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Title: Method of and apparatus for stabilizing the display rate of permanent echoes in a radar system
Claims: What is claimed is: 1. A method of operating a radar system wherein an input signal from a recurrently swept zone is compared with a threshold and is displayed as an echo pulse upon exceeding said threshold, comprising the steps of: a. establishing a basic threshold for determining the minimum value of an input signal to be displayed; b. updating said basic threshold from step (a) by comparing the input signal of a current sweep with the basic threshold of a preceding sweep of the same zone and incrementing the last-mentioned threshold by a fixed amount of such sign as to maintain said basic threshold close to a clutter level defined by permanent echoes from the swept zone; c. modifying the updated basic threshold from step (b) by algebraically adding thereto a supplemental parameter; d. comparing said input signal with the modified basic threshold from step (c) to detect echo pulses to be displayed; e. determining any deviations of the recurrence rate of said echo pulses from a given standard; and f. varying the value of said supplemental parameter in a sense tending to eliminate said deviations. 2. The method defined in claim 1 wherein the determination in step (e) is carried out by making a first count of the number of echo pulses detected in step (d), concurrently making a second count of the number of times said input signal exceeds a predetermined fixed threshold, registering a positive deviation upon the ratio of said first to said second count exceeding a predetermined upper range limit, and registering a negative deviation upon said ratio falling short of a predetermined lower range limit. 3. The method defined in claim 1 wherein steps (a) through (f) are performed separately for different zones swept in a recurrent cycle. 4. The method defined in claim 1 wherein the input signal in steps (a) and (b) is synthesized from a plurality of different zones swept in the course of a revolution of a radar antenna, steps (c) through (f) being separately performed with individual input signals from said zones. 5. In a radar system having a rotating antenna, receiving means for obtaining from said antenna an input signal resulting from reflected beam energy picked up in a recurrent sweep of a surveyed zone, and indicator means for displaying an echo pulse in response to an input signal exceeding a certain threshold, the combination therewith of: storage means for registering said basic threshold determining the minimum value of an input signal to be displayed; first comparison means connected to said receiving means and to said storage means for generating a first output signal depending upon the relative magnitudes of said input signal and said basic threshold; updating means connected to said first comparison means for incrementing said basic threshold in said storage means by a fixed amount of a sign depending upon said first output signal to maintain said basic threshold close to a clutter level defined by permanent echoes from the swept zone; modification means connected to said storage means for algebraically adding a supplemental parameter to said basic threshold; second comparison means connected to said modification means and to said receiving means for producing a second output signal transmitted to said indicator means upon said input signal exceeding the algebraic sum of said basic threshold and said supplemental parameter; a reference circuit including third comparison means for generating a third output signal upon a deviation of the recurrence rate of said second output signal from a predetermined standard; and control means responsive to said third output signal inserted between said third comparison means and said modification means for varying the value of said supplemental parameter in a sense tending to eliminate said deviation. 6. The combination defined in claim 5 wherein said reference circuit comprises fourth comparison means connected to said receiving means and to a source of fixed threshold for generating a fourth output signal upon said input signal exceeding said fixed threshold, two counters respectively connected to said second and fourth comparison means for providing counts of said second and fourth output signals, and arithmetic means connected to said counters for feeding the ratio of said counts to said third comparison means. 7. The combination defined in claim 6 wherein said third comparison means comprises two comparators connected in parallel to said arithmetic means, said standard being a range of numerical values between a lower limiting value supplied to one of said comparators and an upper limiting value supplied to the other of said comparators, said one of said comparators emitting one type of third output signal upon said ratio falling short of said lower limiting value, said other of said comparators emitting another type of third output signal upon said ratio exceeding said upper limiting value. 8. The combination defined in claim 6 wherein said reference circuit includes step-down means inserted between said fourth comparison means and the associated counter for dividing the recurrence rate of said fourth output signal by a predetermined factor. 9. The combination defined in claim 5 wherein said receiving means is effective to obtain a plurality of input signals from sweeps of different zones during each antenna revolution, said modification means being duplicated for independently establishing said algebraic sum for each of said zones. 10. The combination defined in claim 9 wherein said storage means and first comparison means are common to all the zones, said storage means being connected in parallel to all the duplicated modification means serving said zones. 11. The combination defined in claim 10, further comprising mixer means inserted between said receiving means and said first comparison means for synthesizing a composite signal from all the input signals appearing during each revolution. Other info: Inventors: Busy, Francis (Paris, FR) Application Number: 480145 Filing Date: 1974-06-17 Publication_date: 1976-04-13 Assignee: Thomson-CSF Visualisation et Traitement des Informations (T-VT) (Paris, FR) Primary Class(es): 342/93 Other Classes: US Patent Ref:
Other Refs: Primary Examiner: Tubbesing, T. H. Assistant Examiner: Montone, G. E. Attorney: Ross; Karl F., Dubno; Herbert |
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