Communications: directive radio wave systems and devices (e.g. – With particular circuit – Display
Patent
1992-04-21
1993-12-21
Tubbesing, T. H.
Communications: directive radio wave systems and devices (e.g.,
With particular circuit
Display
342185, G01S 706
Patent
active
052724824
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to radar apparatus.
Conventional modern radar displays generally utilize a cathode-ray tube scanned on a rectangular raster to present an image of the radar return signals, range and bearing markers and graphic information to the user. Where high resolution is required, a 1000 line raster scan is employed. Adjacent pixels along a line of a rectangular raster have the same separation over the entire screen so that the cartesian resolution over the screen is identical, but the bearing resolution is progressively lower towards the radar origin (that is, the radar-carrying ship). In many circumstances, such as when navigating a vessel in open water, this is satisfactory at some distance from the radar origin. There are, however, circumstances in which a greater bearing resolution is required at close ranges, such as when navigating in rivers, canals and estuaries and when berthing. A conventional rectangular raster-scanned radar cannot provide the degree of bearing resolution that is required.
It has been previously proposed to use a spiral-scanned display which has the advantage that the separation between adjacent pixels close to the center of the display, that is, within close range of the radar-carrying vessel, is less than at the edge of the display, because they each subtend the same angle. Such a display should provide a greater resolution in the region where it is of most importance. In practice, however, such spiral-scanned displays have not provided the desired resolution, because very high processor speeds are necessary to handle the data. For example, using a line rotation frequency of 36 KHz with 2048 bits of screen data in one rotation would require a memory read frequency of 73 MHz. To handle data at this frequency would be very difficult and prohibitively expensive in commercial applications.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide radar apparatus with a spiral-scanned or ring-scanned display which avoids the need to process data at very high speeds.
According to one aspect of the present invention there is provided radar apparatus including a display and a memory that stores information about the range and bearing of radar return signals, characterized in that the apparatus includes a deflection circuit that scans the display in successive scans of angular rotation having different radial distances, in that the apparatus reads out from the memory information in respect of alternate pixels, and in that alternate bearing pixels of one scan are interleaved with alternate pixels of the next scan.
In this way the speed of handling the data is half what would otherwise be required.
The deflection circuit preferably scans the display in a spiral scan. The deflection circuit may include two deflection coils, a capacitor connected to each respective coil, a circuit that supplies two sinusoidal signals in phase quadrature to respective ones of the coils, and the coils being resonant. The apparatus preferably reads out information from the memory in the form of plural-bit words with each bit equivalent to two pixels in bearing. The apparatus may include a circuit that blanks out one half of each bit read out from the memory. The blanking circuit may include a digital-to-analog converter.
The memory is preferably divided into two halves, the apparatus supplying radar return signals in respect of alternate pixels to different ones of the two halves of the memory, and the apparatus reading out the contents of one half of the memory during one scan and reading out the contents of the other half during the next scan. The memory may have locations arranged by range and bearing.
The apparatus may include a circuit that rejects radar signals indicative of a radar target in a pixel unless the radar signals also indicate the presence of a target in an adjacent pixel. The circuit may include a comparator and a delay that introduces a delay equivalent to one pixel into the radar signals, the comparator receiving radar signals
REFERENCES:
patent: 3653044 (1972-03-01), Breeze et al.
Blundy Keith J.
Hannah David A.
Smiths Industries Public Limited Company
Tubbesing T. H.
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