of the radar), 4;
FIG. 2 shows a block diagram of a variant of the present invention, where blocks 1,2,3,4,8 have already been described in FIG. 1.
The further blocks are meant to make the device insensitive to interference, particularly to pulsed interference.
They are:
Blocks A and B within dashed lines are two alternative ways of selecting the smaller of two inputs and further comparing it with the prefixed threshold.
Block A shows the selector of smaller input 12 and the comparator with prefixed threshold 8 (as already seen in FIG. 1).
Block B shows two comparators 14 and an AND logic gate 15.
The present invention will now be described with reference to the two preferred implementations. (Note that I and Q are the two components, in phase and in quadrature, of the input signal Z(t), represented in complex form:
In FIG. 1, the two components I and Q of input signal Z(t) to be analyzed are sampled at instants t.sub.0, t.sub.0 + . . . t.sub.0 +n, where t.sub.0 is the initial time instant and n is the sampling period. These samples are delayed by time T and are suitably processed to obtain their complex conjugate. Thereafter the complex product is carried out to obtain autocorrelation function C.sub.K+j (T) to be averaged over N samples. This value is sent to a delay line with N taps (having elementary delays) the outputs of which are added, divided by N and sent to a modulus extractor to obtain /C(T)/. The value obtained is compared to threshold S, settable, which d
REFERENCES:
patent: 4044352 (1977-08-01), Wilmot
patent: 4086592 (1978-04-01), Lewis et al.
patent: 4217584 (1980-08-01), Lombardi et al.
patent: 4578676 (1986-03-01), Harrison, Jr.
Nitzberg, "Low-Loss Almost Constant False Alarm Rate Processors"; IEEE Trans. on Aerospace and Electronic Systems (vol. AES-15, #5, 9/79; New York).
Traynar et al, "C.C.D. Integration Techniques for Clutter Reduction in Radar Systems"; The Radio and Electronic Engineer (vol. 50; No. 5; 5/80; London).
Galati Gaspare
Orsini Mario
Gregory Bernarr Earl
Selenia - Industrie Elettroniche Associate - S.p.A.
Tubbesing T. H.
LandOfFree
Device for the identification of undesirable echoes in radar sys does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Device for the identification of undesirable echoes in radar sys, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Device for the identification of undesirable echoes in radar sys will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-24128