Communications: directive radio wave systems and devices (e.g. – Return signal controls radar system – Receiver
Patent
1996-03-07
1998-01-13
Sotomayor, John B.
Communications: directive radio wave systems and devices (e.g.,
Return signal controls radar system
Receiver
342 95, 342137, G01S 1356
Patent
active
057084378
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a radar apparatus for the detection of high-speed targets, comprising antenna means, transmitter means for the generation, per antenna direction, of at least M bursts of at least N transmitter pulses with M=2, 3, . . . , N=2, 3, . . . , receiver means for the reception, per transmitter pulse, of a radar echo signal determined per range quant, and a video processor connected to the receiver means, comprising an N-point doppler filter bank for the processing, per burst and per range quant, of the radar echo signals into an N-bin doppler spectrum and a threshold circuit, provided, for each range quant, with N threshold values for the generation of an alarm when crossing of at least one threshold for at least one range quant occurs.
2. Discussion of the Background
A radar apparatus of this kind is known from U.S. Pat. No. 5,049,889. The patent specification discloses a method for generating the N thresholds by means of N cluttermaps divided into range-azimuth cells.
Modern radar systems often are of the 3D type. Thresholding on the basis of cluttermaps would then require a division into range-azimuth-elevation cells which, in addition to a considerable hardware investment, also would claim a considerable portion of the radar system's available time and power budget in order to refresh the contents of the cluttermaps. Particularly, if the radar system is an active phased array type of radar, the overall search volume no longer being cyclically scanned, cluttermap-based thresholding is unattractive.
SUMMARY OF THE INVENTION
The present invention obviates this drawback and is characterised in that the threshold circuit comprises a threshold generator for the generation, per range quant, of N threshold values on the basis of the M doppler spectra.
According to a first embodiment of the invention, it will be possible to detect a high-speed target by applying the lobing effect well-known in the art. This lobing effect will cause the target to disappear periodically as a result of which the thresholds prevailing at the target determined according to the above method will become extremely small, considered in range and frequency. As soon as the target suddenly appears because extinction on account of the multipath effect no longer takes place, a threshold crossing will occur and the target will be detected.
This solution is completely in line with the search behaviour of a phased array radar, which transmits a number of pulse bursts in a generally preselected direction. This solution may, however, also serve a useful purpose in other radar systems, provided these systems allow the transmission of a sufficient number of pulse bursts in a preselected direction. For determining the threshold values it is not required to use all M doppler spectra simultaneously. Instead, it is possible to generate the threshold values on the basis of P doppler spectra obtained from P successive bursts with P=2, . . . , M, the most recently produced doppler spectra generally being used.
An advantageous embodiment of the invention is characterised in that the threshold generator comprises an accumulator for the generation of a mean doppler spectrum on the basis of the P doppler spectra.
In order to obtain a predetermined false-alarm rate, the threshold circuit may include a summator for increasing the mean doppler spectrum thus obtained by an additional threshold value determined per doppler frequency.
For targets approaching at extremely high speeds, the invention shall be further enhanced. As a rule, these are targets having very small radar cross-sections approaching the radar apparatus at speeds of Mach 0.5 to Mach 3. In the first instance, a PRF shall be selected. By tradition, this PRF is selected to be high in order to enable the doppler spectrum to be determined without the occurrence of fold-back. Subsequent thresholding of this doppler spectrum yields an excellent suppression of various types of clutter, such as ground clutter, sea clutter, rain, bi
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Hollandse Signaalapparaten B.V.
Sotomayor John B.
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