Radar system for collision avoidance

• US 4,403,220 A
• Filed: 04/17/1980
• Issued: 09/06/1983
• Est. Priority Date: 02/05/1980
• Status: Expired due to Term

• Current Assignee: John S. Donovan
• Original Assignee: John S. Donovan
• Inventors: Donovan, John S.
• Primary Examiner(s): Tubbesing, T. H.
• Application Number:
  US06/142,288
• Time in Patent Office: 1,237 Days
• Field of Search: 343/8, 343/112 CA, 343/6 R
• US Class Current: 342/29
• CPC Class Codes: G01S 13/60 wherein the transmitter and receiver are mounted on the moving object, e.g. for determining ground speed, drift angle, ground track G01S13/64 takes precedence
• CPC Class Codes: G01S 13/933 of aircraft or spacecraft

Abstract

A radar system is disclosed adapted to detect relative headings between a system-equipped craft such as aircraft and ships at sea and a detected object moving relative to the ground, the system being particularly adapted to collision avoidance application. The system includes forward and rearward radar transmitter antennas, which are carried by each equipped vehicle. Each of the radar antennas is oscillated in synchronism with the other through a 180° sweep, the forward radar set transmitting a scan spectrum of directional pulses of rf radiation at incremental headings through the sweep. A narrow band pass receiver detects return or echo signals in a very narrow frequency band corresponding to doppler shifted transmission frequencies. The rear radar transmits at a constant frequency and the return signal is utilized to generate a differential frequency which is the end result of a given ground speed and antenna heading. The spectrum scan of the forward transmitter is shifted in accordance with the differential frequency in order to avoid transmitting at ground echo frequency, as well as to narrow the scanning spectrum frequency to provide a highly efficient time and energy utilization in the radar scan.

Claims

1. A craft borne radar system for determination of relative velocity between said craft and relatively moving objects to be detected, said system comprising:

a radar antenna means mounted to said craft;

radar transmitter means causing a sequence of beamed pulses of radio frequency to be transmitted from said radar antenna means, each of said pulses in sequence being of a differing frequency, varying over a scanning frequency spectrum;

receiver means tuned to a narrow frequency band width related to said scanning frequency spectrum such as to correspond to a Doppler shifting of said transmitted frequencies reflected from a detected object moving at a relative velocity such as to shift one or more of said pulse transmission frequencies into said receiver means frequency band width; and

said radar transmitter means causing transmission of a pair of scanning frequency spectrum bands from said antenna means, said bands together constituting said scanning frequency spectrum, each band consisting of sequential pulses each of a frequency varying through a range of frequencies;

said bands being separated by a narrow range of frequencies corresponding to a ground echo signal of a frequency in said receiver means frequency band which would otherwise be reflected from the ground at said receiver means frequency band if transmitted from said radar transmitter means at said narrow band of frequencies for a given groundspeed of said craft;

means for detecting said ground echo signal frequency of said craft as said craft moves at varing groundspeeds;

means for shifting said scanning frequency spectrum of said radar transmitter means in correspondence with the groundspeed of said craft to thereby shift said narrow band of frequencies separating said scanning frequence spectrum bands with varying groundspeed of said radar-carrying craft.

2. The radar system according to claim 1 wherein said radar antenna means comprises a forward facing antenna and includes means for sweeping said radar antenna cyclically along directions generally forward of said craft and wherein said means for detecting said ground echo frequency of said craft includes means for detecting said ground echo frequency with changing antenna heading and wherein said means for shifting said scanning frequency spectrum shifts said narrow band separating said scanning frequency spectrum bands in accordance with the changing ground echo frequency, with changing antenna headings.

3. The radar system according to claim 2 wherein said means for detecting said ground echo frequency comprises a rear radar set means including a rear antenna mounted to said craft and further including means for oscillating said rear antenna in a corresponding sweep to said forward facing antenna in synchronism therewith, and further including a rear radar set transmitter means transmitting radio frequency pulses from said rear radar set antenna;

and means for detecting the Doppler shift of said transmitted rear radar radio wave high frequency pulses from ground echo signals of said rear radar set transmitter means.

4. A method of detecting a relative velocity between a radar-carrying craft and a detected object, the method comprising the steps of:

transmitting high frequency radio wave signals from a swinging radar antenna carried by said craft each in the form of a sequence of pulses, each successive pulse in said sequence varying through a range of frequencies defining a scanning frequency spectrum;

detecting return echo signals from said transmissions with a narrow band pass to a frequency corresponding to return signal echos from transmitted pulses which are shifted in frequency in correspondence with a range of relative velocities between said radar-carrying craft and said detected object; and

shifting said scanning frequency spectrum to decrease the frequencies of each of the pulses in said sequence in accordance with the detected groundspeed and swing of the antenna of said radar-carrying craft such as to increase the maximum rate of relative velocity of detected objects detectable by said range of frequencies in said scanning frequency spectrum with increasing groundspeed thereof and more direct headings therebetween;

whereby higher rates of relative velocity of detected objects may be detected at higher groundspeeds of said radar-carrying craft and more direct headings between said craft and said detected object.

5. The method according to claim 4 wherein said step of transmitting high frequency radio waves from a radar antenna carried by said craft in the form of a sequence of pulses of varying frequencies in scanning frequency spectrum includes the step of transmitting two separate scanning frequency spectrum bands with an intervening frequency band corresponding to a ground echo frequency to which said receiver means is tuned.

6. The method according to claim 5 wherein said step of transmitting two separate scanning frequency spectrum bands includes the step of transmitting said scanning frequency spectrum bands at higher and lower frequencies respectively than said receiver frequency at zero groundspeed of said craft and wherein said step of shifting said scanning frequency spectrum includes the step of, with increasing groundspeeds of said craft, shifting said intervening frequency band in correspondence with the corresponding shift of said scanning frequency spectrum of said transmitted radar pulses, and also includes the step of shifting both of said scanning spectrum frequency bands to be of a lower frequency range in direct correspondence with the ground echo frequency.