RU2196362C2 - Method for determination of direction to the source of hydroacoustic signal (modifications) - Google Patents

Abstract

FIELD: underwater acoustics associated with reception of wide-band signals, applicable in hydrophoning, sonar direction finding, detection of hydroacoustic signals, classifying, underwater communication, for underwater geophysical operations. SUBSTANCE: two modifications of the method are claimed. According to the first modification of the method, which includes the reception of signal from the direction of the main maximum of the directional pattern of the multiwire equidistant antenna, the signals are received within frequency band

where c - sound velocity, d - distance between the wires, θ-current angle, θ₀-compensation angle. Within this frequency band one more or several maxima symmetrically positioned relative to the main additional maximum are formed in the directional pattern. The reception frequency is changed up to variation of the angular distances between the main and each of the additional maxima by an angle not less than the angular width of the additional maximum in a level of 3 dB. If the signal is received, the direction of signal input is determined as the direction of the additional maximum. For defining more exactly the direction in the presence of two additional maxima at the varied frequency of reception the directional pattern is turned until one of the additional maxima coincides with the initial one. At fixing of the signal this direction is determined as the direction of signal input from the source, and in its absence - as the direction of the other additional maximum at the initial frequency of reception. According to the second modification of the method, reception is accomplished simultaneously at two different frequencies f_a, f_b, in this case each of frequencies f_a, f_b satisfies condition (1). If the signal is received at both frequencies, the direction of signal input is determined as the direction of the main maximum, if at one of the frequencies - as the direction of the additional maximum at the given first frequency. For defining more exactly the direction in the presence of two additional maxima the directional pattern is turned at the second frequency until one of the additional maxima coincides with the direction of the additional maximum at the first frequency, where the signal is received. At the reception of the signal at the second frequency this direction is determined as the direction of signal input from the source, and in the absence - as the direction of the other additional maximum at the first frequency. EFFECT: expanded frequency band in the range of which the direction to the signal source is determined unambiguously at similar wave dimensions between the antenna wires, enhanced accuracy of direction finding, reduced number of active antenna wires, quantity of channels, cost at the same wave dimension of the antenna. 2 cl, 4 dwg

Description

 The invention relates to the field of hydroacoustics associated with the reception of broadband signals, and can be used for noise direction finding, sonar, detection of hydroacoustic signals, classification, for sonar communication, for underwater geophysical operations.

 In modern hydroacoustics, the reception of signals is carried out by a fan of radiation patterns (MD) or a scanning radiation pattern, while the direction to the signal source is determined by the direction of the maximum of the pattern. The spectral composition of signals emitted by various sources in sonar extends from units of Hz to tens of kHz [1]. For detection and direction finding it is of interest to use the entire spectrum of the signal source. At the same time, there are conditions that limit the range of signals received by a single antenna, and do not make it possible to unambiguously determine the direction to the source of the received signal.

 Methods of receiving signals used in sonar are reflected in the book [2]. Determining the direction of the signal source is one of the main elements of the reception. In this case, the bearing information should clearly correspond to the true direction.

где λ - длина волны принимаемого сигнала, θ₀ - угол компенсации.From the literature on antenna technology [3] it is known that in the case of receiving signals of an equidistant discrete antenna consisting of N elements, the distance d between the phase centers of two adjacent elements must satisfy the relation

where λ is the wavelength of the received signal, θ ₀ is the compensation angle.

Failure to fulfill condition (1) leads to the appearance in the MD of maxima equal to the main one, which leads to ambiguity in determining the direction to the signal source. Therefore, the range of received signals is limited by the frequency f≤f ₀ = cd / 2 (c is the speed of sound). Below the frequency f ₀ , additional maxima equal to the main one do not appear in the DN. The appearance of such additional maxima leads to the ambiguity of the bearing on the target. Thus, the range of received signals in order to unambiguously determine the bearing is limited from above by the frequency f ₀ , which is explained by the general property of equidistant antennas.

A known method for determining the direction to the source of the hydroacoustic signal, comprising receiving a signal from the direction of the main maximum in the frequency range f <f ₀ . This method, widely described in the literature, in particular, in the book [4], is the closest to the proposed, it is advisable to take as a prototype.

The disadvantages of this method are:
- limiting the spectrum of received signals to a frequency above which additional maximums are formed that can give false bearings to the target;
- the inability for this reason to work with a broadband signal above the cutoff frequency from expression (1), which is necessary for various noise signal situations;
- the need for a special high-frequency antenna if the range of signals from the source is higher than the boundary.

Note that when choosing f ₀ as the upper frequency of the operating range, the prototype method becomes less effective in the low-frequency range, since the wave size of the antenna decreases, which leads to beam expansion, reduces the concentration coefficient, and the mutual influence between the elements increases.

 The objective of the proposed method is to expand the frequency range by eliminating the ambiguity of the bearing in the direction of frequencies at which one additional maximum equal to the main one or two additional maximums symmetrically located relative to the main maximum are formed in the radiation pattern of the receiving antenna.

 This problem can be solved by two variants of the method, differing in the sequence of operations, but connected by a common inventive concept.

где с - скорость звука, d - расстояние между элементами, θ - текущий угол, θ₀ - угол компенсации, в котором в диаграмме направленности образуется один дополнительный максимум или два дополнительных максимума, расположенных симметрично относительно главного максимума; изменяют частоту приема таким образом, чтобы изменились угловые расстояния между главным максимумом и каждым дополнительным максимумом на угол, равный угловой ширине дополнительного максимума на уровне - 3 дБ. Если сигнал после изменения частоты принят, то направление прихода сигнала определяют как направление главного максимума диаграммы направленности. Если сигнал после изменения частоты не принят, то направление его прихода соответствует положению оси одного из дополнительных максимумов на первоначальной частоте приема. Для уточнения направления при наличии двух дополнительных максимумов на измененной частоте приема поворачивают диаграмму направленности до совпадения одного из дополнительных максимумов с его первоначальным направлением. При фиксации сигнала это направление определяют как направление прихода сигнала от источника, а отсутствие сигнала - как направление другого дополнительного максимума на первоначальной частоте приема.According to the first embodiment, in a method including receiving a signal from the direction of the main maximum of the radiation pattern of a multi-element equidistant antenna, new features are introduced, namely:
receiving signals in the frequency range

where c is the speed of sound, d is the distance between the elements, θ is the current angle, θ ₀ is the compensation angle at which one additional maximum or two additional maximums are formed in the radiation pattern, located symmetrically relative to the main maximum; change the reception frequency so that the angular distances between the main maximum and each additional maximum change by an angle equal to the angular width of the additional maximum at the level of - 3 dB. If the signal after changing the frequency is received, then the direction of arrival of the signal is determined as the direction of the main maximum of the radiation pattern. If the signal after changing the frequency is not received, then the direction of its arrival corresponds to the position of the axis of one of the additional maxima at the initial reception frequency. To clarify the direction in the presence of two additional maxima at the changed reception frequency, rotate the radiation pattern until one of the additional maxima coincides with its original direction. When the signal is fixed, this direction is defined as the direction of arrival of the signal from the source, and the absence of the signal is defined as the direction of another additional maximum at the initial reception frequency.

где с - скорость звука, d - расстояние между элементами, θ - текущий угол, θ₀ - угол компенсации; в котором в диаграмме направленности образуется один дополнительный максимум или два дополнительных максимума, расположенных симметрично относительно главного максимума, причем на частоте f_b угловое расстояние между главным максимумом и каждым из дополнительных максимумов отличается от аналогичного расстояния на частоте f_a на угол, не меньший угловой ширины дополнительного максимума. Если сигнал принят на обеих частотах, направление прихода сигнала определяют как направление главного максимума, если на одной из частот - как направление дополнительного максимума на данной первой частоте, для уточнения направления при наличии двух дополнительных максимумов поворачивают ДН на второй частоте до совпадения одного из дополнительных максимумов с направлением дополнительного максимума на первой частоте, где сигнал принят. При приеме сигнала на второй частоте это направление определяют как направление прихода сигнала от источника, а при отсутствии - как направление другого дополнительного максимума на первой частоте.According to the second embodiment, in the method including receiving a signal from the direction of the main maximum of the radiation pattern of a multi-element equidistant antenna, the following new features are introduced:
reception is performed simultaneously at two different frequencies f _a , f _b , while each of the frequencies f _a , f _b satisfies the condition

where c is the speed of sound, d is the distance between the elements, θ is the current angle, θ ₀ is the compensation angle; in which one additional maximum or two additional maximums are formed symmetrically relative to the main maximum in the radiation pattern, and at a frequency f _{b the} angular distance between the main maximum and each of the additional maxima differs from the same distance at a frequency f _a by an angle not less than the angular width additional maximum. If the signal is received at both frequencies, the direction of arrival of the signal is determined as the direction of the main maximum, if at one of the frequencies - as the direction of the additional maximum at this first frequency, to clarify the direction in the presence of two additional maxima, turn the beam at the second frequency until one of the additional maxima coincides with the direction of the additional maximum at the first frequency, where the signal is received. When receiving a signal at a second frequency, this direction is defined as the direction of arrival of the signal from the source, and in the absence, as the direction of another additional maximum at the first frequency.

 The first variant of the proposed method is characterized by a sequence of actions: initial fixing the fact of receiving a signal from the source, changing the receiving frequency, turning the beam to clarify the direction in the presence of two additional maxima located symmetrically on both sides of the main maximum. In the second embodiment, reception is carried out simultaneously at two frequencies, and then, to clarify the direction, the beam is rotated. Thus, in the second embodiment of the proposed method, determining the direction to the signal source is faster, but in this embodiment, the organization of two reception channels is required.

Technical results from the use of the proposed method options are:
- expansion of the frequency band by two or more times (towards higher frequencies), in the range of which the direction to the signal source is uniquely determined for the same wave dimensions between the antenna elements;
- the ability to sharpen the radiation pattern and increase the direction finding accuracy when working at higher frequencies;
- an increase of 2-3 times the sector of active review, two (three) rays are simultaneously formed;
- reduction in the number of active elements of the antenna, the number of channels, cost with the same total wave size of the antenna.

 Consider the physical justification for achieving these technical results.

Условие достижения максимума (3), равного главному максимуму:
πd(sinθ-sinθ₀)/λ = nπ, n=0, ±1, ±2, ... (4)
n=0 - в случае главного максимума ДН.The radiation pattern of the equidistant antenna array is written as:

The condition for reaching the maximum (3) equal to the main maximum:
πd (sinθ-sinθ ₀ ) / λ = nπ, n = 0, ± 1, ± 2, ... (4)
n = 0 - in the case of the main maximum of the pattern.

Выражение (6) определяет верхнюю граничную частоту f₀ однолепестковой ДН. Если частота диапазона f<f₀, имеется единственный максимум ДН (главный); если f>f₀, появляются дополнительные максимумы, их положение находится при решении уравнения (6) при заданных d, f≥f₀, θ:
θ_1,2 = arcsin(±c/(fd)+sinθ₀) (7)
Найдем верхнюю граничную частоту f_в такую, что при f>f_в с одной стороны главного максимума (или симметрично с двух сторон) появляются два дополнительных максимума. Такая ситуация имеет место при n=±2, тогда

Сущность изобретения поясняется фиг. 1, 2, 3, 4. На фиг.1 приведена обобщенная структурная схема, реализующая первый вариант способа, на фиг.2 - структурная схема, реализующая второй вариант способа. На фиг.3 - пояснение способа при наличии в ДН одного дополнительного максимума, на фиг.4 - при двух дополнительных максимумах.From (4) it follows that the first additional maxima occur at n = ± 1,
or
d / λ = ± 1 / (sinθ-sinθ ₀ ), (5)
and the frequencies at which these maxima appear:

Expression (6) defines the upper cutoff frequency f _{0 of a} single-leaf pattern. If the frequency of the range f <f ₀ , there is a single maximum of the NAM (main); if f> f ₀ , additional maxima appear, their position is found when solving equation (6) for given d, f≥f ₀ , θ:
θ _1,2 = arcsin (± c / (fd) + sinθ ₀ ) (7)
An upper limiting frequency f _in such that, for f> f _in the one side of the main peak (or symmetrically from both sides) there are two additional maxima. Such a situation occurs for n = ± 2, then

The invention is illustrated in FIG. 1, 2, 3, 4. Figure 1 shows a generalized structural diagram that implements the first variant of the method, figure 2 is a structural diagram that implements the second variant of the method. In Fig.3 - an explanation of the method in the presence in the NAM of one additional maximum, in Fig.4 - with two additional maxima.

The device (figure 1), designed to implement the first variant of the proposed method, contains a series-connected multi-element antenna 1, a multi-channel broadband amplifier 2, a delay line 3, a controlled narrow-band filter 4, as well as a recorder (display, recorder) 5 and switch 6. Device (figure 2) - for the second option, in addition to blocks 1, 2, 3, 6, identical with the blocks of figure 1, contains controllable filters 7 and 8 at frequencies f _a and f _b , respectively, as well as a two-channel recorder 9.

Antenna 1 is intended for beamforming, converting acoustic energy into electrical energy. Multichannel amplifier 2 amplifies the electrical signal, while limiting the passband frequency f _in . Delay line 3 is designed to turn the beam and is controlled by external signals. Managed narrow-band filters 4, 7, 8 extract from the common band of the received broadband signal a signal of the required frequency f _a (f _1,2 ) or f _b . The switch 6 in the detection mode directly connects the delay line to the registrar, in the direction clarification mode, after detecting the signal from the target in a wide band, the switch is switched to the position when the signal passes through the narrow-band filter 4 or filters 7, 8, after which it goes to registrar. Registrars 5, 9 display the received information and enable the operator to make decisions. The recorder displays the coordinates of the target, including angular, spectra of received signals, as well as other information.

 For greater clarity, the demonstration of the principle of action structural diagrams are presented in the form of analog devices. Modern methods make it possible to memorize the necessary frequencies, directions in which additional maxima are formed at these frequencies, and to rotate the beam at a given angle without operator assistance. In the presented variants of the possible implementation of the devices, the controls are omitted, the presence of such blocks complicates the circuit, without further illustrating the proposed method. The antenna and other blocks of the device shown in figures 1 and 2 are well known from the literature on sonar equipment [2].

 Consider the examples of the sequence of actions of the proposed method.

Example 1. An antenna consists of N = 10 non-directional elements located at a distance of d = 0.25 m. Scanning within the angles θ ₀ ∈. (0.30 ^° ). From formula (4), for n = 1, the frequency f ₀ is determined, setting θ ₀ = 30 ^° , θ = 90 ^° , f ₀ = 4 kHz is obtained. The frequency f _{in is} found using the expression (8): f _in = 8 kHz. Thus, in the frequency range 4 <f <8 kHz, no more than two additional maxima are formed. Calculations show that in fact one additional maximum is formed, equal to the main one.

Сигнал на частоте f₂ не регистрируется. Следовательно, сигнал приходит с направления θ_л, т.к. при изменении частоты приема

При втором варианте приема после обнаружения сигнала подключают с помощью переключателя 6 фильтры 7 и 8, настроенные на частоты f_a=6 кГц, f_b=7,5 кГц, сигнал регистрируется двухканальным регистратором 9 только в канале, настроенном на частоту f_a. Следовательно, сигнал приходит с направления дополнительного максимума по этой частоте, и направление на него -30^o.Figure 3 shows the calculated DN (curve 11), the direction of the main maximum θ ₀ , the direction of the additional maximum, which is to the left of the main one, is denoted by θ _l , in this example θ _l = -30 ^° .
In the first version of the method, detection is performed using the recorder 5. The signal comes from the direction shown in figure 3 by arrow 10. Having connected the filter 4 to clarify the direction, set it to a frequency f ₁ = 6 kHz. The width of the additional maximum, determined by formula (3), is Δθ _0.7 = 6 ^° . The frequency f ₂ should be chosen so as to "tune" from the additional maximum at f = f ₁ , which is achieved by tuning the filter 4 to the frequency f ₂ = 7.5 kHz - curve 12, Fig.3. It can be seen that the diagrams 11 and 12 are fairly spaced, an additional maximum at a frequency f ₂ has a direction

The signal at a frequency f _{2 is} not recorded. Therefore, the signal comes from the direction θ _l , because when changing the frequency of reception

In the second embodiment, after detecting the signal, filters 7 and 8, tuned to the frequencies f _a = 6 kHz, f _b = 7.5 kHz, are connected using switch 6, the signal is registered by the two-channel recorder 9 only in the channel tuned to the frequency f _a . Therefore, the signal comes from the direction of the additional maximum at this frequency, and the direction to it is -30 ^o .

ширина дополнительного максимума Δθ_0,7 = 6^°. Направление прихода сигнала - по стрелке 10.Example 2. N = 10, d = 0.25 m, the case of mechanical scanning, i.e. θ ₀ = 0 ^° .
From the expression (4) is determined f ₀ = 6 kHz, from (8) is f _in = 12 kHz. Therefore, in the range 6 <f <12 kHz, no more than two additional maxima are formed, symmetrically located relative to the main maximum. Calculations show that two additional peaks are formed equal to the main one. The calculated DN is shown in figure 4, curve 13, the direction of the main maximum θ ₀ , the direction of the additional maximum, which is located to the left of the main is indicated by θ _l , to the right -

the width of the additional maximum Δθ _0.7 = 6 ^° . The direction of signal arrival is along arrow 10.

(кривая 14, фиг.4). В соответствии с изображенной на фиг.4 ситуацией сигнал на частоте f₂ не регистрируется, следовательно, направление на него θ_л или θ_п. Сдвигают диаграмму направленности антенны 1 на угол δθ, равный угловому расстоянию между осями дополнительных максимумов на частотах f₁ и f₂, в данном случае

После поворота ДН занимает положение 15, а направления осей максимумов становятся следующими:

причем

Сигнал от цели регистрируется, и направление на него θ_л = -48,5^°. Если бы сигнал отсутствовал, направление на него было бы θ_п = 48,5^°.
Последовательность действий по второму варианту предлагаемого способа в данном примере с двумя дополнительными максимумами отличается от последовательности действий по первому способу тем, что после подключения узкополосных фильтров 7, 8 переключателем 6 и настройки фильтров на частоты f_a, f_b, поворот ДН осуществляется на частоте f_b.According to the first variant of the proposed method, upon detecting the signal, to clarify the direction, connect the filter 4 using the switch 6 and adjust the filter to a frequency f ₁ = 8 kHz. In this case, the position of the additional maxima is θ _l = -48.5 ^° , θ _p = +48.5 ^° . Filter 4 is switched to a frequency f ₂ = 9.7 kHz, providing a shift of the additional maxima to the positions

(curve 14, figure 4). In accordance with the situation depicted in FIG. 4, the signal at a frequency f _{2 is} not recorded, therefore, the direction is θ _l or θ _p . The antenna radiation pattern 1 is shifted by an angle δθ equal to the angular distance between the axes of the additional maxima at frequencies f ₁ and f ₂ , in this case

After turning, the beam occupies position 15, and the directions of the axes of the maxima become the following:

moreover

The signal from the target is recorded, and the direction of it is θ _l = -48.5 ^° . If there was no signal, the direction to it would be θ _n = 48.5 ^° .
The sequence of actions according to the second variant of the proposed method in this example with two additional maxima differs from the sequence of actions according to the first method in that after connecting the narrow-band filters 7, 8 with switch 6 and adjusting the filters to frequencies f _a , f _b , the beam is rotated at frequency f _b .

 It can be seen from the presented examples that, with the help of simple operations and at low hardware costs, it is possible to unambiguously determine the direction to the signal source in the presence of additional radiation pattern maxima.

Literature
1. R.J. Urik. Basics of sonar. L .: Shipbuilding, 1978, p. 347-359.

 2. Handbook of sonar. L .: Shipbuilding, 1988, p. 14-35.

 3. L.V. Orlov, A.A. Shabrov. Hydroacoustic equipment of the fishing fleet. L .: Shipbuilding, 1987, p. 99-101.

 4. V. B. Mitko, A.P. Evtutov, S.E. Gushchin. Hydroacoustic communications and surveillance. L .: Shipbuilding, 1982, p. 33-34.

Claims (2)

1. The method of determining the direction to the source of the hydroacoustic signal, comprising receiving a signal from the direction of the main maximum of the radiation pattern of a multi-element equidistant antenna, characterized in that the signals are received in the frequency range

where c is the speed of sound;
d is the distance between the elements;
θ is the current angle;
θ ₀ is the compensation angle, in which one or two additional maximums symmetrically located relative to the main one are formed in the radiation pattern, the reception frequency is changed until the angular distances between the main and each of the additional maximums change by an angle not less than the angular width of the additional maximum at the level of -3 dB, if the signal is received, the direction of arrival of the signal is determined as the direction of the main maximum, if not accepted, as the direction of the additional one, to clarify which if there are two additional Yelnia maxima at the changed frequency of the reception directivity pattern is rotated to match one of the secondary maxima and the original signal is at a fixed direction is defined as the direction of arrival of the signal from the source, and in its absence - as a direction other additional maximum at the initial reception frequency. 2. The method of determining the direction to the source of the hydroacoustic signal, including receiving a signal from the direction of the main maximum of the radiation pattern of a multi-element equidistant antenna, characterized in that the reception is performed simultaneously at two different frequencies f _a , f _b , with each of the frequencies f _a , f _b satisfies the condition

where c is the speed of sound;
d is the distance between the elements;
θ is the current angle;
θ ₀ is the angle of compensation,
at each frequency in the radiation pattern, one or two additional maxima symmetrically located relative to the main one are formed, and at a frequency f _{b the} angular distance between the main maximum and each of the additional maxima differs from the same distance at a frequency f _a by an angle not less than the angular width of the additional the maximum, if the signal is received at both frequencies, the direction of arrival of the signal is determined as the direction of the main maximum, if at one of the frequencies - as the direction of the additional m maximum at this first frequency, to clarify the direction in the presence of two additional maxima, turn the beam at the second frequency until one of the additional maxima coincides with the direction of the additional maximum at the first frequency, where the signal is received, when a signal is received at the second frequency, this direction is determined as the direction of arrival of the signal from the source, and in the absence, as the direction of another additional maximum at the first frequency.

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