Search radar apparatus

• US 4,542,382 A
• Filed: 06/25/1982
• Issued: 09/17/1985
• Est. Priority Date: 07/02/1981
• Status: Expired due to Term

• Current Assignee: Thales Nederland BV (Thales SA)
• Original Assignee: Hollandse Signaalapparaten BV (Thales SA)
• Inventors: Hol, Willem A.
• Primary Examiner(s): Tubbesing, T. H.
• Assistant Examiner(s): Sotomayor, John B.
• Application Number:
  US06/392,115
• Time in Patent Office: 1,180 Days
• Field of Search: 343/7.7, 343/7 A, 343/7.5, 343/7.4
• US Class Current: 342/91
• CPC Class Codes: G01S 13/5248 combining a coherent MTI processor with a zero Doppler processing channel and a clutter mapped memory, e.g. MTD (Moving target detector), area MTI G01S13/538
• CPC Class Codes: G01S 13/538 eliminating objects that have not moved between successive antenna scans, e.g. area MTi

Abstract

Search radar apparatus containing an MTI video processing unit provided with: a canceller for generating video signals of moving targets; a zero-velocity filter for generating clutter video signals; a conditional circuit connected to the canceller and the filter for generating per range quant of each radar scan a clutter switching signal if for the rang quant the signal value obtained with filter is greater than the signal value obtained with the canceller; a combination circuit connected to said filter and the conditional circuit for selecting the clutter video signals present with the clutter switching signals and for determining therefrom a temporary clutter level in each clutter cell and each antenna revolution period; and clutter level indication means connected to the combination circuit for determining a standard clutter level per range-azimuth clutter cell of the radar range with the application of clutter video signals.

Claims

1. Search radar apparatus including an MTI video processing unit having a canceller for generating video signals of moving targets, a zero-velocity filter for generating clutter video signals, and clutter level indication means for determining a standard clutter level per range-azimuth clutter cell of the radar range with the application of clutter video signals, the improvement therein comprising a conditional circuit connected to the canceller and the zero-velocity filter for generating per range quant of each radar scan a clutter switching signal when for the range quant the signal value obtained with the zero-velocity filter is greater than the signal value obtained with the canceller, and further comprising a combination circuit connected to the zero-velocity filter and the conditional circuit for selecting the clutter video signals present with the clutter switching signals and for determining from said selected clutter video signals a temporary clutter level in each clutter cell and in each antenna revolution period for application to the clutter level indication means to produce a standard clutter level.

2. Search radar apparatus as claimed in claim 1, wherein said canceller and said zero-velocity filter function as a linear-phase filter of the transversal type, the weight factors denoted by corresponding numbers being matching to each other in magnitude.

3. Search radar apparatus as claimed in claim 1, wherein said conditional circuit comprises a revaluation circuit connected to the canceller for raising the level of the canceller-supplied video signal, and a comparator for generating a fixed-target indication signal upon receiving simultaneously a clutter signal and a raised video signal to produce a clutter switching signal when the clutter signal exceeds the raised video signal.

4. Search radar apparatus as claimed in claim 3, wherein said radar apparatus is designed to generate transmitter pulses with a plurality of staggered pulse repetition times.

5. Search radar apparatus as claimed in claim 4, wherein said conditional circuit comprises first memory means connected to the comparator for storing per range the quant the fixed-target indication signals for a period corresponding with a number of successive pulse repetition times, and means for generating the clutter switching signal in the presence of a defined minimum number of fixed-target indication signals obtained for corresponding range quants within said period in the memory means.

6. Search radar apparatus as claimed in claim 2, wherein the number of delay lines of the transversal filter with a delay time attuned to the pulse repetition time, is greater than or equal to the real number of weight factors of the filter.

7. Search radar apparatus as claimed in claim 1, wherein said combination circuit comprises selection means and third memory means for storing per antenna revoluton and per clutter cell the maximum value referred to as temporary clutter level of the clutter signals obtained through said selection means, said selection means supplying the third memory means with a clutter signal when the level of the latter clutter signal excess the pregenerated temporary clutter level value of the relevant clutter cell in the presence of the clutter switching signal.

8. Search radar apparatus as claimed in claim 7, wherein said selection means comprise a switching gate for passing the clutter signal under the control of the clutter switching signal;

and a comparator for selecting the greater of the signal passed through the switching gate and the temporary clutter level value supplied by the first memory means for writing into the third memory means.

9. Search radar apparatus as claimed in claim 7, wherein said selection means comprise a comparator for generating a logical switching signal;

an AND gate fed with said switching signal and the clutter switching signal; and

a switching gate fed with the clutter signal and controlled by the AND gate, while the comparator is supplied with the clutter signal and a temporary clutter level value already available in the third memory means.

10. Search radar apparatus as claimed in claim 8 or 9, wherein said switching gate comprises a second input for receiving the already available temporary clutter level value.

11. Search radar apparatus as claimed in claim 8 or 9, wherein said selection means comprises a three-position switching unit for supplying a comparator signal designated as temporary clutter value to the selection means, the switching unit in a first position passes the zero value, in the second position the temporary clutter level value supplied by the first memory means, and in the third position the value supplied by selection means.

12. Search radar apparatus as claimed in claim 11, wherein said radar apparatus comprises a timing unit for setting the three-position switching unit to the first position upon the supply of the clutter signal obtained first in a clutter cell to selection means, to the second position upon the supply of each subsequent clutter signal obtained in the clutter cell having the minimum range value, and to the third position upon the supply of each other clutter signal obtained in the clutter cell.

13. A search radar apparatus as claimed in claim 6, said search radar apparatus generating transmitter pulses of relatively short duration, and further including a search radar apparatus for generating transmitter pulses of a second type, and wherein said search radar apparatuses alternatively generate a transmitter pulse of the second tyep and a series of (N) said transmitter pulses of relatively short duration, the same interval between the instant of generating a transmitter pulse of the second type and that of the next trasmitter pulse of short duriong being a fixed value.

14. Radar apparatus as claimed in claim 13, wherein said transversal filters produce a video signal only once during a period corresponding with the pulse repetition time of the second-type transmitter pulses.

15. Search radar apparatus as claimed in claim 1, wherein said video processing unit comprises a threshold circuit for producing per clutter cell, upon the supply of a clutter video signal and a threshold value obtained from the standard clutter level, a clutter video value in the event said clutter video signal exceeds the standard clutter level.

16. Search radar apparatus as claimed in claim 15, wherein said video processing unit comprises a video selection circuit, connection to the canceller and the threshold circuit, for selecting in magnitude the video signals supplied simultaneously.