Communications – electrical: acoustic wave systems and devices – Echo systems – Distance or direction finding
Patent
1998-07-21
2000-02-01
Pihulic, Daniel T.
Communications, electrical: acoustic wave systems and devices
Echo systems
Distance or direction finding
G01S 728, G01S 752, H01Q 1502
Patent
active
060210966
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
Our present invention relates to beam forming in direction finding, detection, and survey systems and may be used in connection with acoustic and electromagnetic wave applications, including light waves. It is an object of the invention to achieve improved focussing of the beam and improved side lobe suppression in the directional pattern. In this way the resolution of such systems can be enhanced.
BACKGROUND OF THE INVENTION
With conventional direction finding systems the smallest possible beam width and hence the resolution not only depends on the wavelength and the wave propagation speed in the medium but primarily on the geometric dimensions of the receiving or transmitting array i.e. more the aperture. The shorter the wave length and the larger the antenna dimensions, the better the beam can be focussed. If the antenna consists of several individual transducers, it is not only possible to tilt the main direction of the antenna pattern by phase shifting the control signals or received signals, but also to influence the beam width and the side lobe suppression to a given amount by time delays.
From DE 42 09 352 C2 and from the book "Secondary Radar" by P. Honold, Siemens AG, 19971 p.45 to 48 it is known to achieve a better focussing of the antenne pattern by forming the difference between a summation pattern of two closely adjacent antennas and a corresponding differential pattern.
Furthermore, in the book "Introduction to Monopulse" by D. R. Rhodes, McGraw-Hill Book Company Inc., New York 1959, a method is described, where the summation signal is generated by summing up all transducer signals and subsequently deriving a magnitude or absolute value signal. By subsequently forming the difference between said summation signal and the differential signal the main lobe becomes narrower, but strong first side lobes appear at an angular distance of 10.degree. at both sides of the central main lobe.
SUMMARY OF THE INVENTION
With the invention the directivity of the beam is increased and the side lobes are more effectively suppressed by means of a new signal processing method and without any additional antenna restructuring. The common principle of all embodiments consists of dividing the aperture into two preferably identical transducers or groups of transducers and forming a relation between either the double magnitude of the direction finding signal of one of the two transducers or the sum of the magnitudes of the direction finding signals of both groups of transducers one the one side and a differential signal derived from the two direction finding signals one the other side. This relation can be a ratio of the signals or a difference between the signals. In the simplest case each group of transducers consists of one transducer each. The invention, however, can also be used with transducer rows, planar or curved transducer arrays, circular transducer arrays and the like.
Since the invention as a "summation signal" takes the double magnitude (absolute value) of the output signal of one of the two groups of transducers, or sums up the magnitudes of the output signals of the two groups of transducers, all side lobes, and in particular the otherwise specifically disturbing first side lobes, are located at the same position as the first side lobes of the differential signal, as derived from these magnitudes. Therefore, those side lobe signals cancel out each other when forming a signal quotient (ratio), and when forming a signal difference, respectively. This results in an essential reduction of the side lobes, when compared with the convential method of forming the summation signal.
BRIEF DESCRIPTION OF THE DRAWING
The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:
FIG. 1a is a diagrammatic illustration of a transducer array according to the invention;
FIG. 1b is a graph of the beam direction;
FIG. 2a-2d are various directional patterns illustrating the
REFERENCES:
patent: 5248984 (1993-09-01), Sezai
patent: 5268697 (1993-12-01), Sezai
patent: 5450089 (1995-09-01), Hui et al.
patent: 5485162 (1996-01-01), Sezai
patent: 5576711 (1996-11-01), Morris et al.
Eigenbrod Holger
Schlieter Heiko
Dubno Herbert
L-3 Communications Elac Nautik GmbH
Pihulic Daniel T.
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