Method of and device for removing range ambiguity in a pulse-doppler radar and radar including such a device

• US 4,746,922 A
• Filed: 05/06/1982
• Issued: 05/24/1988
• Est. Priority Date: 05/15/1981
• Status: Expired due to Fees

• Current Assignee: Thomson-CSF
• Original Assignee: Thomson- Csf
• Inventors: Prenat, Michel
• Primary Examiner(s): Tubbesing, T. H.
• Application Number:
  US06/377,451
• Time in Patent Office: 2,210 Days
• Field of Search: 343/7.5, 343/9 R, 343/17.1 PF, 342/88, 342/109, 342/137
• US Class Current: 342/88
• CPC Class Codes: G01S 13/22 using irregular pulse repetition frequency G01S13/12 takes precedence

Abstract

This invention relates to a method of and a device for removing range ambiguity in a pulse Doppler radar and to a radar including such a device especially for missile guidance. On tracking operation at a high pulse repetition frequency the method consists in switching the repetition frequency f_R (k) for each time interval Δt, over a new value f_R (k+1) obtained in a circuit from the measured ambiguous range y(k) and from the ambiguity number n(k), as estimated in a circuit from radar information supplied by the radar, in order to remove eclipsing, to maintain the ambiguity number constant and to estimate the range with a growing accuracy in the course of the tracking operation.

Claims

1. A device for removing range ambiguity in a pulse Doppler radar having a high repetition frequency f_R (k) which varies at times T_k =kΔ

t, where Δ

t is the duration of a measurement cycle, operating in the tracking mode, and including a measurement circuit which supplies the measured ambiguous range corresponding to the repetition frequency f_R (k) and an estimation circuit which supplies an estimation of the ambiguity number and of the radar-to-target range as well as the standard deviation of the error in the estimated range corresponding to the repetition frequency f_R (k), device wherein the repetition frequency is controlled by a servo-loop which, from the measured ambiguous range and from the estimated ambiguity number at the repetition frequency f_R (k) calculates the repetition frequency f_R (k+1) to be used for the following measurement cycle, such that the ambiguity number at f_R (k+1) remains constant, the servo-loop having a transfer function which is of the first order and being composed of the following circuits connected in series;

a first subtraction circuit in which the quantity c/4 f_R (k), is subtracted from the measured ambiguous range supplied by the radar, c being the velocity of the light;

an amplifier having a gain G;

a second substration circuit in which the output signal of the amplifier is reduced by the variation of the radar-to-target range during the time lapse Δ

t, said variation being calculated by a first circuit which multiplies by the duration Δ

t the radial velocity of the target relative to the radar as supplied by the pulse Doppler tracking radar;

a second circuit multiplying the output signal of the second subtraction circuit by a coefficient 1/[n(k)+0.5] calculated by a first calculating circuit supplied with the estimated ambiguity number n(k) corresponding to the repetition frequency f_R (k);

an adding circuit the first input of which receives the output signal of the second multiplying circuit and which delivers a signal equal to c/2 f_R (k+1) and applied to its second input through a delay circuit having a transfer function z^-1 ;

a second calculating circuit supplied with the output signal c/2 f_R (k+1) of the adding circuit and delivering the repetition frequency f_R (k+1) which is supplied to the pulse Doppler radar for the following measurement cycle.

2. A device according to claim 1, wherein the estimation circuit is a Kalman filter supplied with radar information including the radial velocity of the target relative to the radar and the power of the useful signal at the pulse repetition frequency f_R (k) as well as the pulse repetition frequency f_R (k) itself.