# US 12,181,565 B2 · Aviation detect and avoid method and system

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- Number: US 12,181,565 B2
- Document ID: US12181565B2
- Status: Granted
- Kind: B2
- Application number: 17/577,250
- Filed: 2022-01-17
- Published: 2022-05-05
- Granted: 2024-12-31
- Earliest claimed: 2018-02-14
- Assignees: Seamatica Aerospace Ltd.
- Applicants: Seamatica Aerospace Ltd.
- Inventors: Yake Li; Siu Donald O'Young; Maged E. Beshai
- Web page: https://patentgrep.com/patent/US12181565B2

## CPC

- G01S 13/781: {Secondary Surveillance Radar [SSR] in general}
- G01S 13/003: {Bistatic radar systems; Multistatic radar systems}
- G01S 13/762: {with special measures concerning the radiation pattern, e.g. S.L.S. (aerials or aerial systems providing at least two radiation patterns, e.g. providing sum and difference patterns, H01Q25/00)}
- G01S 13/933: of aircraft or spacecraft
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES

## Abstract

A detect-and-avoid system for an ownship aircraft is disclosed. The system has a control station in communication with an ownship aircraft, and a Passive Secondary Surveillance Radar (PSSR) system at the ownship aircraft. The PSSR is equipped to receive a reply from a target object, in response to an interrogation signal of staggered P1 and P3 pulses sent by a narrow-beam antenna of a Secondary Surveillance Radar (SSR) to the target object, and also to receive P2 pulses transmitted by a wide-beam antenna of the SSR. A pulse repetition frequency (PRF) pattern for the staggered interrogation signal is determined, followed by estimating a transmit time of the interrogation signal, and determining a position of the target object. A corresponding detect-and-avoid method is also disclosed.

## Claims

### Claim 1

A method for detecting and avoiding a target object, comprising:
determining a position of the target object, comprising:
at a Passive Secondary Surveillance Radar (PSSR) spaced apart from a Secondary Surveillance Radar (SSR):
determining a pulse repetition frequency (PRF) pattern for staggered interrogation pulses (P1, P2, P3) of a Secondary Surveillance Radar (SSR), the P2 and P3 pulses being synchronized to respective P1 pulses with respective first and second predefined time gaps;
receiving a reply from the target object in response to an interrogation signal comprising a P3 pulse sent by the SSR to said target object;
estimating a transmit time of said P3 pulse of the interrogation signal based on a reception time of said reply, and the PRF pattern; and
determining the position of the target object using an altitude information h of the target object contained in said reply, a location of the SSR, said estimated transmit time of said P3 pulse of the interrogation signal, and said reception time of said reply;
said determining said PRF pattern comprising:
during a time-window where the PSSR is within range of a wide-beam antenna of the SSR:
detecting successive P2 pulses;
forming a time-ordered sequence of intervals separating the successive P2 pulses;
identifying at least two successive congruent segments of the time-ordered sequence;
determining a pulse repetition pattern of P2 pulses as one of the segments subject to the constraint that a number of intervals of said one of the segments is within an initial length lower bound and a predefined length upper bound;
deriving the PRF pattern based on the pulse repetition pattern of P2 pulses and corresponding values of the first and second predefined time gaps;
and
controlling the target object so as to avoid the target object.

### Claim 2 (depends on 1)

The method of claim 1 further comprising:
during a time-window where the PSSR is within range of a narrow-beam antenna of the SSR:
detecting P1 and P3 pulses; and
determining a value of the second predefined time gap between P3 and P1 pulses, thereby determining an interrogation mode of the SSR.

### Claim 3 (depends on 1)

The method of claim 1 wherein said forming comprises:
initializing an array of said intervals and
initializing a first pointer of said array.

### Claim 4 (depends on 1)

The method of claim 1 wherein said identifying comprises:
finding a primary string of adjoining intervals, of said time-ordered sequence, in which a first interval is distinct from any other interval with a last interval preceding an interval that equals said first interval;
examining a candidate string of adjoining intervals of maximum congruence to said first string, following said last interval; and
subject to a determination that said candidate string is fully congruent with said first string, determining said first string as said PRF pattern.

### Claim 5 (depends on 4)

The method of claim 4 further comprising, subject to a determination that said candidate string is not fully congruent with said first string:
appending said candidate string to said primary string; and
updating said last interval to be the end interval of the candidate string.

### Claim 6 (depends on 4)

The method of claim 4 further comprising continually storing said primary string and said candidate string in said array.

### Claim 7 (depends on 4)

The method of claim 4 further comprising terminating said determining of the PRF pattern subject to a determination that at least one of said primary string and candidate string comprises a number of intervals exceeding said predefined length upper bound.

### Claim 8 (depends on 1)

The method of claim 1 further comprising:
using said pulse repetition pattern of P2 pulses as a reference string, and a number of intervals of the reference string as a reference length;
continuing to receive P2 pulses;
forming consecutive strings of intervals between successive pulses, each consecutive string comprising a number of intervals equal to the reference length;
determining a number of consecutive strings that are congruent with the reference string; and
subject to a determination that said number of consecutive strings at least equals a predefined congruence lower bound, ascertaining correctness of detected pattern.

### Claim 9 (depends on 8)

The method of claim 8 further comprising, subject to a determination that said number of consecutive strings is less than said congruence lower bound:
resetting said initial length lower bound to a higher value not exceeding said predefined length upper bound; and
repeating said determining said PRF pattern.

### Claim 10 (depends on 8)

The method of claim 8 wherein said determining a number of consecutive strings that are congruent comprises sequentially determining congruence of two successive strings, starting with said reference string.

### Claim 11 (depends on 10)

The method of claim 10 wherein said determining congruence comprises:
determining a respective absolute value of a difference between each interval of one of the strings and an interval of a corresponding positions of the other string; and
ascertaining congruence subject to a determination that said respective absolute value is below a first prescribed tolerance level.

### Claim 12

A detect-and-avoid system for an ownship aircraft comprising:
a control station in communication with an ownship aircraft for controlling the ownship air-craft;
at the ownship aircraft, a Passive Secondary Surveillance Radar (PSSR) system in communication with the control station, the PSSR comprising:
a first receiver for receiving a reply from a target object wherein said reply is responsive to an interrogation signal comprising P1 and P3 pulses sent by a narrow-beam antenna of a Secondary Surveillance Radar (SSR) to said target object;
a second receiver for receiving a stream of P2 pulses from the SSR, said P2 pulses being transmitted in a staggered pattern by a wide-beam antenna of the SSR;
a first processor coupled to said first receiver and said second receiver,
a second processor for executing instructions to:
determine a pulse repetition frequency (PRF) pattern for staggered interrogation pulses (P1, P2, P3) of the SSR, the P2 and P3 pulses being synchronized to respective P1 pulses with respective first and second predefined time gaps;
estimate a transmit time of said interrogation signal based on a reception time of said reply, and the PRF pattern;
determine the position of the target object based on an altitude information of the target object provided in said reply, a location of the SSR, said transmit time of said interrogation signal, and said reception time of said reply; and
during a time-window where the PSSR is within range of the wide-beam antenna:
detect successive P2 pulses;
form a time-ordered sequence of intervals separating the successive P2 pulses;
identify at least two successive congruent segments of the time-ordered sequence; and
determine a pulse repetition pattern of P2 pulses as one of the segments subject to the constraint that a number of intervals of said one of the segments is within predefined lower and upper bounds.

### Claim 13 (depends on 12)

The detect-and-avoid system of claim 12 wherein said instructions further cause the second processor to:
during a time-window where the PSSR is within range of the narrow-beam antenna:
detect P1 and P3 pulses; and
determine a value of the second predefined time gap between P3 and P1 pulses, thereby determining an interrogation mode of the SSR; and
derive the PRF pattern based on the pulse repetition pattern of P2 pulses and corresponding values of the first and second predefined time gaps.

### Claim 14 (depends on 12)

The detect-and-avoid system of claim 12 wherein:
the first processor continually determines inter-pulse intervals and stores the intervals in a buffer; and
the second processor independently reads individual inter-pulse intervals and executes said instructions,
thereby decoupling pulse acquisition and inter-pulse measurement timescale from processing timescale.

### Claim 15 (depends on 12)

The detect-and-avoid system of claim 12 wherein said second processor is configured to ensure that a mean execution time per interval does not exceed a mean inter-pulse interval.

### Claim 16 (depends on 12)

The detect-and-avoid system of claim 12 further comprising ground-based PSSR equipment installed within a ground-based surveillance system, said PSSR equipment being communicatively coupled to respective interface equipment within said control station.

### Claim 17 (depends on 14)

The detect-and-avoid system of claim 14 further comprising a comparator unit communicatively coupled to said respective interface, the comparator unit comprising a respective processor configured to:
receive data relevant to safety of the ownship generated at the PSSR system of the ownship;
receive data relevant to safety of the ownship generated at the ground-based PSSR equipment;
perform comparative data analysis to enhance safety measures.

### Claim 18 (depends on 12)

The detect-and-avoid system of claim 12 wherein said instructions further cause the second processor to:
during a time-window where the PSSR is within range of the narrow-beam antenna:
initialize an array of said intervals; and
initialize a first pointer of said array.

### Claim 19 (depends on 12)

The detect-and-avoid system of claim 12 wherein said instructions to identify further cause the second processor to:
during a time-window where the PSSR is within range of the narrow-beam antenna:
find a primary string of adjoining intervals, of said time-ordered sequence, in which a first interval is distinct from any other interval with a last interval preceding an interval that equals said first interval;
examine a candidate string of adjoining intervals of maximum congruence to said first string, following said last interval; and
subject to a determination that said candidate string is fully congruent with said first string, determining said first string as said PRF pattern.

### Claim 20 (depends on 12)

The detect-and-avoid system of claim 12 wherein said instructions further cause the second processor to:
during a time-window where the PSSR is within range of the narrow-beam antenna:
use said pulse repetition pattern of P2 pulses as a reference string, and a number of intervals of the reference string as a reference length;
continue to receive P2 pulses;
form consecutive strings of intervals between successive pulses, each consecutive string comprising a number of intervals equal to the reference length;
determine a number of consecutive strings that are congruent with the reference string; and
subject to a determination that said number of consecutive strings at least equals a predefined congruence lower bound, ascertaining correctness of detected pattern.