GB2251748A

GB2251748A - Measurement of the spatial delay between two signals of the same frequency.

Info

Publication number: GB2251748A
Application number: GB8407526A
Authority: GB
Inventors: Claude Aury; Jean-Luc Montardy
Original assignee: Thomson CSF SA
Current assignee: Thales SA
Priority date: 1983-03-31
Filing date: 1984-03-22
Publication date: 1992-07-15
Anticipated expiration: 2004-03-22
Also published as: FR2661507A1; FR2661507B1; GB2251748B; IT1235232B; IT8467306A0; NL8401024A; DE3411653A1

Description

PROCESS AND DEVICE FOR THE MEASUREMENT OF THE SPATIAL DELAY BETWEEN TWO SIGNALS OF THE SAME FREQUENCY ESPECIALLY IN THE MICROWAVE BAND The present invention relates to a process and a device for the measurement of the spatial delay between two signals of the same frequency, especially in the microwave band.

A device of this type is used, for exampLe, in a phase direction finder whose schematic diagram is illus- trated by the attached Figure 1, and which seeks to determine the angle of the front P of a wave, relative to a reference plane, in order to determine the relative direction of the transmitter of this wave.

Spatial delay S is used to designate the difference in the paths traversed by two points P1 and P2 of the front of the transmitted wave before reaching the reference plane. As illustrated by Figure 1, there are two receiving antennae, A1 and A2, separated by a distance d and situated in a plane constituting the reference plane. The front P of the received wave makes an angle 0 with the said reference plane. The spatial deLay S is also shown by the distance (A1P1) of the first antenna A1 to the front P when this latter reaches the second antenna A2 (A2P2=O).

A first relationship (1) links the spatial delay S to the distance d of the antennae: S = d.sin F (1) The spatial delay S is also defined from the relative phase t and frequency f, to which the wavelength of the two signals r1 (t) and r2 Ct) received by antennae A1 and A2 respectively corresponds. The spatial delay S is in effect defined by the relationsh;D (2)

in which c is the speed of light.

Conventional phase direction finders are equipped with a device 1 which measures the relative phase i of the signals received respectively by the two antennae A1 and h2, and also measures the frequency f. It is then necessary to calculate the spatial delay S using relationship (2) which makes it possible to know the direction of arrival of the transmissions by using relationship (1). -This direction of arrival G can thus onLy be known after the measurement of the frequency f of the received signals.

In the microwave field, for example, the phase is measured with the aid of phase discriminators issuing signals whose relative amplitude is linked to phase by a known law. In the same way, frequency f can be measured with the aid of another phase discriminator whose phasefrequency law is known. But the prior knowledge of frequency involves the necessity for specialised circuits, which has a significant disadvantage within the compass of apolications of the phase direction finder, especially in the case of operation over a very wide band.

The present invention makes it possible to overcome the aforementioned disadvantages.

It consists of using relative phase properties of two signals of the same frequency propagating in opposite directions, which makes it possible to measure, over a wide frequency band, the spatial delsy of the two signals without the need to measure or to know their frequency.

According to the invention, the process of measurement of'the spatial delay between two incident signals of the same frequency comprises the following successive stages: - injection of the two signals at the input of a transmission unit in such a way that they propagate in opposite directions in the transmission unit; - determination of a reference distance relative to one of the injection points, for which the electrical paths traversed respectively in the transmission unit by the two signals from their injection point are equal; - generation of the envelope of the resultant wave existing in the transmission unit;; - measurement of the gap separating the reference distance and the position of maximum envelope amplitude closest to the said reference distance and computation of the spatial delay which exists between the two incident signals of the same frequency at the input to the transmission unit and which is equal to twice the calculated gap.

Another advantage of the present invention is that it also makes it possible to measure the frequency of the said signals, it being possible to make this measurement alone or in parallel with the measurement of spatial delay.

Another advantage of the present invention is to make possible the calculation of the spatial delay which exists between two complex signals composed of the same plurality of elementary signals of different frquencies.

Other advantages anc characteristics of the present invention will become apparent from reading the detailed description which follows with reference to the annexed figures which represent: - Figure 1, the schematic diagram of a phase direction finder, already described in the introduction; - Figure 2, the block diagram of the device according to the invention; - Figure 3, an embodiment of one part of the device of Figure 2; - Figure 4, one embodiment variant of the part of the device according to the invention represented by Figure 3; and - Figure 5, another embodiment variant of the part of the device according to the invention represented by Figure 3.

Figure < represents the block diagram of the device according to the invention. The two signals of the same frequency f, to which the wavelength ss corresponds, are appLied to the first and second input A and B respectively of transmission unit 2 and prcpagate in opposite directions.

Transmission unit 2 may be transmission lines (such as those represented in Figures 3, 4, 5 for example) or more localized circuits (not represented).

Mo designates the reference point which is situated at the so-called reference distance from an injection point, A for example, and for which the electrical paths traversed by the two incident signals are equal.

The signal issued by the transmission unit 2 is applied to the input of a circuit 3 determining the envelope of the signal applied to its input.

A calculation circuit 4 determines the distance so of the first maximum value of the envelope, determined by circuit 3, from the reference point Mo of transmission unit 2. It also calculates the spatial delay S which is equal, as will be shown later, to twice the distance so and possibly the direction 0 of the wave front if the two signals applied to the input of the transmission unit 2 have come from this wave front.

If it is wished to measure the frequency of the two incident signals, a circuit 5 calculates the frequency f of the input signals of the device from the distance separating two successive maxima of the envelope of the resultant signal existing in the transmission unit 2. The methods of calculation are described later.

The operation of the device according to the invention represented by Figure 2 is described below with reference to Figures 2 and 3.

A first embodiment of the transmission unit 2 and of the circuit 3 for determining the envelope is represented by Figure 3.

The transmission unit 2 consists, for example; of a simple transmission line 200 at the two ends A and B of which are applied respectively the two incident signals of frequency f.

The simultaneous presence of the two signals on the same line creates a standing wave condition.

As has already been stated, the present invention is based upon the use of the relative phase properties of two signals of the same frequency propagating in opposite directions in a transmission unit, and so the remaining processing is carried out on the resultant standing wave.

According to one non-limiting embodiment, the generated standing wave is sampled by N means of coupling 201, 202, ..., 20N. It is assumed that the couplings are weak, in order not to interfere with the standing condition.

Circuit 3 which computes the envelope of the standing wave may be composed in a non-limiting way of N detectors 301, 302, ..., 30N corresponding respectively to means of coupling 201, 202, ..., 20N and each issuing a sample of the envelope of the standing wave. The number and positioning of the means of coupling 201, 202, ..., 20N are defined by those skilled in the art, using Shannon's theorem, in such a way as to reconstitute at the output of detectors 301, 302, ..., 30N, in the operating frequency band, the envelope of the standing wave.

The detected samples issued by the N detectors 301, 302, ..., 30N are applied to the input of a space-time conversion device 31 which issue at a first output 311 a periodic signal Sp which represents the sampled variations of the output voltages of the N detectors, that is to say the envelope variations of the standing wave created in the transmission unit 2. At a second output 312 the spacetime conversion device 31 issues a space-time reference signal SR. The detectors are preferably quadratic detectors. The conversion device may be, according to one nonlimiting example which is not represented, an N-input commutator receiving respectively the output signals of detectors 301, 302, ..., 30N and switching- them in sequence onto the first output 311 at a controlled rate determined by an exterior pulsed signal.The reference signal SR is, in this case, a signal which represents the position of each sample taken and detected relative to the reference distance and is obtained by a generator circuit (not represented) from the control pulse signal and from the known distribution of the N means of coupling 201, 202, ..., 20N along transmission unit 2.

It is also possible to use the output voltages of the parallel detectors in an instantaneous fashion in order to obtain the rapid development of the measured magnitude or magnitudes such as, for example, in a pulse compression radar, of the variation of HF frequency within one pulse.

The simultaneous presence of the two signals on the same line, as is the case in the embodiment of Figure 3, creates a standing wave condition. Point Mo chosen as reference is then the mid-point of the transmission line 200.

The phase displacements experienced by each of the two input signals between the respective input A or B and the reference point Mo of the transmission line are equal and consequently their relative phase displacement at the reference point Mo is the same as their relative phase dis placement j at the input of the transmission line 200.

At each point of the transmission line situated at a distance s from the reference point Mo, the voltage e(s) which s created is expressed by the relationship (3):

where - E is a voltage which is a function of the amplitude of the signals injected at each end of the line; - { is the phase difference of the two input signals of the transmission line; and - = c and a = 2 tr .f are the wavelength and C the pulse rate of the input signals respectively.

It has been assumed that the coupling means 201, 202, ..., 20N are designed in such a way as not to interfere with the created standing wave.

The voltage E(s) detected along the line by quadratic detectors is proportional to

The voltage maxima along the line are produced at points a distance s from the reference point Mo, such that:

where k is a relative number.

The distance s of the maxima may thus be expressed as a function of the phase displacement , of the wavelength 7 and of k by. the relationship (5) s=. -k 2 If the quantity # .# (6) is designated by so, the distance s of the maxima irom the mid-point or reference point Mo of the line is given by

modulus #/2 (7) Now, in the introduction to the description the spatial delay S was defined by the relationship (2) O = 2 S Comparison of relationships (2) and (6) makes it possible to express the spatial delay S as a function of the distance so of the first maximum to the reference point Mo by the following equation (8):: S = 2.so (8) The spatial delay S, or path difference traversed by the two input signals before being injected into the transmission line 200 is thus given by the equality (8) which is independent of the wavelength /r and consequently of the frequency f of the input signals.

Circuit 4 of Figure 1 thus measures the distance so of the first maximum close to reference point Mo, then calculates the spatial delay S = 2.so. It also calculates the direction 0 of the wave front from the relationship (1) shown in the introduction to the description, S = d.sin F (1) or again 0 = Arc sin s/d (1b) if it is assumed that the two signals injected at the inpJts A and B of the transmission means 2 come from the same wave, that the distance d separating the two receiving anternae A1 and A2 (Figure 1) is known and that the electrical paths linking antennae A1 and A2 to the inputs A and B respectively of the transmission unit 2 are equal.

The relationship (7) mentioned above indicates the position s of the maxima of the envelope of the resultant signal transmitted by the transmission unit 2 s = so Cmodulus 2 The distance & s between two successive maxima is thus equal to A s = 2 and is consequently directly proportional to the wavelength of the two incident signals and equal, except for a coefficient c, to the inverse of the frequency f of the incident signals.

By determining the interval- A s separating two suc- cessive maxima, circuit 5 makes it possible to calculate c the frequency f - 2. 5- s Calculation of the spatial delay by circuit 4 and of the frequency f by circuit 5 may be carried out independently of each other. The two circuits 4 and 5 may thus exist together or separately in the device according to the invention.

If the input signals are complex signals, that is to say composed of the same plurality of elementary signals of different frequencies, it can be shown that the envelope of the standing wave is a carrier of information which is specific to each frequency: the voltage detected along the transmission Line 200 is the sum of the voltages which would be obtained for each elementary signal separately.

In the case of a complex signal, a filter, digital for example and not represented in the figures, makes it possible to isolate the different envelopes corresponding respectively to tE e elementary signals. For each envelope it is thus possible to calculate the spatial delay and/or the frequency of the pair of elementary signals which have created the corresponding standing wave.

Figure 4 represents another embodiment of the transmission unit 2 which, linked to circuit 3. of Figure 3, can be used in the device of the invention illustrated by Figure 2.

The transmission unit 2 may also comprise two parallel transmission lines 210 and 220 terminated at one end by their characteristic impedance Z1 and Z2 respectively, their other end being arranged facing the end of the other line which is terminated by the characteristic impedance.

The first and second inputs A and B of transmission unit 2 are constituted by the open end of the first and second transmission lines 210, 220 respectively.

Each means of coupling 201, 202, ..., 20N may comprise a first and second coupler sampling a part of the signal transmitted by the first and second lines 210 and 220 respectively and a circuit producing the summation of the sampled signals. In a simpler manner each means of coupling.201, 202, ..., 20N may be coupled at one and the same time to the first and second transmission lines.

Summation of the sampled signals on each line at the two points M1, M'1; ...; or MN, M'N situated opposite each other thus occurs. In such a construction the lines 210 and 220 operate in a progressive manner. This embodiment makes it possible to amplify the signals along the lines if there is need whereas in the embodiment of Figure 3 amplification can only be provided at the inputs A and B of line 200.

The reference Mo is here constituted by two points: M'o for line 210 and M"o for line 220, points M'o and M"o being situated opposite each other and such that the elec trical paths AM'o and BM11o are equal.

Figure 5 represents another embodiment of circuits 2 and 3 of Figure 2.

Transmission unit 2 comprises a distributed constant transmission line 230, of the coaxial type for example, whose two ends constitute the two inputs A and B of transmission unit 2 and whose linear inductances are designated by L. The means of coupling for sampling the standing wave are composed of transistors shown in Figure 5 by their sthematic equivalents 201, 202, .., 20N. The input stray capacitance of the transistors appears in the calculation of linear impedance of the line and the input capacitance of each coupling transistor is shown by a single capacitance indicated by C.

Detectors 301, 302, ..., 30N of sub-assembly 3 are each constituted by the placing of a rectifier diode D and a capacitance C' in parallel. A space-time converter 31, for example as in Figure 3, completes the sub-assembly 3, which issues at its two outputs 311 and 312 a signal Sp representing the envelope of the standing wave, and SR a space-time reference signal, respectively.

The device according to the invention may be used as a frequency meter only. In this case it is not necessary to inject the signal of unknown frequency into the two inputs A and B of transmission unit 2: one input only is used, A for example, the other input B being terminated with a short circuit.

In the device according to the invention, the high frequency part 2 is reversible: a high frequency signal injected into the output of one of the coupling means 201, 202, ..., 20N issues, at its two ends A and B of the transmission unit, two signals of equal amplitude, of the same frequency, which have a spatial delay which is independen of the frequency and which may be used, for example, to transmit in a defined direction.

A device has thus been described which makes possible the calculation of the spatial delay of two signals of the same frequency, independently of the frequency of the two signals, this device also making it possible to calculate the frequency of the two signals, independently of the calculation of the spatial delay.

Claims

1. Process for the measurement of the spatial delay between two incident signals of the same frequency, which comprises successively: - a first stage for injection of the two signals at two points of the transmission unit in such a way that in the transmission unit they propagate in opposite direc tons:: - a second stage of determination of a reference dis- tance, relative to one of the signal injection points, for which the electrical paths traversed respectively in the transmission unit by the two signals from their injection point are equal; - a third stage of generation of the envelope of the resultant wave existing in the transmission unit; - a fourth stage of measurement of the gap separating the,reference distance and the position of maximum envelope amplitude closest to the said reference distance, and - a fifth stage of computation of the spatial delay which exists between the two incident signals of the same frequency at the input of the transmission unit and which is equal to twice the calculatedgap.

2. Measurement process as claimed in claim 1, which, after the third stage, comprises a sixth stage for the measurement of the gap separating two successive maxima of the envelope of the resultant wave existing in the transmission means, followed by a seventh stage of calculation of the period of the incident signals by multiplying the gap between two successive maxima by a coefficient 2/c in which c is the speed of light.

3. Measurement process as claimed in claim 1 or 2, which, in the case where each incident signal is composed of the same plurality of elementary signals of different frequencies, comprises a supplementary stage for filtering the envelope of the resultant wave existing in the transmission means in order to generate a plurality of elementary envelopes corresponding respectively to the resultant wave of a pair of elementary signals of the same frequency propagating in opposite directions.

4. Measurement process as claimed in any of claims 1 to 3, wherein the envelope of the resultant wave is generated by sampling the resultant wave at a plurality of N points in the transmission unit, detection of each sample taken, processing of the plurality of N detected samples each corresponding to a sample point situated on one side or the other of the reference by a defined gap from the said reference distance, in order to generate a sampled curve representing the variations of the envelope of the resultant wave as a function of time.

5. Measurement process as claimed in claim 4, wherein, as the transmission unit comprises two transmission circuits in which two incident signals propagate respectively in opposite directions, detection is performed for the plurality of signals corresponding to the sum of the two sampled signals on both of the transmission circuits at a point situated at the same gap and on the same side of the said reference distance.

6. Measurement process as claimed in claim 4 or 5, wherein the detection is quadratic.

7. Measurement device of the spatial delay between a first and a second signal having the same frequency Cf), which cdmprises: - a unit (2) for the transmission, in opposite directions, of the two signals applied to its input; - means (3) of generating the envelope (Sp) of the resultant wave existing in the transmission unit; - means (4) of measuring the gap (so), relative to a reference distance, from the position of maximum amplitude of the envelope (Sp) closest to the said reference distance, and of calculating the spatial delay (S) which exists between the two incident signals at the input of transmission unit (2) and which is equal to twice the cal created gap (so), the reference distance being the distance for; which the electrical paths traversed by the incident signals from their respective injection point (A,B) in transmission unit (2) are equal.

8. Measurement device as claimed in claim 7, which comprises in addition means (5) of calculating the period 1 (f) of the incident signals which are equal, except for 2 the coefficient c' to the gap ( A s) measured between two succes-ive maxima of the envelope (Sp) of the resultant wave existing in the transmission unit (2), c being the speed of light.

9. Measurement device as claimed in claim 7 or 8, which, as the first and second incident signals are composed respectively of the same plurality of (M) elementary.

signals of different frequencies, comprises in addition means of filtering which receive means of generation (3) of the envelope (Sp) of the resultant wave existing in the transmission unit (2) and which issue a plurality of (M) elementary envelopes, each elementary envelope being the envelope of the wave resulting from the propagation in opposite directions of a first and a second elementary signal of the same frequency which compose respectively the first and second incident signals.

10. Measurement device as claimed in claim 7 or 8, wherein the transmission unit (2) is constituted by a transmission line (200, 230) at the ends (A,B) of which the first and second incident signals are respectively applied.

11. Measurement device as claimed in claim 7 or 8, wherein the transmission unit (2) is constituted by a first and second transmission line (210, 220) which are parallel, loaded at their first end by their respective characteristic impedance (Z1, Z2) and fed at their second end (A,B) by the first and second incident signals respectively ,the first end of one transmission line (210, 220) being arranged opposite the second end of the other line (220, 210) so that the first and second incident signals propagate in opposite directions.

12. Measurement device as claimed in claim 10, wherein, as a plurality of N samples of the resultant wave existing in the transmission unit (2) have been respectively taken by a plurality of N means of coupling (201, 202, ..., 20N), the means of generation (3) of the envelope (Sp) of the resultant wave-comprise:: - a plurality of N means of detection (301, 302, ..., 30N) fed respectively by a sample taken by the means of coupling (201, 202, ..., 20N)p and - means of space-time conversion (31) which, from the plurality of N detected samples, each corresponding to one defined position relative to the reference distance, generate a sampled curve (Sp) representing the variations of the amplitude of the detected samples as a function of time, and a reference signal (SR) indicating the position of the sampling points relative to the reference distance as a function of time.

13. Measurement device as claimed in claim 11, wherein a plurality of N means of coupling (201, 202, ..., 20N) each take a sample of the first incident signal on the first transmission line (210) and a sample of the second incident signal on the second transmission line (220) and generate from them respectively the sum, the points at which each means of coupling (201, 202, ..., 20N) takes samples of the first and second incident signals being arranged opposite each other and having the same position relative to the reference distance, and -wherein the means (3) of generating the envelope of the resultant wave comprises: - a plurality of N means of detection (301, 302, ..., 30N) fed respectively by a sample taken by the means of coupling (201, 202, ..., 20N); and - means of space-time conversion (31) which, from the plurality of N detected samples each corresponding to one defined position relative to the reference distance, generate a sampled curve (Sp) representing the variations in amplitude of the detected samples as a function of time and a reference signal (SR) indicating the position of the points for taking samples relative to the reference distance as a function of time.

14. Measurement device as claimed in claim 12 or 13, wherein the means of detection (301, 302, ..., 30N) are quadratic detectors.

15. Measurement device as claimed in clain 12 or 13, wherein the space-time conversion means (31) omprise an N-input commutator fed respectively by the N detected samples which are successively switched to the output of the commutator at the rate of an external control pulse signal and a circuit which, from the control pulse signal issues a signal which represents, for each pulse and thus for each sample of the envelope, the position of the cor-responding sample taken on the transmission unit (2) relative to the reference distance.

16. A process for the measurement of spatial delay substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

17. A measurement device substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

Amendment to the claims have been filed as follows:

1. A process for the measurement of a spatial delay between two incident microwave signals of the same frequency, the delay corresponding to the difference in the paths traversed by two points P1 and P2 of the front of a transmitted wave before reaching a reference plane, said process comprising:: - a first stage for injection of the two signals at two points of a transmission unit in such a way that in the transmission unit they propagate in opposite directions; - a second stage of choice of a reference point of the transmission unit relative to one of the signal injection points, for which the electrical paths traversed respectively in the transmission unit by the two signals from their injection points are equal; - a third stage of determination of the spatially-varying envelope of a resultant wave which comprises samples taken at points spaced relative to one of the signal injection points of the electrical paths traversed respectively in the transmission unit by the two injected signals; - a fourth stage of measurement of the gap separating the reference point and the position of maximum envelope amplitude closest to the said reference point and;; - a fifth stage of computation of the spatial delay which exists between the two incident signals of the same frequency and which is equal to twice the calculated gap.

2. A measurement process as claimed in claim 1, which, after the third stage, comprises a sixth stage for the measurement of the gap separating two successive maxima of the envelope of the resultant wave existing in the transmission means, followed by a seventh stage of calculation of the period of the incident signals by multiplying the gap between two successive maxima by a coefficient 2/c in which c is the speed of light.

3. A measurement process as claimed in claim 1 or claim 2, which, in the case where each incident signal is composed of the same plurality of elementary signals of different frequencies, comprises a supplementary stage for filtering the envelope of the resultant wave existing in the transmission unit in order to generate a plurality of elementary envelopes corresponding respectively to the resultant wave of a pair of elementary signals of the same frequency propagating in opposite directions.

4. A measurement process as claimed in any of claims 1 to 3, wherein the envelope of the resultant wave is determined by sampling the resultant wave at a plurality of H points in the transmission unit, detection of each sample taken, processing of the plurality of N detected samples each corresponding to a sample point situated on one side or the other of the reference by a defined gap from the said reference distance, in order to generate a sampled curve representing the variations of the envelope of the resultant wave as a function of time.

5. A measurement process as claimed in claim 4, wherein, as the transmission unit comprises two transmission circuits in which two incident signals propagate respectively in opposite directions, detection is performed for the plurality of signals corresponding to the sum of the two sampled signals on both of the transmission circuits at a point situated at the same gap and on the same side of the said reference distance.

6. A measurement process as claimed in claim 4 or claim 5, wherein the detection is quadratic.

7. A measurement device for measuring a spatial delay between a first and a second microwave signal having the same frequency (f), this delay corresponding to the difference in the paths traversed by two points P1 and P2 of the front of a transmitted wave before reaching a reference plane, said device comprising:: - a unit for the transmission, in opposite directions, of the two signals which are applied each to a respective one of its inputs; - means for determination of the spatially-varying envelope of a resultant wave which comprises samples taken at points spaced relative to one of the signal injection points of the electrical paths traversed respectively in the transmission unit by the two injected signals;; - means for measuring the gap between a reference point and the position of maximum amplitude of the envelope closest to the said point and of calculating the spatial delay which exists between the two incident signals and which is equal to twice the calculated gap, the reference point being the point at which the electrical paths traversed by the incident signals from their respective injection points in the transmis-- sion unit are equal.

8. A measurement/as ciaimed in claim 7, which comprises in addition means of calculating the period (f) of the incident signals which are equal, except for the coefficient c2, to the gap measured between two successive maxima oi the envelope of the resultant wave existing in the transmission unit, c being the speed of light.

9. A measurement device as claimed in claim 7 or claim 8, which, as the first and second incident signals are composed respectively of the same plurality of (M) elementary signals of different frequencies, comprises in addition means of filtering which receive means of determination of the envelope of the resultant wave existing in the transmission unit and which issue a plurality of (M) elementary envelopes, each elementary envelope being the envelope of the wave resulting from the propagation in opposite directions of a first and a second elementary sig nal of the same frequency which compose respectively the first and second incident signals.

10. A measurement device as claimed in claim 7 or claim 8, wherein the transmission unit is constituted by a transmi ssion line at the ends of which the first ~~~~~~~~~~~~~~~~ and second incident signals are respectively applied.

11. A measurement device as claimed in claim 7 orclaim 8, wherein the transmission unit is constituted by a first and second transmission line which are ~~~~~~~~~~~~~~~~~~~ paraLlel, loaded at their first end by their respective characteristic impedance and fed at their second end by the first and second incident signals respectively ,the first end of one transmission line being arranged opposite the second end of the other line so that the first and second incident signals propagate in opposite directions.

12. A measurement device as claimed in claim 10, wherein, as a plurality of N samples of the resultant wave existing in the transmission unit have been respectively taken by a plurality of N means of coupling the means of generation of the envelope of the resultant wave comprise: - a plurality of N means of detection fed respectively by a sample taken by the means of coupling and - means of space-time conversion which, from the plurality of N detected samples, each corresponding to one defined position relative to the reference distance, generate a sampled curve representing the variations of the amplitude of the detected samples as a function of time, and a reference signal indicating the position of the sampling points relative to the reference distance as a function of time.

13. A measurement device as claimed in claim 11, wherein a plurality of N means of coupling each take a sample of the first incident signal on the first transmission line and a sample of the second incident signal on the second transmission line and generate from them respectively the sum, the points at which each means of coupling takes samples of the first and second incident signals being arranged opposite each other and having the same position relative to the reference distance, and wherein the means of generating the envelope of the resultant wave comprises:: - a plurality of N means of detection fed respectively by a sample taken by the means of coupling and - means of space-time conversion which, from the plurality of N detected samples each corresponding to one defined position relative to the reference distance, generate a sampled curve representing the variations in amplitude of the detected samples as a function of time and a reference signal indicating the position of the points for taking samples relative to the reference distance -as a function of time.

14. A measurement device as claimed in claim 12 or claim 13, wherein the means of detection are quadratic detectors 15. A measurement device as claimed in claim 12 or claim 13, wherein the space-time conv,ersion means comprise an N-input commutator fed respectively by the N detected samples which are successively switched to the output of the commutator at the rate of an external control pulse signal and a circuit which, from the control pulse signal issues a signal which represents, for each pulse and thus for each sampLe of the envelope, the position of the cor-responding sample taken on the transmission unit relative to the reference distance.