1. Field of the Invention
The invention pertains to a radar system having a stabilized display presentation. The invention is particularly useful in marine radar systems having digitized video signals with processing thereof.
2. Description of the Prior Art
Marine radar systems of the prior art have generally operated in the PPI mode using pulsed operation. The repetition rate of the pulses, termed the PRF (pulse repetition frequency), was determined in accordance with an internal oscillator. One PRF triggering pulse was produced for each radar return time or radial scan line.
In the display presentation of the returned radar signals, the sweep starting out from the radar center was commenced by the same PRF triggering pulse or at a fixed time delay thereafter. Unfortunately, a problem arose in that the actual time elapsed between the commencement of the PRF triggering pulse and the emission of a pulse from the radar antenna was subject to variation by a number of factors. As the range of display was changed, the pulse width and average power from the transmitter ouput stage also changed causing the final output tube to fire at different times after the commencement of the PRF pulse depending upon the range chosen by the operator. The problem has been found to be particularly acute when solid state modulators are used. Also, aging of the final output tube or other components in the tramsmitting circuitry caused unwanted variations. Variations could appear between adjacent pulse times as well as between complete sweeps or between ranges.
Because of these variations, an uneven display of received signals was made. The target would tend to appear jagged or be presented out of position upon succeeding sweeps. The jagged edge problem was particularly apparent if digital processing of received signals was employed.
Accordingly, it is object of the present invention to provide a radar system in which the display of received signals is stabilized and synchronized to the actual transmission of radar pulses.
It is also an object of the present invention to provide such a system having a stabilized presentation and further employing digital processing of received radar signals.