Amplitude goniometer and associated platform TECHNICAL FIELD OF THE INVENTION The present invention relates to an amplitude goniometer and to a platform comprising such an amplitude goniometer. TECHNOLOGICAL BACKGROUND In the field of radar detectors, instantaneous broadband receivers are commonly used because of a very high frequency range to be monitored and the uncertainty about the frequency of the incident signal at a given instant. These radar detectors are also commonly instantaneous goniometers capable of delivering the direction of arrival of an incident radar signal even limited to a single, very brief pulse. The principles of instantaneous direction finding are always based on the use of a set of P antennas, a priori identical, P being at least equal to 2, capable of simultaneously delivering a set of electrical signals, globally carrying the direction of arrival of the incident radio signal. In general, each antenna is followed by a reception chain capable of amplifying and filtering the signal that it supplies to it, the P signals delivered by the P reception chains allowing the estimation of the direction of arrival. It is necessary to distinguish the two cases of goniometer conventionally used: amplitude goniometers and interferometers. All of these goniometers generally use identical antennas of appropriate directivity. The antennas of an amplitude goniometer are angularly pointed offset with respect to each other in the plane of measurement of the angle of arrival of an incident signal, so that their directivity makes them deliver a set of signals whose powers are representative of this angle of arrival. The antennas of an interferometer are angularly pointed in the same direction while being spatially offset with respect to each other in the plane of measurement of the angle of arrival of an incident signal, so that they deliver a set of signals whose relative phases are representative of this angle of arrival. The spectral size of the frequency bands of interest requires having a frequency resolving power, which is very generally done by spectral analysis, and taking into account the available components, made more particularly by digital spectral analysis based on the use of Discrete Fourier transforms (DFT) performed by fast Fourier transforms (FFT, Fast Fourier Transform). So a chain of reception, which is the analog part, is generally followed by a digital reception module comprising an analog-to-digital conversion module, using a sample-and-hold and an analog-to-digital converter working with a sampling frequency f e , itself even followed by a digital signal processing module achieving the desired DFT. Taking into account the very high instantaneous band, typically of the order of at least 16 GHz, there are no reasonably usable analog-to-digital conversion components today capable of respecting Shannon's theorem. In addition, compliance with it would result in digital data flows, typically of the order of 40 Gbit / s, the routing of which by bus poses serious feasibility problems and is not absolutely compatible with the processing capacities of FPGAs. (Field Gâte Programmable Arraÿ) used to create digital signal processing modules. A known solution is to digitize the signal with a sampling frequency that does not comply with Shannon's theorem, so the sampling half-frequency g is less than the frequency band of interest, this is then referred to as sub-sampling. The consequence is the non-respect of the spectral integrity and that the measured frequency, between 0 and the half sampling frequency is ambiguous which imposes the use of several sampling frequencies f e ndifferent and not multiple between them. It will be noted in all rigor that, to respect spectral integrity, Shannon's theorem is a necessary condition but not sufficient. Indeed, respect for spectral integrity is due to the placement of the frequency band of interest in a single Nyquist zone; remember that a sampling frequency f e defines the Nyquist zones as the frequency bands [if, a + Df [. Document WO 2010/069683 A1 discloses sampling the signal with N slightly different and non-multiple frequencies between them, measuring an ambiguous frequency for each sampling frequency, and extracting an unambiguous frequency from of these N ambiguous frequencies. Direct application to a goniometer with P antennas therefore leads to having at the output of each of the P reception chains following each of the P antennas, N digital reception modules in parallel, each digital reception module being composed of a analog-to-digital conversion, working with one of the N different sampling frequencies dedicated to it, and a digital signal processing. Finally, said goniometer with P antennas has PN digital reception modules. This number PN of digital reception modules can quickly become prohibitive for applications for reasons of cost, but also of volume, mass, consumption, heat dissipation and reliability. It is therefore desirable to minimize this number of digital reception modules. Document WO 2004/097450 solves this problem by using a single digital reception module at the output of the reception chain, each digital reception module having a different sampling frequency, and by not using the signal of the channel for which the frequency of the signal is equal to or very close to the half sample rate or one of its multiples. In this case, the goniometer which has P antennas only uses P - 1, which degrades performance. SUMMARY OF THE INVENTION There is therefore a need for a goniometer making it possible to minimize the quantity of equipment with given measurement precision and robustness, the quantity of equipment directly affecting the aspects of cost, volume, mass, consumption, heat dissipation and reliability. Starting from this need, the applicant has proposed to find a solution to substantially reduce the number of digital reception modules. In the case of an interferometer, the technical problem becomes that of distributing the N sampling frequencies over the P reception chains, taking into account the first and second elements which will follow. In the case of an amplitude goniometer, the technical problem becomes that of a distribution of the N sampling frequencies on the Q adjacent reception chains, Q being at most equal to P, taking into account the first, second, third and fourth elements which will follow. The first element to take into account is that a signal of frequency / multiple of the sampling half-frequency, / = k with k non-zero natural integer, cannot be characterized either in amplitude or in phase. Indeed, a sinusoidal signal of frequency /, sampled at the frequency f e has the expression then: s (n) = A cos (nkn + f) = A [cos (nkn) cos ( N = 3. The analog-to-digital conversion modules of the reception channel indexed 0 are associated respectively with the sampling frequency indexed 0, f e 0 , and with the sampling frequency indexed 1, f e l . The analog-to-digital conversion modules of the indexed reception channel 1 are associated respectively with the indexed sampling frequency 1, / el , and with the indexed sampling frequency 2, f e 2 . The analog-to-digital conversion modules of the indexed reception channel 2 are associated respectively with the indexed sampling frequency 2, f e 2 , and with the indexed sampling frequency 0, f e 3. The analog-to-digital conversion modules of the indexed reception channel 3 are associated respectively with the indexed sampling frequency 0, f e 0 , and with the indexed sampling frequency 1, / el . This being the case, the analog-to-digital conversion modules of the reception channel indexed 3 could also have been associated respectively with the sampling frequency indexed 1, / el , and with the sampling frequency indexed 2, f e 2 , or at the sampling frequency indexed 2, / e 2 , and at the sampling frequency indexed 0, fe, 0 FIG. 5 illustrates a case where the number of reception channels P is less than the number of sampling frequencies N, in this case P = 3 0 , and the sampling frequency indexed 1, / el , and G t comprising the sampling frequency indexed 2 , / e 2 , and the sampling frequency indexed 3, f e 3 . The analog-to-digital conversion modules of the reception channel indexed 0 are associated respectively with the sampling frequency indexed 0, f e> 0 , and with the sampling frequency indexed 1, f e l . The analog-to-digital conversion modules of the indexed reception channel 1 are associated respectively with the indexed sampling frequency 2, f e 2 , and with the indexed sampling frequency 3, f e 3 . The analog-to-digital conversion modules of the reception channel indexed 2 are associated respectively with the sampling frequency indexed 0, f e> 0 , and with the sampling frequency indexed 1, f e l. The analog-to-digital conversion modules of the indexed reception channel 3 are associated respectively with the indexed sampling frequency 2, f e 2 , and with the indexed sampling frequency 3, f e 3 . The analog-to-digital conversion modules of the indexed reception channel 4 are associated respectively with the indexed sampling frequency 0, f e 0 , and with the indexed sampling frequency 1, f 6 1 . The analog-to-digital conversion modules of the indexed reception channel 5 are associated respectively with the indexed sampling frequency 2, f e 2 , and with the indexed sampling frequency 3, f e 3 . Fig. 7 illustrates a case where the instantaneous angular coverage is 360 ° with N = 4, P = 5 and Q = 2. N = 4 e. Q = 2 cause / = 2 and consequently that P is not a multiple of J, and Q is less than P. There are two groups of sampling frequencies: G 0 comprising the sampling frequency indexed 0, f e 0 , and the sampling frequency indexed 1, f 6 1 , and comprising the sampling frequency indexed 2, f e 2 , and the sampling frequency indexed 3, f e 3 . The analog-to-digital conversion modules of the reception channel indexed 0 are associated respectively with the sampling frequency indexed 0, f e 0 , and with the sampling frequency indexed 1, f B l . The analog-to-digital conversion modules of the indexed reception channel 1 are associated respectively with the indexed sampling frequency 2, f e 2 , and with the indexed sampling frequency 3, f e 3 . The analog-to-digital conversion modules of the reception channel indexed 2 are associated respectively with the sampling frequency indexed 0, f e 0 , and with the sampling frequency indexed 1, f 6 1. The analog-to-digital conversion modules of the indexed reception channel 3 are associated respectively with the indexed sampling frequency 2, f e 2 , and with the indexed sampling frequency 3, f e 3 . The reception channel indexed 4 has four analog-to-digital conversion modules: two first associated respectively with the sampling frequency indexed 0, f e 0 , and with the sampling frequency indexed 1, f 6 1 , and two seconds in complementary facts, associated respectively with the sampling frequency indexed 2, f e 2 , and with the sampling frequency indexed 3, f e 3 . FIG. 8 illustrates a case where the instantaneous angular coverage is 360 ° with N = 3, P = 6 e. Q = 2. N = 3 rd. Q = 2 cause / = 2 and consequently that P is a multiple of J. There are two groups of sampling frequencies: G 0 comprising the sampling frequency indexed 0, f e 0 , and the sampling frequency indexed 1, f 6 1 , and G t comprising the sampling frequency indexed 2 , f e 2 , and any sampling frequency different from that indexed 2, f e 2 . For the figure, the chosen sampling frequency is that indexed 0, / e 0 , but it could have been that indexed 1, f e 1 . It should be noted that this possibility of choice is valid at the level of each reception channel using G t . The analog-to-digital conversion modules of the reception channel indexed 0 are associated respectively with the sampling frequency indexed 0, f e 0 , and with the sampling frequency indexed 1, f B l . The analog-to-digital conversion modules of the indexed reception channel 1 are associated respectively with the indexed sampling frequency 2, f e 2 , and with the indexed sampling frequency 0, f e 0 . The analog-to-digital conversion modules of the reception channel indexed 2 are associated respectively with the sampling frequency indexed 0, f e 0 , and with the sampling frequency indexed 1, f 61. The analog-to-digital conversion modules of the indexed reception channel 3 are associated respectively with the indexed sampling frequency 2, f e 2 , and with the indexed sampling frequency 0, f e 0 . The analog-to-digital conversion modules of the indexed reception channel 4 are associated respectively with the indexed sampling frequency 0, f e 0 , and with the indexed sampling frequency 1, f 61 . The analog-to-digital conversion modules of the indexed reception channel 5 are associated respectively with the indexed sampling frequency 2, f e 2 , and with the indexed sampling frequency 0, f e 0 . It should be noted that, in the case of an amplitude goniometer, the second element mentioned in the Summary part of the invention is not taken into account. As explained in this part, the amplitude measurement error, due to the signal filtering conditions different from the DFTs performed by the digital signal processing modules (26) when the sampling frequencies are different, is less critical than the phase measurement error for an interferometer. This error is furthermore minimized by the signal weighting generally used which widens the passband of the DFT filter. The residual error can be corrected if necessary by knowing precisely the frequency of the signal, which is always measured in a radar detector. Finally, the invention has been developed for 1 D goniometers (one dimension), that is to say measuring a single angle, the angle in the plane where the antennas are arranged. It should be noted that the generalization to 2D goniometers (two dimensions), that is to say measuring two angles, the angles situated in two non-parallel planes, is done by following the same basic principles. CLAIMS 1.- Amplitude goniometer (10) comprising P reception channels (V 0 , V P-i ), P being an integer greater than or equal to 2, each reception channel (V 0 , V P _i) being identified by a index p corresponding to a given angular order, the index p being an integer between 0 and P - 1, each reception channel (V 0 , V P-i ) comprising an antenna (A 0 , A P _i) coupled to a chain reception (CR 0 , CR P-i ), each reception chain (CR 0 , CR P-i) being followed by at least two digital reception modules (20) each comprising an analog-to-digital conversion module (22), each analog-to-digital conversion module (22) being associated with a respective sampling frequency, each frequency sampling rate not meeting Shannon's criterion and not being a multiple of one of the other sampling frequencies, N being the number of sampling frequencies associated with the analog-to-digital conversion modules (22) belonging to the P reception channels (V 0, ..., V P-1), N being greater than or equal to 2, each sampling frequency being referenced by an index n, the index n being between 0 and N - 1, the goniometry estimator d 'amplitude working from the amplitudes of the signals coming from at least Q adjacent reception channels among the P reception channels (V 0 , ..., V P _i), Q being at most equal to P, the frequencies of sampling being associated with the analog-to-digital conversion modules (22) of these adjacent Q reception channels (V 0 , ..., V P-i ). 2.- Amplitude goniometer according to claim 1, wherein the N sampling frequencies are divided into] groups of sampling frequencies (G 0 , ..., G ; -1 ), each group comprising at least 2 different sampling frequencies, with J being minimal and at most equal to Q. 3.- Amplitude goniometer according to claim 2, wherein the analog-to-digital conversion modules of a receiving channel of index p are associated with the group of sampling frequencies G p.mo d) , for p ranging from 0 to P - 1. 4 - Amplitude goniometer according to claim 3, wherein the angular coverage is less than 360 °. 5.- Amplitude goniometer according to claim 3, wherein the angular coverage is equal to 360 ° and P is greater than or equal to 3. 6. An amplitude goniometer according to claim 5, wherein P is a multiple of J or is equal to Q. 7 - Amplitude goniometer according to claim 5, in which P is neither a multiple of J nor equal to Q, and in which the sampling frequencies of the groups G R to Gj_ t are respectively associated with moduli of analog-to-digital conversion of complementary digital reception modules, these complementary digital reception modules being assigned in any way to all of the two reception channels V 0 and V P-i , and R being the remainder of the Euclidean division of P by J . 8.- Amplitude goniometer according to any one of claims 1 to 7, wherein the minimum number of adjacent reception channels (V 0 , V P _i) required by the estimate of the direction of arrival is equal to 2. 9. An amplitude goniometer according to any one of claims 1 to 8, comprising a computer (28) suitable for processing the signals originating from the digital reception module (20). 10.- Amplitude goniometer according to any one of claims 1 to 9, wherein each analog-to-digital conversion system (22) is connected to a digital signal processing module (26) suitable for performing a spectral analysis of the signals. sampled signals. 1 1 .- Amplitude goniometer according to claim 10, wherein the spectral analysis is carried out by discrete Fourier transform associated with a weighting of the signals sampled upstream. 12.- Platform comprising an amplitude goniometer according to any one of claims 1 to 1 1.