George B Litchford

40273075, May 31, 1977

May 9, 1975

5/576143

George B. Litchford - Northport NY

Litchstreet Co. - Northport NY

G01S 956

343 65LC

Proximity indication and evaluation of mobile vehicles, using the signals emitted by the hundreds of existing secondary radar ground stations and the nearly 100,000 cooperating transponders on the vehicles, to detect intrusion in a monitored proximity volume and to determine slant range and/or relative bearing to the intruder.

41157710, Sep 19, 1978

May 17, 1977

5/797675

George B. Litchford - Northport NY

Litchstreet Co. - Northport NY

G01S 956

343 6R

A virtual secondary surveillance radar (SSR) is provided at any desired location within the coverage area of an actual SSR by receiving the interrogations from the actual SSR and the transponder replies thereto. The received signals are processed to yield information as to the positions of the transponders with respect to the desired location, simulating the performance of an actual SSR at that location. BACKGROUND.

51988232, Mar 30, 1993

Dec 23, 1991

7/813137

George B. Litchford - Northport NY
John Keller - Huntington NY

Litchstreet Co. - Northport NY

G01S 502
G01S 1300
G01S 504

342429

The range from which transponder replies can be received at a virtual secondary surveillance radar of the type described in U. S. Pat. No. 4,115,771 is extended by replacing the omnidirectional antenna previously utilized to receive replies from transponders within the range of the SSR with a stationary array of a plurality of directive antennas arranged in a circle and having radiation patterns pointing in different directions from the center of and covering a respective sector of the circle, and sequentially switching on the antenna of the array covering the sector in which the rotating beam of the associated SSR is then pointing. In an arrangement in which the SSR and PSSR are so widely separated that in certain pointing directions the SSR beam overlies more than one sector of the antenna array, the antennas are sequentially switched on at calculated switching times determined from the pointing direction of the SSR beam and the times it takes in the geometrical arrangement between the SSR beam and the radiation patterns of the antennas of the array, for a given SSR interrogating pulse to propagate, from launch, along the beam until it reaches the line separating the first encountered sector from the next adjacent sector, between second and third sectors, and so on, such that a high gain directive antenna is always pointing in the proper direction to receive reply signals from a transponder intercepted by the scanning beam of the SSR.

44867557, Dec 4, 1984

Feb 22, 1982

6/351275

Burton L. Hulland - Glenwood Landing NY
George B. Litchford - Northport NY

Litchstreet Co. - Northport NY

G01S 1378

343 65LC

A threat warning collision avoidance system at an Own station that produces pseudo range data, identity and, when available, differential altitude data from standard ATCRBS interrogations and Other station's replies, rejecting the identity and data from Other stations that are outside a proximity space surrounding Own station, and producing a threat alert signal and displaying the identity and associated data of any Other station entering said proximity space.

39597938, May 25, 1976

Aug 7, 1974

5/495271

George B. Litchford - Northport NY

Litchstreet Co. - Northport NY

G01S 956

343 65R

A method and apparatus for determining the distance to a secondary surveillance radar (SSR) station from an own transponder station when another transponder station lies within a monitored region surrounding the own station. The distance information is utilized to modify the operating mode of a proximity indicating system at the own station.

46426485, Feb 10, 1987

Mar 14, 1984

6/589524

Burton L. Hulland - Glenwood Landing NY
George B. Litchford - Northport NY

Litchstreet Co. - Northport NY

G01S 302

342455

A simple active/passive proximity warning system for an Own station that uses differential time of arrival values, direct time of arrival values, and differential altitude values determined from 1030 MHz interrogations from ground-based SSRs and Own station and 1090 MHz transponder replies from Other stations to identify threats is disclosed. The invention combines a passive detection system and an active detection system into an integrated system that overcomes the limitations present when either type of system is used by itself. Generally speaking, the passive system identifies threats and produces a threat alert when the differential altitude value and the largest time of arrival value associated with an Other station are below predetermined values. A preferred embodiment of the active system monitors the environment for SSR density, classifies the environment into a plurality of "cases", and automatically selects in response thereto one of a plurality of control modes. The control mode selected determines in whole or in part whether interrogations will be produced by an interrogator in the active system, and the rate at which they are produced.

47898658, Dec 6, 1988

Oct 21, 1987

7/111812

George B. Litchford - Northport NY

Litchstreet Co. - Northport NY

G01S 302
G08G 702

342455

The operation of a positive finding collision avoidance system at an Own station that determines Own's and Others' positions from SSR interrogations and replies thereto is initialized by briefly transmitting interrogations from Own station and receiving non-garbled replies thereto from Other stations to determine their direct ranges from Own. The range data is used in a trigonometric computation to obtain Own's and such Others' initial positions. Interference with the normal operation of the standard ATCRBS is limited to a minimum by transmitting from Own very briefly and only when necessary. The distance between pairs of SSRs is also computed.

40218023, May 3, 1977

Jul 29, 1975

5/599961

George B. Litchford - Northport NY

Litchstreet Co. - Northport NY

G01S 956

343 65LC

A collision-predictive CAS at a protected station or vehicle that produces TAU data relating to differential azimuth and/or TOA from standard ATCRBS interrogations and replies, and selects the largest closing TAU signal of a threatening Other station to provide reliable warning while minimizing false alarms. Similarly processed differential altitude information provides a further criterion. Multiple radar environments enable production of additional sets of TAU values and increased discrimination against false alarms.