Communications: directive radio wave systems and devices (e.g. – Return signal controls radar system – Receiver
Reexamination Certificate
1981-01-12
2001-03-13
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Return signal controls radar system
Receiver
C342S062000, C342S093000, C342S097000, C342S099000, C342S133000, C342S139000, C342S140000, C342S146000, C342S158000
Reexamination Certificate
active
06201496
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to single-channel search radars, in general, and more particularly, to apparatus for use therein which improves the estimation of the angle of a detected target within the search scan of the radar.
Most modern aircraft having weapon delivery systems generally employ a search radar for detecting targets of interest. In searching for a target, these radars usually scan through a spatial area with a plurality of looks or beam search samples. At each look, the radar may derive the amplitude of signals reflected from the target within the spatial area. Thereafter, the search radar may compute an estimated target scan angle from the amplitudes derived through the search scan. In turn, this estimated angle may be used to provide direction to the weapon delivery system for deployment of projectiles toward the target, for example.
An illustration of a typical scenario with regard to detecting a target is depicted in FIG.
1
. Suppose that the aircraft, denoted at
10
, is flying along a flight path
12
in the direction indicated by the solid arrow
14
. At a flight position P
1
, the search radar on-board the aircraft
10
may scan a spatial area
16
with its radar beam
18
in search of a target depicted in the figure as the dot
20
. In its search, the beam
18
of the radar may be scanned through a plurality of looks L
1
, L
2
, . . . , L
9
corresponding to a plurality of scan angles &thgr;
1
, &thgr;
2
, . . . , &thgr;
9
. At each look L
1
, the search radar may correspondingly derive an amplitude ai of the radar signal reflected from the target
20
. An idealistic example of a plot of amplitudes a
i
for the present example may appear as that shown by the x's on the dashed line in the graph of FIG.
2
.
Referring to
FIG. 2
, in some search radars, a simple centroiding procedure having the formula &Sgr;a
i
a
i
/&Sgr;a
i
, for example, has been used to compute the estimated target angle &thgr;
t
which, of course, falls between the scan angles &thgr;
5
and &thgr;
6
for the aircraft position P
1
in the present example. Accordingly, as the aircraft
10
moves to another position P
2
, another scan of looks may be performed and corresponding amplitudes computed by the search radar. Similarly, a curve of amplitudes for the search scan at position P
2
may be compiled as that shown by the second dashed line (P
2
) curve in FIG.
2
. It follows that the computed centroid of this second curve (P
2
) will be the estimated target angle with respect to the new aircraft position P
2
.
While for an ideal case, this simple centroiding procedure appears adequate for accurately estimating the true target angle for weapon delivery, it is evident that in more practical cases, the accuracy of the target angle estimation with this method may be somewhat degraded. For example, under most conditions, the aircraft search radar incurs undesirable noise at the input stages of the search radar itself. It happens that this instrumentation noise is inseparable from the echo signals returned from the target and thus tends to effect relatively large errors in the computation of the amplitude measurements of the target reflections through the various search beam directions. To further complicate matters, there is no guarantee that the beam scanning samples or looks will be scanned symmetrically about the true target angle. Moreover, even greater inaccuracies with the centroidal method can be expected when target scintillation provides further adverse noise sources.
Apparently, in view of the practical problems of noise as discussed above, the actual amplitude measurements derived by the search radar are not expected to follow any ideal curve fitting pattern for most practical sets of conditions. For example, the graph of
FIG. 3
illustrates a case in which actual amplitude measurements r(&thgr;
i
), denoted by X's, do not coincide with the ideal 1 amplitude measurements s(&thgr;
i
) denoted by the dots lying substantially on the dashed line curve. In this case, it is quite apparent that the simple centroid of the actual amplitude measurements will not result in an accurate estimation of the true target scan angle. Consequently, if the calculated simple centroid was used as the true target angle, it would cause an erroneous deployment angle for the weapon delivery system of the aircraft, for example.
From the above, it is evident that to be a viable piece of equipment for enhancing the effectiveness of weapon deployment, as one example, the search radar of the aircraft must accurately estimate the true scan angle of the target under even the most adverse conditions of noise with regard to both the aircraft and target flights and the internal operations of the radar itself. To accomplish this, it is felt that more sophisticated apparatus beyond that of a simple centroiding method is needed to process the actual amplitude measurements as derived by the search radar.
SUMMARY OF THE INVENTION
A search radar, which includes means operative to transmit and receive radar signals for a plurality of predetermined scan angles within a search scan; means operative to generate a plurality of signals representative of the predetermined scan angles; and means operative to generate a plurality of target amplitude measurement signals derived from the received radar signals respectively corresponding to the plurality of predetermined scan angles, is improved by the addition of apparatus for estimating the target angle within a search scan.
More specifically, the apparatus comprises a first means operative to compute an intermediate signal for each prespecified angle of the plurality in accordance with a first function based on the generated angle signal and the generated target amplitude measurement signal correspondingly associated therewith; second means operative to compute signals representative of moment relationships of the corresponding plurality of prespecified scan angle signals and intermediate signals for a search scan of the radar; and third means operative to compute a signal representative of the estimated target angle for a search scan in accordance with a second function based on the correspondingly associated moment-related signals of the search scan computed by the second means. In the search scan of the present embodiment, means are provided for detecting the presence of a target within the search scan of the radar from the drive amplitude measurement signals thereof and for generating a target detect signal as a result of the detected condition. In this embodiment, the improvement apparatus includes means operative in response to the generated target detect signal to compute the estimated target angles corresponding to the search scans.
In accordance with one aspect of the invention, the first means includes means for computing first signals representative of the logarithm of the derived target amplitude measurement signals; means for computing second signals proportionately representative of the square of the generated scan angle signals; and means for adding corresponding first and second signals to compute the intermediate signals associated therewith. Further, the second means includes means for accumulating separately the first signals, the second signals, the signals representative of the scan angles, and the intermediate signals over the period of a search scan. Still further, the third means includes means for generating first, second, third and fourth product signals representative of the products of: the third signal and moment signal of the second signals, the moment signal of the scan angle signals and the moment signal of the intermediate signals, the moment signal of the first signals and the third signal, and the moment signal of the scan angle signals with itself, respectively; means for generating fourth and fifth signals by subtracting the second product signal from the first product signal and by subtracting the fourth product signal from the third product signal, respectively; and means for generating the signal re
Northrop Grumman Corporation
Sotomayor John B.
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