Communications: directive radio wave systems and devices (e.g. – Clutter elimination
Patent
1987-04-16
1988-05-03
Blum, Theodore M.
Communications: directive radio wave systems and devices (e.g.,
Clutter elimination
342195, 364724, G01S 1386
Patent
active
047423536
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a radar signal digital processor which can suppress clutter disturbances and enhance useful signals of given Doppler frequency. It can approximate the principle of operation of the optimum processor, which is the processor which maximizes the signal-to-noise ratio. It is furthermore capable of suppressing, in an adaptive way, clutter having an approximatively Gaussian power spectrum. Its performance is better than that of an adaptive moving target indicator MTI (MTIA) followed by a coherent integrator.
The invention presented herein relates to the field of radars, and more exactly that of radar signal processing for disturbance suppression. The device may be inserted within an integrated radar signal digital processor, between the analogue-to-digital converter and the modulus extractor. The specific tasks of the device (disturbance suppression and useful signal enhancement), are obtained in an adaptive manner as far as disturbance and useful signal to be detected (parameter variations) are concerned.
This adaptiveness provides a way to overcome the limitations related to fixed disturbance filtering, while optimizing, at the same time, system capability to detect useful targets. Signal processors, which are presently implemented by means of digital circuitry, receive at their input the radar video signal which is detected coherently and coverted into digital format. They provide as an output an indication of targets which may be present (detection process) by attenuating undesirable signals. The elimination of undesirable signals arising out of reflections caused by natural or artificial obstacles (clutter), is obtained in current radar technique by means of MTI filtering (Moving Target Indicator) described in many articles and books, among them: Graw Hill, New York; 1980;
In current practice, it is customary to resort to a more flexible type of filtering than the one above, which is that of 1.sup.st and 2.sup.nd generation MTD, described in Chapter 4.7 of Skolnik's book and in many other works, among them: AGARD Conf. Proceedings No. 195, June 14-17, 1976, pp. 14-1 to 14-10; Surveillance Radar Systems"--IEE Trans., Vol. AES 15, No. July 1979, pp. 508-516; 95, June 1, 1981; Environment". IEEE Int. Radar Conf., 1980, pp. 219-224;
The technological improvements achieved of recent years have given way to the development of devices having an improved adaptivity. An example of this is the A-MTD processor, such as that described in: Processor for Search Radars having a set of Doppler filters and a threshold system selectable upon type of disturbance, Italian patent No. 48701/A/83, where the task is that of selecting one of three filter shapes, each of which is designed for a given level of the disturbance to be suppressed, as a function of the measured clutter level.
A further example in this area can be found in the adaptive MTI device: IEEE Trans. on AES Vol. 14 No. 6 Nov. 1978.
This latter device implements the function of a normal MTI filter over clutter disturbance caused by moving obstacles by means of an estimate of the disturbance Doppler phase.
The limits, in performance terms, of the processors mentioned above are as follows:
1. The fixed type of filtering, because pre-designed to cater to a specific disturbance situation, degrades performance obtainable in an environment which has different disturbance characteristics.
2. The degree of freedom, typically the number of processed pulses, are not exploited effectively in the partitioning of pulses between disturbance suppression and useful signal integration.
3. The adaptive type of filtering, mentioned above, gives way to only a partial adaptation to the unknown characteristics of the disturbance. In one case we adapt to its power level, in another we adapt to its average Doppler frequency. In both cases there is no adaptation to the shape of the disturbance power spectrum.
SUMMARY OF THE INVENTION
The limitations discussed above are overcome by the present invention, as explained in the fo
REFERENCES:
patent: 3872290 (1975-03-01), Crooke et al.
patent: 4217584 (1980-08-01), Lombardi et al.
patent: 4377793 (1983-03-01), Horna
patent: 4578676 (1986-03-01), Harrison, Jr.
patent: 4584659 (1986-04-01), Stikvoort
V. Buhring et al., "Ein Adaptives Filter zur Unterdruckung von Radarstorungen mit Unbekanntem Spektrum"; Frequenz, (vol. 30, #9, 1976; pp. 238-243).
V. Hansen et al., "A Comparison of the Performance Against Clutter of Optimum, Pulsed Doppler and MTI Processors"; IEEE Internt'l Radar Conf. Record (1980), pp. 211-218.
D'Addio Egidio
Farina Alfonso
Blum Theodore M.
Gregory Bernarr
Selenia - Industrie Elettroniche Associate - S.p.A.
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