RU2190237C2 - Reception channel of sonar with uniform linear array resolving the ambiguity of determination of direction of signal arrival - Google Patents

Abstract

FIELD: underwater acoustics. SUBSTANCE: the reception channel of a sonar with a uniform linear array is made in the form of the first group of nondirectional hydrophones with an M-channel directivity pattern forming system and an M-channel operating frequency filter, unit of nondirectional hydrophones with the second directivity pattern forming system and the second operating frequency filter, as well as of 2M-channel multiplexers and 2 M-channel integrators, unit of nondirectional hydrophones made in the form of the second group of nondirectional hydrophones identical to the first group of nondirectional hydrophones and installed in parallel with it; the second directivity pattern forming system and the second operating frequency filter that have M channels and are identical to the first ones; M phases of π/2-phase-shifting circuits and a sign character signal separation unit, having M inputs and 2 M outputs, each pair of outputs of the first and second M-channel filters via the π/2-phase-shifting circuit is connected to the respective inputs of the M-channel multiplexer, and the output of each multiplexer via the respective integrator is connected to the input of the sign character signal separation unit. EFFECT: enhanced truth and noise immunity of the reception channel of a sonar with a uniform linear array at determination of the true direction of signal arrival from half-spaces (starboard or port side, front or rear sector of vision) at a full-scale use of the array wave dimension. 4 dwg

Description

 The invention relates to the field of hydroacoustics and can be used in stationary and ship hydroacoustic complexes (SAC), including in the SAC with flexible linear antennas towed behind the carrier ship.

 The operational experience of sonar stations (HAS) of ships with towed linear antennas indicates the urgency of solving the problem of separate spatial filtering of the primary (when noise direction finding) and secondary (when echolocation) acoustic fields of objects located in opposite half-spaces relative to the antenna.

 It should be noted a significant feature of HAS using linear antennas. This class of receiving antennas, which is widely used in sonar systems, does not allow separate spatial filtering of the acoustic fields of objects located on both sides relative to the receiving antenna without special measures. On the indicators of such GAS information is displayed, combined with two half-spaces. Moreover, there is no fundamental possibility in real time to determine the true coordinates of objects.

 Special maneuvers, which are forced to perform ships towing receiving single-row antennas (see patent [1]), only in the simplest situations allow solving this problem. However, the performance of maneuvering is associated not only with time costs, but also with the appearance of extremely undesirable factors that reduce the effectiveness of the GAS.

 Currently, significant efforts are being made to solve the problem of separate spatial filtering (determining the left-right side) of objects.

 So in the patent [1] on “A method of receiving signals with the elimination of ambiguity using a linear acoustic antenna”, an overview of space is considered when maneuvering a medium using a linear antenna that moves along a “deformed” snake-like path, which leads to a change in the position of the generated spatial channel (PC) in which the signal is observed. The deviation angle of this PC determines the direction to the signal source.

Significant disadvantages of the method include the following:
- the solution to the problem is possible in the simplest jamming situations, i.e. with a small number of objects in the area of the CEO;
- when performing special maneuvering (deformation of a rectilinear motion path), the level of hydrodynamic interference on the towed antenna increases, which leads to the loss of contacts on threshold signals;
- additional time is spent on performing special maneuvering, which in certain situations can be an extremely undesirable factor.

 An active method is also used to solve the problem of separating port and port objects. So, the French company Thomson Sintra ASM [2] developed the ship's GAS SLASM, which for solving the problem under consideration includes a towed long receiving antenna and two radiating antennas (on the starboard and port side), which operate at different but close frequencies. A slight difference in the emitted frequencies from the left and right sides allows you to identify the reflected signals and thereby solve the problem of uncertainty on the sides.

The disadvantages of the considered system include the following factors:
- work is provided only in echolocation mode;
- the creation of unidirectional (in one half-space) emitters in the field of low sound frequencies for the problem under consideration is a complex technical problem.

 US patent [3] proposes a technical solution to the problem of eliminating ambiguity (filtering signals into two half-spaces) in the form of a linear antenna of hydrophones, consisting of three parallel rows (triplet hydrophones), separated from the center of the antenna by 1/3 of the wavelength corresponding to the center frequency of the working range. The density of the aggregate of the middle row of the antenna is higher than the total density of the aggregate of the other two rows, which reduces the possibility of rotation of the antenna around the longitudinal axis when towing. Three rows in cross section form an equilateral triangle in the antenna.

 Three identical static fans of directional characteristics (XH) are formed in three rows of hydrophones. In each of the three HNs of the same name, a phase shift (or time delay) is introduced in a special unit to compensate for phase incursion (or delay) due to the difference in the signal path between the end-row receivers and the central (lower) row. Compensation is provided for two alternatives of signal arrival: from the starboard or port side. Then the sum of the three compensated CNs is made for two alternatives of the signal arrival. In this case, correctly compensated CNs (for the true alternative to the signal arrival) are summed up, and for the false alternative, they are subtracted.

 Thus, the arrival side of the signal is determined by its amplitude from two channels of compensation of XI.

 It is possible to take into account the rotation of the antenna around the longitudinal axis; for this, rotation angle sensors are built into the linear antenna. Their readings are taken into account in the development of compensation phase factors.

The disadvantages of the system include:
- complexity of implementation, as the presence of three rows of hydrophones in the system is assumed;
- the complexity of compensating the difference in the signal path for different directions of the static fan XN;
- the possibility of full compensation (with zero spatial transmission coefficient) only for the central frequency of the working range.

 The closest in technical essence to the proposed invention is the receiving path of the GAS with a linear towed antenna according to the US patent [4].

 The invention provides for the presence of a towed antenna in the GAS receiving path, including a group of omnidirectional hydrophones evenly spaced along the entire length of the antenna, as well as a block of omnidirectional hydrophones, consisting of the first and second additional transducers, each of which includes a set of small hydrophones, and their total output considered as the output of one of two additional converters. Small hydrophones forming additional transducers are placed in parallel and symmetrically with respect to the main hydrophones on a limited length of the opposite sides of the inner wall (shell) of the towed antenna.

 On the basis of a group of omnidirectional hydrophones uniformly distributed over the entire length of the antenna, a static fan of directional characteristics is formed using the first M channel system for the formation of directional characteristics (SPS).

 On the basis of two additional converters with the help of the second two-channel SPS, two directional characteristics are formed in the form of a cardioid with their orientation in opposite half-spaces (towards the left and right sides). The first M channel and second two-channel filters of operating frequencies provide filtering of the signals, respectively, at the output of the first and second SPSH. The formation of M spatial channels of the starboard side by multiplying the CN of a static fan by cardioid CN of additional transducers and M channels of the left side by the output of 2M integrators is provided using 2M multipliers.

The disadvantages of the prototype device include:
- insufficient shielding of acoustic fields from the rear half-space by cardioid receivers (Fig. 4d), which, when the signal / noise ratio is greater than the threshold, does not allow for reliable separation of port and starboard objects (Fig. 4a) and requires additional algorithmic procedures, usually leading to unwanted effects;
- low noise immunity of the spatial channels of the left and right sides, because cardioid receivers are located on a small part of the length of the towed antenna formed by the main group of omnidirectional hydrophones.

 The objective of the invention is to provide a GAS receiving path with a linear antenna that provides real-time increase in reliability and noise immunity when determining the true direction of arrival of signals from half-spaces (left or right side, front or rear viewing sector) with full use of the wave size of the antenna.

To solve this problem, in the receiving path of a hydroacoustic station with a linear antenna, which eliminates the ambiguity of determining the direction of arrival of the signal, containing the first group of omnidirectional hydrophones evenly spaced along the length of the linear antenna, the outputs of which are connected through the channels of the first M channel system for generating directivity characteristics with the inputs of the first M channel operating frequency filter, block of omnidirectional hydrophones, the second directional characteristic formation system Ti, the second filter of operating frequencies, 2M multipliers and 2M integrators, new features have been introduced, namely: the block of omnidirectional hydrophones is made in the form of a second group of omnidirectional hydrophones, identical to the first group of omnidirectional hydrophones, evenly spaced along the length of a linear antenna installed parallel to the first group of omnidirectional hydrophones at 1 <0,5λ _in from it where λ _in - the wavelength in water at the upper frequency operating band, the second system for forming directional characteristics and a second filter servant sneeze M channel frequencies are made identical, respectively, first, into the receiving channel sonar M phase shifting introduced at π / 2, and unit circuits for signal separation landmark feature having M inputs and 2M outputs, each pair of outputs 1 and l ',. ... L and L ', M and M' of the first and second M channel filters through a phase shifting circuit on π / 2 are connected to the corresponding inputs 1, .... L, M of the multiplier, and the output of each of M multipliers through the corresponding integrator is connected with the corresponding input of the signal separation unit by sign.

The proposed structure of the receiving path of the sonar station allows you to achieve the following technical results:
- provides a real-time solution with increased reliability of the main task of separating the acoustic fields of objects located in opposite half-spaces relative to the receiving antenna;
- provides the possibility of indicator observation in wider sectors of the review separately left and right sides;
- increased noise immunity of all PCs [from the own noise emission of the antenna towing];
- the efficiency of further signal processing, i.e. the reliability of the indicator presentation of information increases and the information content of the secondary processing increases, including by eliminating false intersections of tracks (the effect due to the summation of the acoustic fields of two half-spaces);
- eliminates (according to the results of theoretical studies) the need for a complex and far from always effective procedure for centering the indicator process in acoustic noise fields close to isotropic.

 This is achieved by the fact that in one cycle of picking up signals from the output of the integrators, two signal arrays are formed, one of which characterizes the signals of the port side, and the second - signals of the port side. In addition, this problem is solved with the help of all antenna receivers.

 The invention is illustrated figure 1-4, where: figure 1 shows the structure of the proposed receiving trust sonar station, eliminating the ambiguity of determining the direction of arrival of the signal.

 Figure 2 shows the XH of two formed symmetrical relative to the PC antenna (left-right side) with different-sign spatial transmission coefficients at the output of the K-th integrator.

 In FIG. 3 are shown in a three-dimensional coordinate system XH of the spatial channels of the new GAS receiving path with a two-row linear antenna.

 In FIG. 4 presents the simulation results - indicator pictures for the receiving path according to the patent - prototype [4] with XH and the new structure of the HAS receiving path in the same interference-signal situations.

The composition of the receiving path of the HAS (Fig. 1) includes a linear receiving antenna 1, consisting of the first 1a and second 1b parallel identical groups of omnidirectional hydrophones uniformly spaced along the length of the antenna. The first and second groups of hydrophones are spaced at a distance of 1 <λ _in / 2, where λ _in is the wavelength in water for the upper frequency of the operating range. The corresponding outputs of the first group of hydrophones are connected to the same inputs of the first CFS 2, and the outputs of the second group of hydrophones are connected to the same inputs of the second CFS 2. Next, a pair of outputs of the same name 1 and 1 ', ..., L and L', .... M and M 'with SFCH 2 and 2' is connected to the corresponding inputs of two M channel filters of operating frequencies 3 and 3 '. The outputs (l ', ... L', ... M ') of the second M channel filter 3' through phase-shifting circuits 4 and the outputs (1, ... L, ... M) of the first M channel filter 3 are connected to the corresponding the inputs 1, ... L, ... M of the multipliers 5, and the output of each of the M multipliers through the corresponding integrator 6 is connected to the corresponding input of the signal separation unit (BRS) by the sign of sign 7. From the BRS block, the signals are separately sent to the indicators of the left and starboard side (in figure 1 indicators are not indicated). As indicators, any indicators or recorders used in sonar stations can be used.

 All elements included in the structure of the proposed GAS tract (figure 1) are known and widely represented in the literature. Omnidirectional hydrophones, linear antennas, and principles of CN formation on the basis of these hydrophones placed uniformly along the same line using SFN (compensator) are described in sufficient detail in the literature [5, 6].

 Structurally, the antenna can be made in a single hose shell, as described in US patent [4].

 The blocks of filters 3, phase-shifting links 4, multipliers 5, integrators 6 are described in [7].

As a BRS unit, which provides the separation of signals from objects located in opposite half-spaces relative to the antenna, a multi-channel analog-to-digital converter (ADC) can be used, which converts the analog output signals of integrators 6 into a digital code, for subsequent processing in COMPUTER. The output bit of the ADC corresponding to the level of the output signal of the integrator (at the time of reference) contains a signed bit that determines the polarity of the specified signal [8]. In this embodiment, when the ADC converts, for example, the signal of the L-drop of the integrator, then in the sign of the digit of the output word of the ADC of the plus sign, the signal is addressed via the L ^L channel of the BRS (Fig. 1), which corresponds to the port side with the direction to object (for example) 65 ^o relative to the normal to the aperture of the towed AR (figure 2). If when converting the signal of the L-th channel of the integrator in the sign of the ADC output word there is a minus sign, the signal is addressed via the L ^P channel of the BRS (Fig. 1), which corresponds to the starboard side with a direction of 115 ^o relative to the indicated normal (Fig. 2). A similar procedure for separating signals by sign is carried out on all M output channels of each cycle of picking up signals from integrators, resulting in two signal arrays (one review cycle) that provide simultaneous monitoring separately in the viewing sectors of the left and right sides (Fig. 4 b ,in).

 So, a feature of the structure of the receiving path of the station under consideration is a change in the sign of the PC transmission coefficient depending on the half-space relative to the two-row linear antenna in which the acoustic field source is located.

где F_pc(ω) - энергетический спектр шумоизлучения объекта в точке приема;
d, N - расстояние между соседними приемниками вдоль антенны и их количество;
θ,α - углы в сферической системе координат, определяющие направление прихода плоской волны в пространстве;
θ_к - угол в горизонтальной плоскости между нормалью к апертуре антенны и направлением оси ПК;
l - расстояние между рядами антенны;
ω_н,ω_в - круговые частоты границ полосовых фильтров.The sign of the transfer coefficient of an arbitrary PC is determined by its XN, the analytical expression of which in the working frequency band has the following form

where F _pc (ω) is the energy spectrum of the noise emission of the object at the receiving point;
d, N is the distance between adjacent receivers along the antenna and their number;
θ, α are the angles in the spherical coordinate system that determine the direction of arrival of the plane wave in space;
θ _to - the angle in the horizontal plane between the normal to the aperture of the antenna and the direction of the axis of the PC;
l is the distance between the rows of the antenna;
ω _n , ω _in - circular frequencies of the borders of bandpass filters.

и меняется (фиг.2) на углах θ = ±π/2 относительно нормали к апертуре антенны, т.е. при нахождении объекта шумоизлучения (или эхосигнала) с левого борта (или в переднем секторе обзора - для стационарных систем) на выходе соответствующего ПК (выход соответствующего интегратора) сигнал будет иметь положительную полярность.An analysis of expression (1) shows that the sign (polarity) of the DC component at the PC output due to the received signal is determined by the angle θ of the factor

and changes (Fig. 2) at angles θ = ± π / 2 relative to the normal to the antenna aperture, i.e. when a noise object (or an echo signal) is found from the port side (or in the front viewing sector for stationary systems), the output of the corresponding PC (output of the corresponding integrator) will have a positive polarity.

 When an object is located in another half-space relative to the antenna, the signal at the output of any PC (in which the object is located) will have a negative polarity.

 Thus, the sign of the output signals of the PC, highlighted by the signal separation unit 7 (Fig. 1), allows for the separation of noise (spatial filtering) of the total information flow of one review cycle (state of M integrators) into two signal arrays of the corresponding half-spaces with reference signals to true bearings (accurate to PC) on objects.

 The receiving path works as follows.

From the hydroacoustic signals received by the first group of omnidirectional hydrophones (1, ... K, .... N) of the antenna 1, M spatial channels of the static CP fan are formed using the first SPS 2 in a certain field of view with subsequent filtering of the signals by the M channel filter 3 in the working frequency band. From the signals received by the second group of omnidirectional hydrophones (1 ', ... K', ..., N ') of antenna 1, M similar spatial channels (with the same orientation of each PC in the horizontal plane) are formed with the help of the second CFS 2. as with the first SPSF) and the subsequent filtering of the output signals from all PCs with a second similar M channel filter, all outputs of which carry out a phase shift by π / 2 of all spectral components. Further, the signals of the corresponding (oriented in the same direction) pairs of PCs (1 and 1 ', ..., L and L', ..... M and M ') are fed to the corresponding M multipliers 5, the output signals of which after integration by link 6 arrive at the BRS unit, which provides signal arrays separately from the port and starboard PCs, the functional description of which is given earlier. After the BRS block, the signals from the left port and separately from the starboard PC are sent to the corresponding indicators. It should be noted that the phase-shifting link 4 in the corresponding arm of the multiplier 5 provides a change in the sign of the signal from the output of the integrator when the source of the primary or secondary acoustic fields changes to the opposite half-space relative to the antenna, i.e. a sign is formed (for any spectral component of the working frequency range, provided that 1 <λ _in / 2), used in the BRS block for spatial filtering of objects. Thus, the receiving path (Fig. 1) forms a conditional plane perpendicular to the orientation of the two-row antenna (ideally, when the two rows of antennas are oriented in the horizontal plane, this plane is perpendicular to the horizontal plane). All signals located in this plane have a spatial transmission coefficient equal to zero. This circumstance explains a certain degree of protection of the receiving path (antenna) from the tower's own noise emission during its rectilinear movement, as well as a certain suppression of the interference field due to the noisy surface.

 As a result of processing the acoustic signal (Fig. 1) at the output of each integrator, the directivity characteristics of the left-handed and right-handed PCs are formed (Fig. 3) with different spatial transmission coefficients, which allows providing a panoramic view (indicator display in the coordinates "PC" - " Time "- for noise direction finding or" PC "-" Distance "- for echolocation) separately of two half-spaces, as well as determination using known algorithms of coordinates and elements of movement of objects.

 The results of mathematical modeling of the receiving paths of noise-detecting stations in the same noise-signal situations for the proposed structure and for the prototype structure with an antenna providing shielding of one of the half-spaces due to the formation of additional cardioid receivers are presented in Fig. 4.

 The indicator picture I of the detector with a cardioid receiver in the coordinates "PC" - "Time" is presented in figure 4.

 Due to the significant values of the spatial transmission coefficients of cardioid CN from the back, not only objects located in one of the half-spaces (tracks 1, 2, 3), but also objects located in the opposite half-space (tracks 4, 5, 6) are observed on the indicator , with the corresponding level of noise emission (figure 4). The operator perceives the indicator picture literally, naturally believing that he is in contact with six objects located in one of the half-spaces, thereby receiving information from the system that is substantially distorted.

 Indicator pictures of the II port sectors of the port starboard survey (in the same coordinates as indicator picture I) using the information stream for the output of the integrators, after separate spatial filtering of objects in accordance with the new structure of the GUS receiving path (Fig. 1) are presented in Fig. .4.

 According to the indicator patterns II, it can be seen that the new structure of the receiving path separates objects opposite to the receiving antenna half-spaces, ensuring the effective operation of the operator, as well as the issuance of reliable information on the coordinates and elements of the movement of objects.

 Thus, the proposed structure of the GAS receiving path provides with high reliability the determination in the mode of noise direction finding and echolocation the unambiguous direction to the objects.

Sources of information
1. French patent 2727765 from 12/06/1994.

 2. SC Central Research Institute. Acad. A.Ts. Krylova. St. Petersburg Digest, 1994, issue 9, p. 68.

 3. US patent 5058082 from 10.15.1991.

 4. US patent 5220537 from 07.15.1993.

 5. Sverdlin G. M. Hydroacoustic transducers and antennas. Shipbuilding, Leningrad, 1988, p. 88-145.

 6. Tyulin V.P. Theory of acoustic direction finding. VMA, Leningrad, 1954, p. 124-148.

 7. Zaraysky V.A., Tyurin A.M. The theory of sonar, VMA, Leningrad, 1975, p. 283-287, 390-402.

 8. Kuo B. Theory and design of digital control systems. Moscow, Mechanical Engineering, 1986, p.20-29.

Claims (1)

The receiving path of a sonar station with a linear antenna, which eliminates the ambiguity in determining the direction of arrival of the signal, containing the first group of omnidirectional hydrophones evenly spaced along the length of the linear antenna, the outputs of which are connected to the inputs of the first M-channel working filter through the corresponding channels of the first M-channel system for generating directivity characteristics frequencies, a block of omnidirectional hydrophones, a second system for generating directivity characteristics, a second filter of operating frequencies, M multipliers and integrators, characterized in that the block of omnidirectional hydrophones is designed as a second group of omnidirectional hydrophones identical to the first group of omnidirectional hydrophones set evenly along the length of the linear antenna, parallel to the first group of omnidirectional hydrophones at a distance of 1 <0,5λ _B of it where λ _B is the wavelength in water at the upper frequency of the operating range, the second system for generating directivity characteristics and the second filter for operating frequencies are M-channel identical to the first, respectively but, at the same time, the outputs of the omnidirectional hydrophones of the second group are connected to the inputs of the second directional characteristics forming system of the same name, the outputs of the second directional forming system of the same name are connected to the corresponding inputs of the second M-channel operating frequency filter, M phase-shifting by π / 2 are introduced into the receiving path of the hydroacoustic station circuits and a signal separation unit for signs that has M inputs and 2M outputs, with each pair of outputs 1 and 1 ',. . . L and L ',. . . M and M 'of the first and second M-channel filters of working frequencies through a phase-shifting circuit on π / 2 is connected to the corresponding inputs 1,. . . L,. . . M multipliers, and the output of each of the M multipliers through the corresponding integrator is connected to the corresponding input of the signal separation unit by sign.

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