RU2846409C1 - Multi-range hydroacoustic signal direction finder - Google Patents

Abstract

FIELD: detecting hydroacoustic signals.

SUBSTANCE: invention relates to means of detecting hydroacoustic signals in a wide frequency range and can be used for underwater vehicles, bottom and buoy hydrophysical stations. To solve the task of expanding the frequency range of a direction finder, having a static fan of spatial channels with a DN of “reverse cardioid” type, each of DN uses two receivers spaced apart by linear distance d_n=λ_n/4, 1 ≤ n ≤ Q corresponding to n-th frequency range, λ_n is average wavelength of n^th frequency range with average frequency ƒ_n. As a result, a static fan of spatial channels is formed, which consists of 2QN beam patterns, where N is the number of receivers, Q is the number of frequency subbands. In the disclosed direction finder, the bearing determining system includes Q generators having the same structure, but each of them is configured to operate in one of the frequency ranges. Also included is a unit of Q switches, closed in initial state, and a system for selecting a frequency range. In this system, a signal is received by a omnidirectional wide-band receiver. Maximum spectral component is picked up, the frequency subband is determined and a signal is sent to open one of the switches.

EFFECT: wider frequency range of the direction-finding hydroacoustic signal sources, broader functional capabilities of the direction-finder while maintaining direction-finding accuracy with a fixed antenna diameter, without shielding the receivers.

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Description

The invention relates to means for detecting hydroacoustic signals in a wide frequency range and can be used for underwater vehicles, bottom and buoy hydrophysical stations.

Systems designed to determine the direction to a signal source are called direction finders. The general principles of constructing hydroacoustic signal direction finders are described in the book [Handbook of Hydroacoustics / edited by A.E. Kolesnikov. L.: Sudostroenie, 1988. Pp. 18-30]. To exclude the omission of short signals, the direction of arrival of which is not known in advance, a static fan of spatial channels (SC) is formed in the direction finder, allowing simultaneous detection of signals in the entire space, i.e. in a 360° sector. In this case, the direction to the signal source is determined by the direction of the axis of the radiation pattern (RP) of the PC, where there is a maximum signal level. The error in determining the direction is approximately half the angular width of the RP at a level of -3 dB [Handbook…].

The antenna of the direction finder, forming a static fan of the DP, is a cylinder, along the generatrix of which N hydroacoustic receivers are located. To form a given DP width, a working sector of 120° is often used, the DP axis (the direction of the maximum) passes along the line connecting the center of the cylinder and the center of the working sector. With a uniform arrangement of receivers, a shift of the working sector by one step Δθ° = 360° / N changes the direction of the DP maximum by an angle of A6. It is easy to see that the number of static DPs (PK) is equal to N.

The formation of a static fan pattern using a cylindrical antenna is described in the patent for a hydroacoustic station for detecting small-sized objects [RU Patent No. 2680673, IPC G01S15/04, published on 04.12.2017], and the author's certificate for a device for omnidirectional reception of communication signals and identification of a hydroacoustic station [USSR Patent No. 1840778, IPC G01S7/52, published on 27.07.2009] presents a diagram for the formation of a static fan pattern,

A common drawback of the presented technical solutions is the significant diameter of the cylindrical receiving antenna. Let us designate the RP width at the level of -3 dB as Δθ ₀₇ . If it is necessary to obtain the value Δθ ₀₇ = 4° at a frequency of 3 kHz, the cylinder diameter with a working sector of 120° should be 7.36 m, and for a frequency of 1 kHz the required cylinder diameter will be 22.1 m.

Since the static fan pattern must cover a sector of up to 360°, it is necessary to shield the rear surfaces of the receivers to eliminate the ambiguity of the bearing to the signal source. This circumstance creates additional problems, especially when forming a pattern with high directivity at low frequencies.

To construct a screenless receiver, a receiver that forms a unidirectional cardioid RP can be used [Smaryshev M.D. Elements of the Theory of Directivity of Hydroacoustic Antennas. St. Petersburg: Publishing House of St. Petersburg Electrotechnical University "LETI", 2003, pp. 56-60]. The RP is formed by two non-directional hydroacoustic receivers, the linear distance between which is equal to a quarter of the wavelength of the carrier frequency of the received signal.

In the method and device for determining the direction to the source of a sound signal by a diver [RU Patent No. 2439602, IPC G01S 7/52, published 27.08.2011], it is proposed to form an "inverse" cardioid radiation pattern. In this case, the formation path consists of a signal delay device for a time equal to a quarter of the period of the carrier frequency of the received signal, a summer, and an amplifier with automatic gain control (AGC). The gain of the amplifier with AGC is inversely proportional to the level of the control signal coming from the output of the summer, and at the output of the amplifier with AGC, a radiation pattern is formed that is "inverse" to the cardioid radiation pattern, the axis of which has the direction along the line connecting the receivers. However, the device proposed in Russian Patent No. 2439602 does not contain a fan pattern generator.

In a compact hydroacoustic signal direction finder [RU Patent No. 2793149, IPC G01S 1/801, published on March 29, 2023], 2N hydroacoustic receivers (HAR) are uniformly distributed around the circumference of the cylinder on a cylindrical antenna with a diameter of D = λ / 4, where λ is the wavelength at the center frequency of the received signal, connected to a 2N-channel spatial channel forming unit configured to form a static fan of 2N spatial channels (SC) in the angular range of 360 °. In each SC, a "reverse" cardioid DP is formed. The device also contains a 2N-channel bearing determination unit, where the SC _n in which the maximum level of the received signal is recorded is determined. The direction θ _n of the DP axis of this SC is taken as the direction to the signal source, and the bearing value is transmitted to external devices using the transmission unit. The main disadvantage of the presented technical solution is the low angular resolution, i.e. the large error in determining the bearing to the target, since the direction to the signal source being taken is determined with an accuracy of no more than half the beamwidth Δθ ₀₇ [Reference…].

The closest in technical and functional characteristics to the proposed device is the “Hydroacoustic signal direction finder that forms a static fan of spatial channels” [RU Patent No. 2810696, IPC G01S 3/80, published 12/28/2023], which is adopted as a prototype.

The direction finder, declared in the Russian Federation patent No. 2810696, with a small diameter of the cylindrical antenna forms a static fan of 2N spatial channels, where N is the number of hydroacoustic receivers in the antenna. The distance between each pair of hydroacoustic receivers forming a RP of the "inverse cardioid" type is D = λ / 4, i.e. the average frequency of the received signal should be ƒ _ср ⁼ c / (4D). As shown in the work [Smaryshev M.D. ... pp. 56-60], a cardioid RP is formed at a distance between the HAPs d = λ / 4, and in the case of the prototype device d = D. If the frequency of the received signal ƒ _с ≠ ƒ _ср , the cardioid RP is distorted. As shown in [Smaryshev M.D.…, pp. 56-60], within the limits of signal frequency variation ƒ _c ≈ _{ƒ cp} ±0.2 ƒ _cp, the RP distortions can be neglected. With a further difference between ƒ _c and ƒ _ср , high-level maxima arise in the direction opposite to the main RP maximum, and the main maximum is strongly distorted to the point of degeneration. In this case, dips and additional maxima arise in directions different from the directions when receiving a signal of frequency ƒ _ср . Thus, with a constant diameter of the cylindrical antenna, the device according to the prototype patent has a very limited working signal reception band, which is a significant drawback limiting the use of such direction finders.

The main objective of the invention is to expand the frequency range of the direction-finding sources of hydroacoustic signals, which, in turn, significantly expands the functional capabilities of the direction finder, maintaining the accuracy of direction finding with an unchanged antenna diameter, without shielding the receivers.

To solve the stated problem, new features have been introduced in a direction finder containing a cylindrical antenna made sound-transparent and consisting of N non-directional hydroacoustic receivers, wherein the phase centers of all the hydroacoustic receivers are uniformly distributed with an angular step of Δ0°=(360/N)° around the circumference, as well as a bearing determination system containing a first formation unit (FU) made with the possibility of forming a static fan of 2N spatial channels (SC) and determining the direction to the signal source, wherein in each of the SCs a directivity pattern (DP) of the "inverse cardioid" type is formed, namely:

the number of GAPs present in a cylindrical antenna is N=2n+1, where n is an integer (n≥1),

the direction finder is additionally equipped with a block of Q (Q is the number of frequency ranges) keys (KL) closed in the initial state and a frequency range selection system (FRS), and the bearing determination system is additionally equipped with Q-1 (Q≥2) BF blocks, identical in structure but differing in the values of the linear distance d between the two GAPs participating in the formation of the DN, wherein each of the BF blocks is designed with the ability to operate in one of the Q frequency ranges;

to form each of the 2QN directivity patterns, 2 GAPs are used, spaced from each other at a linear distance d _n = λ/4, 1≤n≤Q, corresponding to the n-th frequency range, λ _n is the average wavelength of the n-th frequency range with an average frequency ƒ _n ;

the output of each GAP is connected to the corresponding input of each of the Q blocks of the BF, the output of each of the BF blocks is connected to the signal input of the corresponding key of the BKl block, and the Q outputs of the SCD are connected to the control inputs of the corresponding keys of the BKl block.

The required result is obtained if the frequency range selection system (FRS) contains a series-connected non-directional reception unit (NDU) and a control unit for opening the key of the required frequency range (CU), wherein the NDU consists of a non-directional hydroacoustic receiver, the passband of which is made equal to the passband of the GAP, and the CU consists of a series-connected spectral analysis module with the allocation of the maximum spectral component (MSC), a frequency range determination module (FRD) and a control signal transmission module (CSM) for opening the key of the BKl unit of the corresponding frequency range, wherein the NDU is connected to the MSA module, and the CSM module is connected via a bus to the BKl unit.

The main technical result of the invention is the expansion of the frequency range of received hydroacoustic signals emitted by the target object. This result is fundamentally achieved by the fact that the distance between the hydroacoustic signals providing the formation of each cardioid RP, d _n = D _sin (nΔθ/2), where n is the frequency range number (n=1,2,…, Q).

The introduction of new features ensures the expansion of the frequency range of the direction-finding source of hydroacoustic signals with an unchanged diameter of the cylindrical antenna, which expands the functional capabilities of the direction finder.

The essence of the invention is explained in Fig. 1, 2. Fig. 1 shows a generalized functional diagram of the device; Fig. 2a-2g show possible pairs of HAs forming a cardioid RP, and the double line shows the cylinder guide on which the HAs are located. In Fig. 2a, each such pair is receivers adjacent in location on the cylinder generatrix; in Fig. 2b, the corresponding pair is located at an angular distance of 2Δθ, in Fig. 2c - at a distance of 3Δθ, and in Fig. 2g - at a distance of 4Δθ. For clarity, the corresponding pairs of HAs are connected by lines.

The direction finder (Fig. 1) comprises a cylindrical antenna 1, a bearing determination system 2, a Q-channel key block 3 (KL) and a frequency range selection system 4 (FRS). Hydroacoustic receivers GAP ₁ , GAP ₂ , ... GAP _N are located on the guide of the cylindrical antenna 1. The bearing determination system 2 consists of Q independent generating blocks BF _1, BF ₂ , ... BF _Q , each of the blocks B _n is configured to form a static fan of 2N spatial channels (PC) and determine the direction to the signal source, a description of the structure of an individual BF block is given in the prototype patent of the Russian Federation No. 2810696. The key block 3 consists of Q (according to the number of frequency ranges of the direction finder) keys. The frequency range selection system 4 consists of a non-directional reception unit 5 (NDU) and a frequency range selection unit 6 (FSU). The BNP unit consists of a non-directional hydroacoustic receiver, the bandwidth of which is made equal to the bandwidth of the GAP. The BVD unit 6 consists of a series-connected spectral analysis module 7 with the allocation of the maximum spectral component (MSC), a module 8 for determining the frequency range (FRD) and a module 9 for transmitting the control signal (CSS) for opening the key of the BKl unit of the corresponding frequency range, wherein the BNP unit is connected to the MSA module, and the CSS module is connected by a bus to the BKl unit.

The cylindrical antenna 1 is connected by a data array transmission bus from the GAP to the bearing determination system, with the GAPs intended for bearing finding of the first (high-frequency) range connected to the BF ₁ , and those intended for bearing finding of the Q-th (low-frequency) range connected to the BF _Q. The output of each of the BF formation units is connected to the signal input of the key of the corresponding range of the Q-channel key block 3.

The frequency range selection system 4 is connected via a bus to the control inputs of the key block 3. The output of the block 5 BNP is connected to the input of the block 6 BVD, and from its output via the bus a control signal is transmitted to open the corresponding key of the block 3 BKl. The BNP block is a broadband non-directional hydroacoustic receiver. The block 6 BVD includes a typical radio circuit for determining the frequency of the maximum signal level received by the block 5 BNP, as well as a control signal generator for opening the corresponding key of the block 3 BKl.

The claimed device is equipped with known acoustic and radio-electronic devices. Small-sized hydroacoustic receivers included in the cylindrical antenna 1, as well as a non-directional hydroacoustic receiver (BNP block) are mass-produced by domestic and foreign industry [RU Patent No. 2810696]. Electronic units included in the formation and processing circuits are implemented as hardware and software, and the additionally introduced Q-channel key block 3 and frequency range selection block 6, as well as the bearing determination system 2 described in prototype patent No. 2810696, are expediently formed on the basis of computer technology.

The proposed direction finder works as follows.

The acoustic signal from the source is received by the hydroacoustic transducers (HAT) of the cylindrical antenna 1. All HAT are wideband, covering the entire frequency range of the direction finder. Let the direction to the signal source be θ _source . The signal having an average frequency ƒ _cp = ƒ _n , corresponding to the n-th frequency range, is received in the spatial channels of the direction finder, the RPs of which are oriented in the direction of θ _source . Then the acoustic signal from the source, converted in the HAT into an electrical signal, is transmitted via the bus to the Q BF blocks. In this case, the maximum signal will appear at the output of the BF block _n which is designed with the possibility of processing a signal with an average frequency ƒ _{n of} the n-th frequency range of the direction finder.

The BF„ blocks are identical in structure and differ only in the ability to process a signal of the corresponding frequency range. Signal processing in each of the blocks is described in Russian Federation patents Nos. 2793149 and 2810696, as well as in the report [Krantz V.Z., Ostrovsky D.B. Small-sized direction finder of hydroacoustic signals // Proc. All-Russian Conf. "Applied Technologies of Hydroacoustics and Hydrophysics". St. Petersburg, LEMA Publishing House, 2023. Pp. 129-132].

From the outputs of the BF blocks, signals corresponding to the direction to the source θ _source are transmitted via the bus to the signal inputs of the Q-channel block of keys 3 BKl. Note that in the initial state, all keys of block 3 are closed.

Simultaneously with the reception of the acoustic signal from the source, this signal is received by a broadband non-directional hydroacoustic receiver (block 5 BNP). After the acoustic signal is converted into an electrical signal, it is fed to the input of the frequency range selection block 6 (FRS). In this block, the average frequency of the received signal (ƒ _n) and the corresponding (n-th) frequency range are determined. The signal formed in block 6 is transmitted via the bus to the control input of the key Kl _n , which opens and passes the signal containing information about the direction to the source (bearing) θ _source (see Fig. 1).

Thus, the claimed technical effect is achieved, consisting in expanding the frequency range of the direction-finding sources of hydroacoustic signals and, accordingly, increasing the functional capabilities of the direction finder. Note that with a constant diameter of the cylindrical antenna, the average frequency of the high-frequency range of the direction finder ƒ _v will be when forming the corresponding PC and RP, when the pairs of the cardioid RPs of the GAP are at a minimum distance (see Fig. 2a). The average frequency of the low-frequency range of the direction finder ƒ _n will be when the pairs of the cardioid RPs of the GAP are at a maximum distance (see Fig. 2g).

The declared hydroacoustic direction finder can be used for monitoring underwater conditions when installed on small-sized carriers where there is no possibility of placing large-diameter antennas.

Claims (2)

1. A hydroacoustic signal direction finder comprising a cylindrical antenna made sound-transparent and consisting of N non-directional hydroacoustic receivers (HAR), wherein the phase centers of all HARs are uniformly spaced with an angular step of Δθ°=(360/N)° around the circumference, as well as a bearing determination system comprising a first forming unit (BU) configured to form a static fan of 2N spatial channels (SC) and determine the direction to the signal source, wherein a directivity pattern (DP) of the "inverse cardioid" type is formed in each of the SCs, characterized in that the number of HARs available in the cylindrical antenna is N=2n+1, where n is an integer (n≥1), the direction finder additionally includes a block of Q keys (KL) closed in the initial state and a frequency range selection system (FRS), and the bearing determination system additionally includes Q-1(Q≥2) BU blocks identical in structure to the first block BF, but differing in the values of the linear distance d between the two GAPs participating in the formation of the RP, and each of the BF blocks is configured to operate in one of the Q (Q is the total number of frequency ranges) frequency ranges; to form each of the 2QN RPs, 2 GAPs are used, spaced from each other by a linear distance d _n = λ/4, 1≤n≤Q, corresponding to the n-th frequency range, λ _n is the average wavelength of the n-th frequency range with an average frequency ƒ _n ; wherein the output of each GAP is connected to the corresponding input of each of the Q BF blocks, the output of each BF block is connected to the signal input of the corresponding key of the BKl block, and the Q outputs of the SCD are connected to the control inputs of the corresponding keys of the BKl block. 2. The direction finder according to claim 1, characterized in that the frequency range selection system (FRS) comprises a series-connected non-directional reception unit (NDU) and a control unit for opening the key of the required frequency range (CU), wherein the NDU consists of a non-directional hydroacoustic receiver, the passband of which is made equal to the passband of the GAP, the CU consists of a series-connected spectral analysis module with the allocation of the maximum spectral component (MSC), a frequency range determination module (FRD) and a control signal transmission module (CST) for opening the key of the BKl unit of the corresponding frequency range, wherein the NDU is connected to the MSA module, and the CST module is connected via a bus to the BKl unit.