Communications: directive radio wave systems and devices (e.g. – With particular circuit – Display
Reexamination Certificate
1999-06-09
2001-03-06
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
With particular circuit
Display
C342S185000, C342S179000
Reexamination Certificate
active
06198429
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to radar apparatuses, and like systems, in which a received echo signal originally formatted for a polar coordinate system is converted into an image signal for a Cartesian coordinate system and the image signal is stored in an image memory and then presented on a raster-scan display. The invention also relates to a method of writing the image signal in the image memory. Particularly, the invention relates to radar apparatuses and method which are capable of improving quality of displayed images.
One way to improve image quality is to use scan-to-scan correlation on received echo data.
In a system designed to convert received echo signals formatted for a polar coordinate system into signals for a Cartesian coordinate system and present the converted signals in raster-scan format, sampling points of an echo signal are densely distributed near the center of scanning, or sweep origin, and gradually become more sparse outward from the sweep origin as illustrated in FIG.
13
. Accordingly, when the signal is converted into data for Cartesian coordinates (x, y), increasingly larger numbers of values of received data are allocated to pixels closer to the sweep origin, which corresponds to a central address in an image memory. If values of the received data for a particular pixel are simply written in succession over previously stored data in an memory element having a corresponding address in the image memory when more than one sampling point is allocated to that pixel, only the last written value will be finally preserved as effective data in the memory element for the pixel. This causes such a problem that when data having a high signal level is received halfway in the process of writing successive values for a single pixel, no information on the high-level signal is preserved in the image memory.
A known example of previous approaches directed to the solution of this problem is a maximum data sampling method, in which data having a maximum value among all received data for each pixel is written in a memory. In the maximum data sampling method, as disclosed in Japanese Examined Patent Publication Nos. 3-582 and 3-11669, for example, there is provided a first sample detecting circuit which detects a first access to an address corresponding to a specified pixel in the process of writing received data in an image memory. When the first sample detecting circuit has just detected the first sample allocated to a given pixel, the received data is written in the corresponding memory element. If newly received data is a second or later sample (and not the first sample) allocated to the pixel, a comparison is made between the previously written data and the newly received data, and the data whichever having a larger value is written in the same address, overwriting the existing data. This overwriting operation is repetitively carried out and, as a consequence, all the received data for each pixel are compared and the data having the maximum value is extracted and stored in the relevant memory element in the image memory.
Apart from the maximum data sampling method, radar systems usually employ a scan-to-scan correlation technique, in which echo signals derived from one antenna rotation after another are compared with each other, pixel to pixel, to eliminate unwanted signals, such as sea clutter. More specifically, a set of data obtained from the latest antenna rotation is compared with a set of data previously stored in a memory based on preceding antenna rotations, and data to be newly written in the memory is determined from this comparison. In one form of the correlation technique, the existing data derived from the preceding antenna rotations and the new data are simply averaged and mean values of the data thus obtained are written in the memory, overwriting the existing data. An example of the scan-to-scan correlation technique is disclosed in Japanese Examined Patent Publication No. 3-12266.
In a system employing the scan-to-scan correlation technique as described in the aforementioned Patent Publications, however, it is impossible to jointly employ the maximum data sampling method. Maximum data sampling and scan-to-scan correlation operations are performed by circuits having similar configurations because these operations have some similarity in that successively received data are compared and processed for each individual pixel. It is, however, impossible to simultaneously perform both of these operations by a single circuit. Even when two independent processing circuits are connected in series to carry out the two operations together, it is impossible to perform the scan-to-scan correlation operation using the data obtained by the maximum data sampling operation which is based simply on the detection of the first sample for each pixel, for reasons (1) and (2) explained below.
(1) Both the maximum data sampling operation and the scan-to-scan correlation operation determine values of data to be stored in a memory during each antenna rotation based on a comparison between existing data and newly received data as discussed above. However, the two operations differ in that the maximum data sampling operation, as applied to a radar system, for example, involves repetitive processing cycles which are conducted for each pixel every antenna rotation, whereas the scan-to-scan correlation operation involves only one processing cycle conducted for each pixel in one antenna rotation. It is therefore impossible to perform the two operations at the same time by a single circuit.
(2) In a case where maximum data sampling and scan-to-scan correlation circuits are separately provided and connected in series to successively perform the two operations, there arises another problem which is described below.
Since only one processing cycle is conducted for each pixel during each antenna rotation in the scan-to-scan correlation operation, it is necessary that data to be subjected to this operation be the data obtained as a result of the maximum data sampling operation performed for a given pixel. The data obtained by the maximum data sampling operation are simply written in succession in relevant memory elements in an image memory in the conventional maximum data sampling method and, therefore, it is not necessary in this process to know the timing of completion of the maximum data sampling operation for each pixel. For this reason, it has been impossible to perform the scan-to-scan correlation operation using the data obtained by the maximum data sampling operation even when these operations are carried out by separate processing circuits. Furthermore, the maximum data sampling circuit would require two image memories, which are expensive, to make it possible to perform the maximum data sampling and scan-to-scan correlation operations independently of each other, resulting in an uneconomical circuit configuration.
The other way to improve displayed image quality is to perform pixel data interpolation.
FIG. 41
is a block diagram showing a typical configuration of a conventional radar system.
While rotating at a specific rate in a horizontal plane, a radar antenna
201
transmits short bursts, or pulses, of radio waves at a specific pulse repetition rate and receives an echo signal reflected by targets. A receiver circuit
202
receives and amplifies the signal received by the antenna
201
. An analog-to-digital (A/D) converter
203
converts an analog signal output from the receiver circuit
202
into a digital signal. A primary memory
204
stores A/D-converted data on received echoes for one radial sweep on a real-time basis and serves as a buffer which holds the data to be transferred to an image memory
207
until a new echo signal obtained from a next transmission from the antenna
201
is written. Since the data can not be transferred to the image memory
207
while it is being written into the primary memory
204
in real time, there is provided a secondary memory
205
between the primary memory
204
and the ima
Fujikawa Takumi
Kondo Motoji
Furuno Electric Company Limited
Sotomayor John B.
LandOfFree
Radar and like systems and method for improving image quality does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Radar and like systems and method for improving image quality, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Radar and like systems and method for improving image quality will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2465310