Phased array radar system for tracking

• US 6,064,333 A
• Filed: 11/07/1997
• Issued: 05/16/2000
• Est. Priority Date: 05/09/1995
• Status: Expired due to Fees

• Current Assignee: Saab AB
• Original Assignee: Telefonktiebolaget L.M. Ericsson
• Inventors: Stromberg, Dan
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US08/952,119
• Time in Patent Office: 921 Days
• Field of Search: 342/81, 342/90, 342/94, 342/95, 342/96, 342/97, 342/99, 342/107, 342/108, 342/115, 342/135, 342/139, 342/140, 342/157, 342/158, 342/368, 342/371, 342/372
• US Class Current: 342/81
• CPC Class Codes: G01S 13/723 by using numerical data

Abstract

A phased array radar system for target tracking having a track initiation unit, a track prediction unit, a scheduling unit, a track selection unit, and a transmitter/receiver unit. The track initiation unit initiates new tracks representing detected aircraft targets. The track prediction unit predicts the expected position and the calculated position uncertainty of the target as a function of time and the minimal, maximal and optimal time difference to the next measurement. The scheduling unit performs an independent calculation of a sequence of possible time intervals to the next measurement in accordance with specified conditions, and then performs an intersection operation between the calculated sequences of time intervals in order to calculate the optimal time interval to the next measurement. A track selection unit selects that track which has the shortest remaining time interval, K_i, to the next measurement and decreases the time interval to the next measurement for all other tracks with K_i. The transmitter/receiver unit registers an echo from the target and calculates, in a known manner, values for distance, speed, bearing and uncertainty in the distance and speed calculations, which are transferred to the track prediction unit for further calculations.

Claims

1. A phased array radar system for target tracking having a transmitter/receiver unit that forms a waveform and directs a beam toward a target, comprising:

a track initiation unit for initiating new tracks, the track initiation unit connected to a track prediction unit which predicts an expected position and a calculated position uncertainty of the target as a function of time and a minimal, a maximal and an optimal time difference to a next measurement, a scheduling unit connected to the track prediction unit which performs an independent calculation of a sequence of possible time intervals to the next measurement for each one of two conditions, namely that the measurement time difference will be placed between the calculated minimal and maximal time differences and that range-unambiguity will prevail, and then performs an intersection operation between the so calculated sequences of time intervals in order to calculate the optimal time difference to the next measurement, a track selection unit connected to the scheduling unit, which selects that track which has a shortest remaining time interval, K_i, to the next measurement and decreases a time interval to the next measurement for all other tracks with K_i, the track selection unit connected to the transmitter/receiver unit which, after directing the beam, registers an echo from the target and calculates values for distance, speed, and bearing, and for uncertainty in the distance and speed calculations, which values are transferred to the track prediction unit.

2. The radar system according to claim 1, further comprising a resolution unit connected to the scheduling unit for calculating resolution frequencies and possible measurement times for resolution if the scheduling unit is not able to calculate any pulse repetition frequency.

3. The radar system according to claim 1, further comprising a memory unit connected to the track prediction, scheduling, track selection, transmitter/receiver, and track initiation units which stores needed facts for calculations and results of the calculations.

4. The radar system according to claim 3, wherein the scheduling unit calculates the optimal time difference to the next measurement by, firstly selecting a maximal possible pulse repetition frequency (PRF) value among a number of predefined values, secondly calculating that sequence of time intervals for each condition, which covers exactly those time points during which the two conditions are satisfied, thirdly performing an intersection operation on the so calculated sequences of time intervals which generates a time interval sequence N, fourthly calculating a measurement time interval whose length equals a measurement time length, is placed entirely within the time interval sequence N and whose central point lies close to an optimal time point, and fifthly storing a starting time point for the measurement time interval in that cell of the memory unit which stores remaining-time-to-measurement, K_i, in a state vector of track i.

5. The radar system according to claim 4, wherein, if no measurement time interval has been obtained and more PRF values remain, the scheduling unit eliminates a latest selected PRF value, whereafter calculation of the optimal time difference in the scheduling unit is repeated.

6. The radar system according to claim 5, wherein, if no PRF value remains among predefined PRF values, the scheduling unit signals the resolution unit to perform resolution.

7. The radar system according to claim 3, wherein the memory unit contains memory cells which store values for all selectable PRF values, data about an absolute time point for a latest measurement of the radar, data about time interval sequences, and data about a current state of every track including a memory address to a time interval sequence for possible measurement time points and memory cells for the minimal, the maximal and the optimal time differences to the next measurement respectively and remaining-time-to-measurement, K_i.

8. The radar system according to claim 4, wherein the scheduling unit calculates an additional sequence of time intervals for a new condition and performs an intersection operation on this additional time interval sequence and the sequences achieved from the two conditions, where the new condition relates to Doppler blindness avoidance.

9. The radar system according to claim 4, wherein the scheduling unit calculates an additional sequence of time intervals for a new condition and performs an intersection operation on this additional time interval sequence and the sequences achieved from the two conditions, where the new condition relates to cross-over avoidance.

10. The radar system according to claim 4, wherein the scheduling unit calculates an additional sequence of time intervals for a new condition and performs an intersection operation on this additional time interval sequence and the sequences achieved from the two conditions, where the new condition relates to freedom from overlapping.

11. The radar system according to claim 4, wherein the scheduling unit calculates an additional sequence of time intervals for a new condition and performs an intersection operation on this additional time interval sequence and the sequences achieved from the two conditions, where the new condition relates to search.

12. The radar system according to claim 4, wherein the scheduling unit, for all those PRF values that give time interval sequences with at least one time interval of sufficient length, firstly, calculates the length of the measurement time interval, minimum distance to the optimal time point and distance to a Doppler central point, secondly, fuses those values by multiplying an inverted measurement time length with a first weight factor, the minimum distance to the optimal time point with a second weight factor and the distance to the Doppler interval central point with a third weight factor and summing, and thirdly, selects that PRF value which gives a smallest so calculated sum.

13. The radar system according to claim 12, wherein the scheduling unit uses weight factors of 10^-1, 1 and 1 for the first, second and third weight factors, respectively.

14. The radar system according to claim 1, wherein the scheduling unit performs a new series of calculations with parameter values for minimal and optimal time difference set to zero, if the transmitter/receiver unit (4) can not register any echo from the target.

15. The radar system according to claim 14, wherein the track prediction unit changes a track hypothesis between each new measurement.