Method and apparatus for estimating trajectory

• US 4,751,511 A
• Filed: 05/22/1985
• Issued: 06/14/1988
• Est. Priority Date: 05/24/1984
• Status: Expired due to Fees

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Ueno, Hiroshi, Ohnuma, Tohru, Miyashin, Kiyoshi, Komata, Asao
• Primary Examiner(s): Blum, Theodore M.
• Assistant Examiner(s): Gregory, Bernarr E.
• Application Number:
  US06/736,779
• Time in Patent Office: 1,119 Days
• Field of Search: 343/9 R, 343/10, 343/11 R, 343/16 M, 343/424, 343/463-465, 343/776, 342/59, 342/80, 342/104, 342/105, 342/106, 342/107, 342/109, 342/117
• US Class Current: 342/59
• CPC Class Codes: G01S 13/424 Stacked beam radar
• CPC Class Codes: G01S 13/58 Velocity or trajectory determination systems; Sense-of-movement determination systems
• CPC Class Codes: G01S 13/87 Combinations of radar systems, e.g. primary radar and secondary radar
• CPC Class Codes: G01S 13/88 Radar or analogous systems specially adapted for specific applications electromagnetic prospecting or detecting of objects, e.g. near-field detection, G01V3/00

Abstract

A method and apparatus for estimating the trajectory of a projectile using two interferometric radar antennas each producing a group of interferometric antenna lobes forming intersecting solid angles, and being directed at an elevation angle so that the projectile passes through each interferometric antenna lobe. Each radar antenna transmits a different frequency of pulsed RF power and receives pulsed RF signals reflected from the projectile whenever the projectile passes through the antenna lobes of the radar antennas. Based on the received signals of respective radar antennas, the range and time information for the projectile passing through the antenna lobes of the respective radar antennas can be obtained. From this range and time information, the three-dimensional coordinates, speed and acceleration at the points in the antenna lobes through which the projectile passes can be obtained. From the 3-dimensional coordinates and the speed and acceleration of the projectile, the trajectory of the projectile can be estimated.

Claims

1. A method for detecting a projectile using a radar system, said method comprising the steps of:

(a) generating a first group of fan-shaped interferometric antenna lobes such that said first group of lobes defines a first continuous surface including solid angles of each of said first group of lobes;

(b) generating a second group of fan-shaped interferometric antenna lobes such that said second group of lobes defines a second continuous surface including solid angles of each of said second grup of lobes and so that said solid angles of said first group of lobes intersect said solid angles of said second group of lobes;

(c) elevating said solid angles at an angle from the ground at a point where the radar system is located;

(d) detecting the projectile as it penetrates at least one of said antenna lobes by receiving at least one radar echo signal reflected from the projectile;

(e) measuring the distances between the radar system and two points in respective antenna lobes through which the projectile passes;

(f) obtaining the times at which the projectile passes through said two points; and

(g) obtaining the speed and acceleration of the projectile as it passes through said two points.

2. A method for estimating the trajectory of a projectile using a radar system, said method comprising the steps of:

(a) generating a first group of fan-shaped interferometric antenna lobes using a first interferometric antenna and a first RF signal, such that said first group of lobes defines a first continuous surface including solid angles of each of said first group of lobes;

(b) generating a second group of interferometric antenna lobes using a second interferometric antenna and and second RF signal different than said first RF signal, such that said second group of lobes defines a second continuous surface including solid angles of each of said second group of lobes, and so that said solid angles of said first group of lobes respectively intersect solid angles of said second group of lobes;

(c) elevating said solid angles at an angle from the ground at a point where the radar system is located;

(d) receiving RF signals reflected from the projectile as the projectile penetrates said first group of lobes and said second group of lobes;

(e) measuring distances between said first and said second interferometric antennas and points in said first and said second groups of antenna lobes through which the projectile passes;

(f) obtaining time information for the projectile as it passes through each of said points;

(g) obtaining the speed and acceleration of the projectile as it passes through each of said points; and

(h) estimating the three-dimensional trajectory of the projectile using said distances, said speed and acceleration, said elevation angle and said intersection angle of said solid angles of the respective antenna lobes for each of said first and second groups of antenna lobes.

3. An apparatus in a radar system for estimating the trajectory of a projectile, comprising:

first interferometric antenna means for transmitting and receiving a RF signal, and for providing a first group of interferometric antenna lobes, each including a solid angle;

second interferometric antenna means for transmitting and receiving a RF signal, and for providing a second group of interferometric antenna lobes, each including a solid angle,

each of said first and second interferometric antenna means including two antenna elements arranged so that;

(1) the antenna patterns for each element overlap, (2) the distance D (mm) between the antenna elements satisfies γ

=λ

/D where γ

(radian) corresponds to an angle between respective lobes in said first and second groups of interferometric antenna lobes, and λ

(mm) is the wavelength of the respective RF signals transmitted by said first and said second antenna means, and (3) said solid angles of said first and said second groups of interferometric antenna lobes intersect at an intersection angle and said first and said second antenna means being elevated by an elevation angle;

first and second RF transmitter means, respectively connected to said first and said second interferometric antenna means, for transmitting the respective RF signals in accordance with a pulse repetition rate control signal, each RF signal having a different frequency;

first and second RF receiver means, respectively connected to said first and said second interferometric antenna means, for detecting RF signals received by respective ones of said first and said second interferometfic antenna means and for converting said received signals into pulsed video signals, said RF signals received by said first and said second interferometric antenna means corresponding to RF signals reflected from the projectile;

signal processor means for providing the pulse repetition rate control signal, for calculating range signals corresponding to the distance between said antenna elements and points in said first and second groups of interferometric antenna lobes through which the projectile passes, and for providing time information associated with the projectile passing through each of the points in said first and said second groups of interferometric antenna lobes;

three -dimensional data computing means for computing three-dimensional coordinates for each of said points using the range signals, said elevation angle and said intersection angle; and

trajectory estimating means for computing a continuous three-dimensional trajectory extending through each of said points, using the computed three-dimensional coordinates of each of said points and said time information.

4. The apparatus according to claim 3, further comprising:

first hybrid coupler means, operatively connected between said first interferometric antenna means, and said first RF transmitter means and said first RF receiver means, for dividing the RF signal into half and applying each half to respective ones of said antenna elements of said first antenna means, and for combining the RF signals received by each of said two antenna elements of said first antenna means;

first circulator means, operatively connected between said first hybrid coupler, and said first transmitter means and said first receiver means, for channeling said RF signal from said RF transmitter to said first interferometric antenna means, and for automatically channeling said RF signal from said first hybrid coupler to said first RF receiver means;

second hybrid coupler means, operatively connected between said second interferometric antenna means, and said second RF transmitter means and said second RF receiver means, for dividing the RF signal into half and applying each half to respective ones of said antenna elements of said second antenna means, and for combining the RF signals received by each of said two antenna elements of said second antenna means; and

second circulator means, operatively connected between said second hybrid coupler, and said second transmitter means and said second receiver means, for channeling said RF signal from said RF transmitter to said second interferometric antenna means, and for automatically channeling said RF signal from said second hybrid coupler to said second RF receiver means.

5. The apparatus according to claim 4, wherein each of said antenna elements comprises a horn antenna element.

6. The apparatus according to claim 3, wherein each of said antenna elements comprises a horn antenna element.