Communications: directive radio wave systems and devices (e.g. – Return signal controls external device – Radar mounted on and controls land vehicle
Reexamination Certificate
2001-01-02
2003-06-03
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Return signal controls external device
Radar mounted on and controls land vehicle
C342S128000, C342S133000, C342S147000, C342S173000
Reexamination Certificate
active
06573859
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radar apparatus provided with a reception array antenna consisting of a plurality of antenna elements and constructed to detect a bearing of a target by signal processing on individual element signals received through the respective antenna elements.
2. Related Background Art
A bearing of a target can be determined by a scan with an antenna beam narrowed down to a desired width.
Scanning methods can generally be classified into mechanical scanning methods and electronic scanning methods and a digital beamforming (DBF) scanning method can be listed as one of the electronic scanning methods.
The DBF scanning method is a method of carrying out the scan with the antenna beam by making use of the DBF technology in which the antenna beam can be formed in any desired direction by using the array antenna with a plurality of antenna elements as a receiving antenna, performing a phase shift process by digital signal processing on the individual element signals received through the respective antenna elements, and carrying out a synthesis process.
The DBF scanning method eliminates the need for rotation of the antenna, which was required in the mechanical scanning methods. Accordingly, it obviates the need for a driving mechanism for rotating the antenna and thus has the advantages of being resistant to vibration and permitting reduction in size and weight. While making the most of such advantages, research has been conducted heretofore on application to on-vehicle radar apparatus.
Incidentally, for enhancing the bearing resolution in the DBF scanning method, it is necessary to increase the size of the antenna and increase is inevitable in the digital operation load for formation of beam. For that reason, the bearing resolution has a limit under the constraints that the radar apparatus has to be installed in a limited space or that the detection result has to be given within an effective time.
Particularly, the bearing resolution degrades with distance to the target. For example, supposing two preceding cars running with a predetermined spacing between them are targets to be detected, it will become more difficult to separate and detect the two cars as the distance increases.
There were thus needs for the radar apparatus capable of enhancing the bearing resolution as occasion demands.
SUMMARY OF THE INVENTION
A radar apparatus according to the present invention has been accomplished in order to meet such needs and comprises a reception array antenna having a plurality of antenna elements, first bearing detecting means for detecting a bearing of a target by carrying out signal processing on individual element signals received on element-by-element basis through the respective antenna elements, and second bearing detecting means for detecting a bearing of a target by carrying out signal processing different from that of the first bearing detecting means, on the individual element signals received through the respective antenna elements.
Since the apparatus comprises two bearing detecting means of the first bearing detecting means and second bearing detecting means as target bearing acquiring means, both results of the detection by the two means, or either one of results of the detection can be selectively utilized as occasion demands.
It is desirable that the first bearing detecting means impose a lighter operational load for detection of the target bearing than the second bearing detecting means and that the second bearing detecting means posses a higher target bearing resolution than the first bearing detecting means. The first bearing detecting means is applied to detection of a target existing in a relatively near range and the second bearing detecting means to detection of a target existing in a relatively far range.
This radar apparatus is desirably an FM-CW radar apparatus which uses a transmitted signal of frequency-modulated continuous wave and which acquires the distance to the target from a beat frequency between a received signal through the reception array antenna and the transmitted signal.
Further, it is desirable that the apparatus further comprise a reception circuit for acquiring beat signals by mixing the transmitted signal with the received signals through the antenna elements and converting the beat signal gained every antenna element to a digital beat signal, that the first bearing detecting means be means for performing a digital beamforming process on a plurality of element-by-element digital beat signals to form an antenna beam in a plurality of directions and detecting the bearing of the target, and that the second bearing detecting means be means for carrying out an analysis by digital signal processing on a phase difference between the plurality of element-by-element digital beat signals to detect the bearing of the target as point information.
The first bearing detecting means has the advantages of being capable of detecting not only the center position of the target but also the width thereof and necessitating the processing time shorter than the second bearing detecting means, and the second bearing detecting means has the advantage of the bearing resolution higher than the first bearing detecting means. The target can be detected with accuracy by properly selecting a bearing detecting means to be used in consideration of these advantages.
One of criteria for selection of the first and second bearing detecting means can be the magnitude of the beat frequency. For example, the target bearing can be detected using the first bearing detecting means for the beat signal of the beat frequency not more than a predetermined value, and the target bearing can be detected using the second bearing detecting means for the beat signal of the beat frequency larger than the predetermined value.
The beat frequency is proportional to “distance±relative speed.” Namely, it is roughly proportional to the distance though there occurs some error depending upon the difference in relative speed. When the target is present in the near range, the beat frequency takes a smaller value than when it is present in the far range.
On the other hand, the bearing resolution of the first bearing detecting means degrades with distance to the target. As the distance to the target increases, it is often the case that it becomes unnecessary to dare to acquire the information about the width of the target.
Thus, the first bearing detecting means is used for the beat signal of the beat frequency not more than the predetermined value, while the second bearing detecting means for the beat signal of the beat frequency larger than the predetermined value, whereby it becomes feasible to acquire the width information for the target in the near range as well while maintaining the necessary bearing resolution throughout the entire range of distances to be detected.
This radar apparatus is desirably provided with beat frequency detecting means for detecting a beat frequency indicating an approximate distance at which a target is assumed to exist, prior to the detection of the bearing of the target by the first bearing detecting means or by the second bearing detecting means.
When the target bearing detection by the first bearing detecting means or by the second bearing detecting means is carried out with limiting the detection to the beat frequency gained by the beat frequency detecting means, the processing time can be reduced greatly, as compared with the case wherein the target bearing detection is carried out throughout the entire beat frequency range.
The first bearing detecting means can detect the bearing of the target from a position of a peak in a power distribution with a variable of bearing and detect the target width from a peak width, i.e., from a width of the distribution at a position where power is lowered by a predetermined amount from the peak position.
If the target width is not less than a predetermined value, there is the possibility of fusion of targets. In that case, the bearing of the target
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Gregory Bernarr E.
Toyota Jidosha & Kabushiki Kaisha
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