Parallel observer spatial evaluator

• US 5,367,303 A
• Filed: 09/17/1993
• Issued: 11/22/1994
• Est. Priority Date: 09/17/1993
• Status: Expired due to Fees

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Alliedsignal Inc. (Honeywell International Inc.)
• Inventors: Waltz, Edward L.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US08/126,961
• Time in Patent Office: 431 Days
• Field of Search: 342/45, 342/46, 342/37, 342/40
• US Class Current: 342/37
• CPC Class Codes: G01S 13/784 Coders or decoders therefor; Degarbling systems; Defruiting systems

Abstract

A method and means for evaluating transponder reply signals in a secondary radar system to differentiate valid replies from false replies. Transponder reply signals received by the interrogating radar are decoded to establish conformity with an established format. All decoded replies to a succession of N interrogation signals are stored in their order of reception in an array of N shift registers. A reply filter is associated with each of the N shift registers. The reply filters operate in parallel to scan the stages of each associated shift register. A unary adder provides the number M of replies detected by the reply filters at each scan step. Reply decision means selects a threshold value that is dependent upon operating conditions of the radar and generates a valid reply signal whenever the value M equals or exceeds the selected threshold value.

Claims

1. The method of evaluating signals received by a secondary radar in response to interrogation signals transmitted by said radar for distinguishing valid replies from false replies, comprising the steps of:

decoding said received signals to establish conformity of said received signals with a predetermined format, said decoded signals conforming with said format constituting reply signals;

storing each of said reply signals received during each of the intervals following N successive interrogation signals, said reply signals being stored in separate storage means for each of said intervals at locations in said storage means corresponding to the times of reception of said replies and being stored for the duration of said N intervals;

scanning said storage means with means for detecting replies stored therein, said scanning being conducted in steps, said detecting means, at each of said scanning steps, contacting in parallel each of said storage locations corresponding to the same time of reply in each of said intervals;

temporarily storing, for a time corresponding to a time duration represented by at least two successive ones of said storage locations, replies detected at each step of said scan;

determining the total number M of said replies detected at each of said scanning steps plus the number of said replies temporarily stored; and

generating a valid reply signal whenever said number M exceeds a predetermined threshold.

2. The method as claimed in claim 1 wherein replies to said interrogation signals are delayed by amounts requested by said interrogation signals and wherein said step of scanning each of said storage means is begun at the storage location within each said storage means corresponding to the amount of delay requested by the interrogation signal eliciting the replies contained in each said storage means.

3. The method as claimed in claim 1, wherein certain of the targets transmitting certain of said replies are moving targets, further including the step of:

shifting replies contained in said selected ones of said storage means from the locations at which said replies were stored to new locations within said selected ones of said storage means, said step of shifting replies being performed prior to performing said scanning step, the changes in locations of said replies being such as to compensate for movement of said targets.

4. Means for evaluating signals received by a secondary radar in response to interrogation signals transmitted by said radar, said evaluating means enabling valid replies to be distinguished from false replies, comprising:

means for decoding said received signals to establish conformity of said received signals with a predetermined format, said decoded signals conforming with said format constituting reply signals;

a plurality N of separate storage means, each of said storage means having a series of storage locations corresponding to increments of time, the replies to each of a succession of N interrogation signals being stored in a separate one of said storage means at locations corresponding to the times of reception of said replies;

a plurality N of reply filters, each of the storage locations of each of said storage means being accessible by one of each of said reply filters;

means in each said reply filter for accessing a selected storage location in said storage means associated with each said reply filter and for providing an output indicating the presence of a reply in each said storage location accessed;

means in each said reply filter for temporarily storing said outputs of said accessing means;

means receiving in parallel from all said reply filters said outputs temporarily stored in said reply filters for determining the number M of said outputs received from said reply filters; and

means for generating a valid reply signal whenever said number M exceeds a predetermined threshold value.

5. Signal evaluating means as claimed in claim 4, with additionally:

means controlling said accessing means of said reply filters whereby said reply filters are caused to access in synchronism successive ones of said storage locations of each of said plurality of N storage means.

6. Signal evaluating means as claimed in claim 5, with additionally:

second means receiving in parallel from all said reply filters said temporarily stored outputs for determining the azimuth of the source of said outputs whenever a valid reply signal is generated for said outputs.

7. Signal evaluating means as claimed in claim 5, wherein certain of said signals received by said radar are transmitted by moving targets, and with additionally:

means associated with each of said plurality of N storage means for shifting the storage locations of the replies contained in selected ones of said storage means to compensate for movement of the targets transmitting the replies contained in said selected ones of said storage means.

8. Means for evaluating signals received by a secondary radar in response to interrogation signals transmitted by said radar, said evaluating means enabling valid replies to be distinguished from false replies, comprising:

means for decoding said received signals to establish conformity of said received signals with a predetermined format, said decoded signals conforming with said format constituting reply signals;

a plurality N of first shift registers, each of said first shift registers having a plurality P of stages corresponding to increments of time, the replies to each of a succession of N interrogation signals being stored in a separate one of said shift registers at stages corresponding to the times of reception of said replies;

a plurality N of reply filters, one each of said reply filters being associated with one each of said shift registers, each of said reply filters including;

multiplex means for accessing selected ones of said P stages of its associated shift register and for providing an output whenever said selected stage contains a reply;

a second shift register having at least two stages for storing said output of said multiplex means; and

means for logically combining the contents of said second shift register into a single reply filter output;

unary adder means receiving in parallel said reply filter output from each of said reply filters for determining the total number M of said reply filter outputs;

means dependent upon operating conditions of said radar for selecting a threshold value; and

means for generating a valid reply signal whenever said number M equals or exceeds said threshold value.

9. Signal evaluating means as claimed in claim 8 wherein certain of the signals received by said radar are transmitted by moving targets, and wherein each of said reply filters further includes:

a third shift register, said third shift register being an up/down shift register having at least P stages, said multiplex means being arranged to access selected ones of said P stages of said third shift register;

means for transferring in parallel the contents of said stages of said first shift register associated with said reply filter to similar stages of said third shift register; and

means for controlling said third shift register to shift the contents thereof up or down to compensate for movement of the source of replies contained in said third shift register.

10. Signal evaluating means as claimed in claim 9 wherein certain of said signals received by said radar contain security delays requested by interrogation signals transmitted by said radar, and wherein each of said reply filters includes:

means for controlling said multiplex means whereby said multiplex means is caused to access selected stages of said third shift register in such order as to compensate for security delays contained in replies stored in said third shift register.