Method of measuring distance, notably for short-range radar
The present invention relates to a procedure for measuring distance. It applies notably in respect of short-range radars, but not exclusively. The method uses an electromagnetic wave comprising at least one emission sequence ( 31, 32, 33, 34, 35 ) of the FSK type, at least two emission frequencies (F 1 , F 2 ), emitted successively towards the said target a given number p of times inside the sequence. The gap δF between the emission frequencies (F 1 , F 2 ) is substantially equal to an integer number k of times the repetition frequency (SPRF) of the cycle of frequencies, the distance measurement being obtained on the basis of the measurement of difference of phases Δφ between the signals received corresponding respectively to a first frequency (F 1 ) and to a second frequency (F 2 ).
1. A method of measuring the distance of a target using an electromagnetic wave comprising at least one emission sequence of the FSK type at least two emission frequencies (F 1 , F 2 ) emitted successively towards the said target a given number (p) of times inside the sequence forming a repetition cycle of the emission frequencies (F 1 , F 2 ), the gap (δF) between the emission frequencies (F 1 , F 2 ) being substantially equal to an integer number k, k being greater than or equal to 1, of times the repetition frequency (SPRF) of the cycle of frequencies, the distance measurement being obtained on the basis of the measurement of difference of phases (Δφ) between the signals received corresponding respectively to a first frequency (F 1 ) and to a second frequency (F 2 ).
2. The method according to claim 1 , wherein it comprises a number N of successive emission sequences, N being greater than or equal to two, the pairs of frequencies being defined in such a way that the frequency gaps are different from one pair to another and are an integer multiple of the repetition frequency (SPRF).
3. The method according to claim 2 , wherein the distance measurement is performed on the basis of measurements of phase differences (Δφ) between the signals received originating from the various frequencies (F 1 i , F 2 i ), with F 1,i ≠F 1,j and F 2,i ≠F 2,j , ∀i≠j, of each sequence, the various measurements making it possible to remove the ambiguity in the distance measurement by cross-checking the possibly ambiguous measurements.
4. The method according to claim 3 , wherein the non-ambiguous distance R is obtained by solving the system of inequalities below, on the basis of the measurements of phase differences Δφ i , Δφ j , . . . , Δφ m performed in the sequences of order i, j, . . . , m:
{
Δφ
i
≤
(
(
4
πδ
F
i
c
R
+
ɛ
i
)
mod
2
π
)
)
mod
2
π
Δφ
i
≥
(
(
4
πδ
F
i
c
R
-
ɛ
i
)
mod
2
π
)
)
mod
2
π
{
Δφ
j
≤
(
(
4
πδ
F
j
c
R
+
ɛ
j
)
mod
2
π
)
)
mod
2
π
Δφ
j
≥
(
(
4
πδ
F
j
c
R
-
ɛ
j
)
mod
2
π
)
)
mod
2
π
{
Δφ
k
≤
(
(
4
πδ
F
k
c
R
+
ɛ
k
)
mod
2
π
)
)
mod
2
π
Δφ
k
≥
(
(
4
πδ
F
k
c
R
-
ɛ
k
)
mod
2
π
)
)
mod
2
π
δF i , δF j , . . . , δF m being the frequency gaps between the emission frequencies (F 1 , F 2 ) inside the sequences,
the terms ε i , ε j , . . . , ε m taking into account the errors in the phase difference measurements.
5. The method according claim 3 , wherein a measurement of difference of phases (Δφ) is performed when the power of the received signals is greater than a given threshold.
6. A radar implementing the method according to claim 1 .
7. The radar according to claim 6 , wherein it is fitted to a motor vehicle so as to measure the distance between the carrier vehicle and other vehicles.