RU2596018C1 - Method for amplitude direction finding of radio signal sources - Google Patents

Abstract

FIELD: radio engineering and communications.

SUBSTANCE: invention can be used in systems for determining direction of radiation source of narrow-band radio signals with known carrier frequency, including in radar, radio navigation, communication. Method includes angular scanning of space by means of a phased antenna array with coherent space-time filtration of signal using spatial filtration of extreme element of array as reference, with arrangement of receiving elements of array at distances from each other, less than value of half-wave, wherein temporal signal filtration is performed using mutually-misaligned phase in range of variation of single-channel correlators, wherein coherent for adjacent angles of direction finding at outputs of multichannel by values of phase misalignment of space-time filter for a row of direction-finding functions, each of which is a dependence of magnitude of corresponding output voltage of filter from angle of direction finding, and direction of signal source is taken as angle at which maximum direction-finding function is achieved, having among other maximum value of main lobe.

EFFECT: high angular resolution of signals.

1 cl, 5 dwg

Description

The invention relates to radio engineering and can be used in systems for determining the direction to the radiation source of narrow-band radio signals with a known carrier frequency, including in radar, radio navigation, communication.

A known method of amplitude direction finding, which consists in scanning the space in a given sector, detecting and processing the received signal and deciding on the results of direction finding of several adjacent angular directions about the direction to the signal source. The output voltage of the receiving device, which detects and processes the received signal, while sequentially changing the angular direction of direction finding, describes the radiation pattern. The direction of its maximum is taken as the direction to the signal source. This is the so-called classical method of amplitude direction finding [Belotserkovsky GB Basics of radar and radar devices. - M .: Owls. Radio, 1975 .-- S. 87-88; Theoretical Foundations of Radar: Textbook. manual for universities / AA. Korostylev, N.F. Klyuev, Yu.A. Miller et al., Ed. V.E. Dulevich. - M .: Owls. Radio, 1978. - S. 260, 262]. Simultaneously with measuring the direction of arrival of the signals, their selection is ensured - resolution along angular coordinates. The width of the radiation pattern determines the resolving capabilities of the amplitude direction finding method and is the main characteristic of the direction finder as an angular selector.

For the technical implementation of the method, a direction finder is used, including an antenna and a receiving device, a beam position control device and a device for determining the maximum output voltage of a direction finder (measuring device).

To increase the signal-to-noise ratio and, as a result, the accuracy of measuring the angular direction of arrival, a coordinated (coherent) temporal processing of the signal is performed in the receiver.

A circular indicator may be used as a measuring device. The sweep of the indicator is synchronized with the angular movement of the radiation pattern. The brightness level of the mark from the signal source on the indicator in the angular coordinate is modulated by the radiation pattern. The maximum brightness of the mark determines the direction to the signal source, and the angular size of the mark is determined by the width of the radiation pattern.

A known method of amplitude direction finding, in which an antenna with continuous opening is used to receive an electromagnetic wave from a signal source [V. Cherdyntsev Radio engineering systems: Textbook. manual for universities. - Mn .: Vysh. school., 1988. - S. 195, 198]. The scanning of space by the radiation pattern is carried out due to the mechanical rotation of the antenna. The sweep of the indicator is carried out by the voltage generated by the sweep generator, which is synchronously connected to the antenna rotation motor. This method does not allow to realize the spatial coordinated signal filtering inherent to direction finders using phased array antennas, which in the presence of internal noise of the receiver leads to a decrease in measurement accuracy and resolution in angular coordinates [A. Korostylev. Spatio-temporal theory of radio systems: Textbook. manual for universities. - M .: Radio and communications, 1987. - S. 83].

The closest analogue of the proposed method is a method of amplitude direction finding with electronic control of the radiation pattern using a phased antenna array [Cherdyntsev V.A. Radio engineering systems: Textbook. manual for universities. - Mn .: Vysh. school., 1988. - S. 124-125, 195, 198]. The method allows both temporal and spatial coherent signal processing.

Due to the discreteness of the aperture of the antenna array, the radiation pattern in the general case has a multilobe nature, which entails the ambiguity of measuring the angular direction of arrival of the signal. When implementing the method, to ensure the presence of one main lobe of the radiation pattern along which direction finding is carried out, the distances between the elements of the antenna array are selected not exceeding half the length of the received wave.

In the method, the direction of reception (direction-finding angle) is controlled by introducing phase shifts into the receiving channels of the phased array, calculated according to the current direction-finding angle.

The phased array antenna, together with the matched receiver, forms a spatio-temporal filter that performs coherent spatio-temporal processing of the received signal.

In the general case, the spatio-temporal filter includes receiving elements of the antenna array, controlled phase-shifting channel elements, an adder of the channel signals and a matched receiver. Controlled phase-shifting channel elements provide direction finder tuning for a given direction of wave reception and can be performed in the form of controlled phase shifters, or in the form of signal mixers with heterodyne voltages having a given phase shift. The matched receiver can be a filtration one, the elements of which are a matched band-pass filter and an amplitude detector, or a correlation one, which consists of two correlators that are in phase detuned by π / 2 in parallel and whose output signals are combined in quadrature. Each correlator consists of an input and reference signal mixer and an integrator (filter) [Theoretical basis of radar: Textbook. manual for universities / A.A. Korostylev, N.F. Klyuev, Yu.A. Miller et al., Ed. V.E. Dulevich. - M .: Owls. Radio, 1978. - S. 76; Korostylev A.A. Spatio-temporal theory of radio systems: Textbook. manual for universities. - M .: Radio and communications, 1987. - S. 36, 37, 82].

A different sequence of spatial and temporal filtering operations is possible. Usually, spatial processing of the field is first performed by opening the antenna, and then temporarily filtering the received signal. Some elements (signal mixer) that implement filtering operations can participate simultaneously in the execution of operations and spatial and temporal filtering.

The task of spatial filtering is to match the phase structure of the incident wave field with the phase structure created by the phase-shifting elements of the antenna array channels by opening the antenna. With full coordination, which is possible only at the direction-finding angle, which coincides with the direction of arrival of the signal, the signals of the receiving channels of the antenna array after passing through the phase-shifting elements become in-phase, and the output voltage of the signal adder becomes maximum. When the direction-finding angle deviates from the angle of arrival of the signal, which is performed by tuning the controlled phase values, the phase matching of the signals in the channels of the grating after passing the phase-shifting elements ceases to be provided, and the total voltage at the output of the phased antenna array decreases, reaching zero values for the phase mismatch of the phases. The dependence of the total voltage at the output of the phased array antenna on the direction-finding angle describes the radiation pattern.

The task of temporal filtering a signal in a direction finder is to measure its individual parameters (delay time and Doppler shift).

Fundamental to the direction finding method is the concrete implementation of the spatial-temporal filtering methods of the received signal and the selective capabilities of the direction finder provided. This is because the absolute phase values of the signal received by each element of the antenna array are unknown. As a result, the spatial-temporal filtering method used, under conditions of an unknown initial signal phase, determines the shape of the dependence of the filter output voltage on the direction-finding angle, i.e., the shape of the radiation pattern.

The known direction finding method for spatio-temporal filtering of a signal with an unknown initial phase uses a method based on the creation of two parallel orthogonal in phase (quadrature) signal processing channels and obtaining the direction finder output signal for the current direction finding direction as a complex signal module that has been filtered in these channels. This approach eliminates the decrease in the signal level at the filter output or even its loss due to inaccurate phase correlator settings, which is possible with single-channel correlation signal processing [A. Korostylev. Spatio-temporal theory of radio systems: Textbook. manual for universities. - M .: Radio and communications, 1987. - S. 36; Cherdyntsev V.A. Radio engineering systems: Textbook. manual for universities. - Mn .: Vysh. school., 1988. - S. 49].

One of the options for implementing the method in the case of sequential spatial and then temporal filtering is the optimal temporal filtering of the signal with an unknown initial phase, performed after the adder of the grating channels. Formally, it boils down to calculating the module of the correlation integral, defined as a vector whose elements are the in-phase and quadrature components of the signal that have passed coherent filtering orthogonal in phase. To form the correlation integral, a matched filter or a quadrature correlation receiver is used.

In another embodiment of the spatial-temporal filtering method used in digital phased array antennas, processing channels orthogonal in phase are created on the basis of preliminary, before processing, conversion of the signal into a complex form [Radar Reference / Ed. M.I. Skolnik. Per from English. under the general ed. V.S. Willow. In 2 books. Book 1. Moscow: Technosphere, 2014 .-- S. 1267, p. 1282-1284]. In this case, an imaginary signal is obtained from a real signal due to a phase shift by π / 2, after which identical operations of multi-channel signal processing are performed in two quadrature channels. After spatio-temporal filtering, the resulting voltage at the output of the direction finder for this case is determined as the modulus of the complex signal that has been filtered in quadrature channels.

The use of the method of temporal filtering a signal based on the calculation of the module of the correlation integral has the advantage associated with maintaining the level of the processed signal regardless of its phase value, however, it is also a disadvantage of the known direction finding method. This is due to the fact that in all variants of the method implementation, due to the use of in-phase orthogonal in-phase and quadrature signals, high-frequency signal filling does not carry useful information, it is excluded from analysis. The high-frequency component of the signal is considered only as a carrier of information. Based on the same premise, to describe the transformation of the signal use only its envelope, recorded in complex form [Korostylev A.A. Spatio-temporal theory of radio systems: Textbook. manual for universities. - M .: Radio and communications, 1987. - S. 34]. As a result of this, in spatial filtering of a signal, the phase structure of the field by the aperture of the antenna is taken into account in the form of phase differences of the field at its various points, and the absolute phase values at these points, determined by the high-frequency component of the received signal, are not taken into account. That is, coherent spatial filtering of the signal, carried out due to phase shifts introduced into the receiving channels of the phased array antenna, is performed accurate to the phase difference of the field at the opening of the antenna.

For this method of coherent spatial filtering, the smallest possible radiation pattern width (highest resolution), determined by the difference between the angles of zero values of the main lobe of the radiation pattern, is determined by the direction-finding angle α calculated relative to the direction of arrival of the signal α _c using the formula sin (α _c ) -sin (α ) = ± λ / L, where λ is the wavelength, L is the magnitude of the aperture of the antenna [Radar Reference / Ed. M.I. Skolnik. Per from English. under the general ed. V.S. Willow. In 2 books. Book 1. Moscow: Technosphere, 2014. - S. 609-611]. That is, the potential (limiting) resolution of the known direction finding method, determined by the distance between the zeros of the main lobe of the radiation pattern along the coordinate sin (α), is 2λ / L.

A disadvantage of the known method of amplitude direction finding is not a sufficiently high resolution, potentially limited to 2λ / L (by zero values of the main lobe of the radiation pattern), which is due to spatial filtering of the received signal accurate to the phase difference between the elements of the aperture of the antenna and not taking into account the instantaneous phase structure of the field the opening of the antenna, determined by the absolute values of the phases at various points of the aperture.

The invention is aimed at solving the problem of increasing the resolution of signals by the angular coordinate by performing coherent spatial filtering of the received signal with an accuracy of the absolute magnitude of the phase of the field along the aperture of the antenna.

The technical result of using the proposed method is to increase the angular resolution of the signals.

Achieving the claimed technical result is based on spatial filtering of the received signal accurate to the absolute magnitude of the phase of the field by opening the antenna. To this end, temporary signal processing, in contrast to the processing method used in the known method of direction finding, is performed by a number of mutually upset in phase in the range of its variation of single-channel correlators. This signal processing method is known in the theory of receiving devices, and is used to measure an unknown signal parameter by a number of single-channel correlators tuned to possible fixed values of the measured parameter [V. Cherdyntsev Radio engineering systems: Textbook. manual for universities. - Mn .: Vysh. school, 1988. S. 87-90; Theoretical Foundations of Radar: Textbook. manual for universities / A.A. Korostylev, N.F. Klyuev, Yu.A. Miller et al., Ed. V.E. Dulevich - M .: Sov. Radio, 1978. - S. 73]. As the measured parameters, the delay time and the Doppler phase shift of the signal reflected from the target are considered. In relation to the invention, the measured signal parameter is its initial phase, the carrier of which is the high-frequency oscillation of the signal.

The output voltage of a single-channel correlator after its detection, in contrast to the output voltage of a quadrature correlation receiver after its quadrature detection, depends on the absolute value of the phase of the input signal. Since temporal filtering of the signal is preceded by tuning the spatial filter using phase-shifting elements to the phase structure of the received field, the magnitude of the output voltages of single-channel correlators reflects the degree of coherence of spatial filtering. As a result of performing coherent spatio-temporal processing of the signal sequentially for various adjacent direction-finding angles, for each single-channel correlator we obtain the dependence of its output voltage on the direction-finding direction (direction-finding function). From the set of direction-finding functions built at the output of the space-time filter, characterizing the degree of spatial filtering coherence for various phase settings of the correlators, it is possible to determine the direction to the signal source. Using the required number of single-channel correlators mutually detuned in phase in the range of its variation, it is possible to ensure the required accuracy of tuning the spatial filter to the phase distribution of the field along the aperture of the antenna.

A similar result occurs if the signal is temporarily filtered by a number of correlators mutually detuned in phase in the spatial filtering channels, before the summation of the antenna array signals. In this case, direction finding functions are built on the outputs of the adders.

Direction finding functions constructed at the output of a spatio-temporal filter in the described manner, by using a number of single-channel correlators mutually detuned in phase in the range of its variation, while maintaining the filtering coherence conditions for various adjacent direction-finding directions, have a significantly smaller width compared to the radiation pattern width obtained using the known method of direction finding.

An additional condition, the fulfillment of which is necessary so that the direction-finding function width is substantially less than the radiation pattern width obtained using the known direction-finding method, is to perform spatial filtering of the signal based on the antenna aperture. In some embodiments of the spatial filtering of the signal in the known method of direction finding, the phase shifts introduced into the channels are counted from the center of the antenna array, that is, spatial filtering is performed, relatively speaking, based on the center of the antenna aperture. In this case, using phase-shifting elements, phase shifts of different polarities relative to the center of the grating are introduced: phase shifts for channels along one side of the center of the grating have a minus sign and on the other side a plus sign [Theoretical basis of radar: Textbook. manual for universities / A.A. Korostylev, N.F. Klyuev, Yu.A. Miller et al., Ed. V.E. Dulevich - M .: Sov. Radio, 1978. - S. 140]. It is possible to filter signals without introducing phase shifts that are bipolar symmetrical with respect to the center of the lattice. In this case, different polarity is introduced into the signals when they are summed - by inverting the signals entering the adder from one of the halves of the antenna array [Cherdyntsev V.A. Radio engineering systems: Textbook. manual for universities. -Mn .: Ab. school., 1988. - S. 120-123]. This method of bipolar spatial filtering leads to the same consequences as the quadrature time processing method described above — the loss of information about the absolute magnitude of the phase of the field by the aperture of the antenna

A theoretical justification for the necessity of fulfilling the condition of spatial filtering of a signal based on the aperture of the antenna aperture and a spatial interpretation of the operations of coherent signal processing are given below (see formulas (7), (8)).

In order to disclose the invention, we give a theoretical justification for the possibility of solving the problem of increasing the angular resolution of signals by performing spatial filtering of the signal accurate to the absolute magnitude of the phase of the field along the aperture of the antenna.

[Чердынцев В.А. Радиотехнические системы: Учеб. пособие для вузов. - Мн.: Выш. шк., 1988. - С. 120; Коростылев А.А. Пространственно-временная теория радиосистем: Учеб. пособие для вузов. - М.: Радио и связь, 1987. - С. 64-85]. При этом также будем считать, что расстояние между приемными элементами антенны для обеспечения единства главного лепестка диаграммы направленности выбрано достаточно малым, что позволяет с целью упрощения математических выкладок заменить дискретное суммирование сигнала по элементам решетки интегрированием по ее раскрыву [Коростылев А.А. Пространственно-временная теория радиосистем: Учеб. пособие для вузов. - М. : Радио и связь, 1987. - С. 83].We assume that the signal source is in the so-called “far zone” and a plane front of an electromagnetic wave of known frequency falls on the antenna array

[Cherdyntsev V.A. Radio engineering systems: Textbook. manual for universities. - Mn .: Vysh. school, 1988. - S. 120; Korostylev A.A. Spatio-temporal theory of radio systems: Textbook. manual for universities. - M .: Radio and communications, 1987. - S. 64-85]. Moreover, we will also assume that the distance between the receiving elements of the antenna to ensure the unity of the main lobe of the radiation pattern is chosen sufficiently small, which allows us to replace the discrete summation of the signal over the elements of the array with integration over its opening to simplify mathematical calculations [Korostylev A.A. Spatio-temporal theory of radio systems: Textbook. manual for universities. - M.: Radio and communications, 1987. - S. 83].

In FIG. 1 shows a distribution diagram of the current phases of the wave front over the antenna opening. In FIG. 1 the following notation is used:

t is the time;

α is the current direction finding angle;

α _c - angle of wave arrival;

t ₃ (α _c , l) - time delay of arrival of the wave front at the 1st antenna aperture point;

L is the aperture size of the antenna;

- период повторения волны.

- period of repetition of the wave.

The initial phase of the wave ϕ _n at the extreme element of the lattice, determined by the high-frequency component of the received signal, is unknown and is a random variable uniformly distributed in the interval [0, 2π].

точке раскрыва, отсчитываемой от края антенны, описывается формулойAntenna elements transform the space-time process into temporary high-frequency electrical oscillations. As in the filtering method used in the known direction finding method, we assume that the received radio signal is narrow-band in the sense of the possibility of replacing the real delay of the arrival time of the wave front to each element of the antenna by taking into account phase shifts determined by the travel time of the wave to these elements [Korostylev A. BUT. Spatio-temporal theory of radio systems: Textbook. manual for universities. - M .: Radio and communications, 1987. - S. 80-81; Cherdyntsev V.A. Radio engineering systems: Textbook. manual for universities. - Mn .: Vysh. Shk., 1988 .-- S. 194; Handbook of Radar / Ed. M.I. Skolnik. Per from English. under the general ed. V.S. Willow. In 2 books. Book 1. Moscow: Technosphere, 2014. - S. 635-636]. The form of the amplitude field distribution is unprincipled due to the possibility of weighted processing of the signal in the channels of the antenna array, in connection with which we assume that the wave has a unit amplitude. Then the voltage created by the wave in an arbitrary

the aperture point, measured from the edge of the antenna, is described by the formula

.

.

The wave received by the elements of the antenna array by means of controlled phase-shifting elements undergoes spatial filtering. The signal is filtered by introducing phase shifts into the receiving channels in accordance with the current direction-finding angle α. In FIG. 1 shows a line of the current phase settings in space (wave front), corresponding to the phase setting of the receiving channels at an angle α relative to the aperture of the antenna.

The signals from the output of the receiving channels enter the adder. The output voltage of the adder is determined by the superposition of voltages at the wave front and on the phase line of the receiving channels of the direction finder.

Consider the case when temporary signal filtering is performed before the summation of the signals of the antenna array.

Let the introduction of phase shifts in the receiving channels be performed using controlled heterodyne voltages, and signal mixers that implement filtering operations are used simultaneously in the execution of operations and spatial and temporal filtering. Then the heterodyne voltages carry information about the phase shifts corresponding to the current direction-finding angle, as well as about the carrier frequency of the signal, and are described by the formula

.

.

where ϕ _g is the initial phase of the heterodyne stresses.

точке раскрыва антенны, осуществляется перемножением напряжений в смесителях и интегрированием на интервале обработки сигнала T_обр:Performing temporary filtering of the signal of each receiving channel of the array corresponding to

the antenna aperture point, is carried out by multiplying the voltages in the mixers and integrating on the signal processing interval T _arr :

.

.

For a signal processing interval T _arr exceeding T / 2, the integration result has the form

,

,

where ϕ _f is the unknown phase component of the video signal after integration.

Suppose that during filtering, due to the choice of the initial phase of the local oscillators ϕ _g , there was a complete compensation of the unknown phase of the signal ϕ _n , that is, the values of the unknown phase component of the video signal are ϕ _f = ± n2π, n = 0, 1, 2, ...

For this case, as a result of integration over the aperture of the antenna with support on the edge of the aperture of the antenna, we obtain the voltage at the output of the adder

Where

The function U (α) is an analogue of the radiation pattern, understood as the distribution of the received field along the angular coordinates. According to the coordinate sin (α), it has a symmetric multilobe structure with one main lobe directed at an angle α _s. The distances along the α axis between the n-th zeros of the function U (α) are calculated from the formula

sin (α _c ) -sin (α) = nλ / 2L, where n = ± 1, ± 2, ...

The width of the main lobe at the zero level is equal to λ / L, that is, for the introduced conditions and the signal processing method, an increased angular resolution of the signal is equal to λ / L compared to the known direction finding method.

We expand the considered signal processing conditions. Suppose that complete compensation for the unknown phase of the signal ϕ _n in the receiving channels is not provided. Then the summation of the output signals of the channels (voltage integration (1) according to the formula (2)) gives the result:

where the value of x is determined by the formula (3).

As an example, to analyze the form of the functions U / (α, ϕ _φ ), calculations were performed for the initial data λ / L = 0.1, α _с = -0.2 [rad]. The calculation results for some characteristic values of the phase ϕ _f are shown in FIG. 2. Here also shows the function of the radiation pattern F (α) of the known method of direction finding, defined as the modulus of the Fourier transform of the field distribution recorded in complex form:

,

,

Where

, вычисляемых для произвольных значений фазы ϕ_ф. Этот вывод подтверждает и аналитическое интегрирование модуля функции

по возможным значениям фазы:Calculations show that the function F (α) is an envelope for the set of modules of functions

calculated for arbitrary values of the phase ϕ _f . This conclusion is confirmed by the analytical integration of the function module

by possible phase values:

.

.

The function F (α) has a maximum in the direction α _s , on the scale sin (α) it is symmetric with respect to the direction of the maximum, and the width of the main lobe at the zero level is 2λ / L. These properties of the function F (α) determine the directional and selective capabilities of the known method of direction finding.

, используемой в предлагаемом способе в качестве альтернативы диаграмме направленности, существенно выше селективных свойств диаграммы направленности F(α), используемой в известном способе пеленгации. Положения нулей пеленгационной функции

относительно направления прихода сигнала определим, приравнивая к нулю выражение (4). В результате получим следующую формулу для нахождения нулей:From the figure in FIG. 2 shows that the selective properties of the direction-finding function

used in the proposed method as an alternative to the radiation pattern, significantly higher than the selective properties of the radiation pattern F (α) used in the known method of direction finding. Positions of the zeros of the direction-finding function

relative to the direction of arrival of the signal we define, equating the expression (4) to zero. As a result, we obtain the following formula for finding zeros:

, нули пеленгационной функции определяются из уравненияFor the main lobe of the radiation pattern that forms when

, zeros of the direction-finding function are determined from the equation

.

.

по ее нулевым значениям, равна λ/L и существенно выше предельной разрешающей способности известного способа. Заметим, что так же существенно выше и точность пеленгования, определяемая крутизной функции

.It follows that regardless of the magnitude of the phase shift ϕ _f , the limiting resolution, determined by the width of the direction-finding function

by its zero values, it is equal to λ / L and significantly higher than the limiting resolution of the known method. Note that the direction finding accuracy determined by the steepness of the function is also significantly higher

.

как пеленгационной характеристики, является зависимость ее формы от величины фазового сдвига ϕ_ф в обрабатываемом сигнале. При полной компенсации неизвестной фазы сигнала ϕ_н, обеспечивающей выполнение равенства нулю величины ϕ_ф, максимум функции

направлен по углу прихода сигнала α_с. С увеличением рассогласования фаз принятого и гетеродинного сигналов, ведущего к росту величины ϕ_ф вплоть до значения π/2, величина максимума функции

монотонно уменьшается. При этом появляется и линейно растет систематическая ошибка пеленга, состоящая в рассогласовании направлений главного лепестка функции и направления прихода сигнала α_с, а также увеличивается величина боковых лепестков функции

. В предельном случае, для значений фазы, кратных π/2, функция

распадается на два лепестка, симметричных относительно направления α_с. При этом полностью исключается прием сигнала с направления α_с.Feature Feature

 as a direction-finding characteristic, is the dependence of its shape on the phase shift ϕ_f in the processed signal. With full compensation of the unknown phase of the signal ϕ_nensuring that the quantity ϕ is equal to zero_fmaximum function

 directed along the angle of arrival of the signal α_from. With an increase in the phase mismatch between the received and heterodyne signals, leading to an increase in ϕ_f up to π / 2, the maximum value of the function

 monotonously decreases. In this case, a systematic bearing error appears and linearly grows, consisting in a mismatch of the directions of the main lobe of the function and the direction of arrival of the signal α_from, and also increases the value of the side lobes of the function

. In the limiting case, for phase values that are multiples of π / 2, the function

 splits into two petals symmetrical with respect to the direction α_from. In this case, signal reception from the α direction is completely excluded_from.

, ограничивающим ее использование для пеленгования, является систематическая ошибка пеленга, обусловленная наличием в фильтруемом сигнале случайной составляющей ϕ_н. Максимальная ошибка пеленга, достигаемая при величине фазового сдвига

, по шкале sin(α) составляет Δ_п≈±0.38λ/L [рад].The main disadvantage of the function

, limiting its use for direction finding, is the systematic bearing error due to the presence of a random component ϕ _n in the filtered signal. Maximum bearing error achieved with phase shift

, on the scale sin (α) is Δ _p ≈ ± 0.38λ / L [rad].

и привести функцию

к известному виду функции F(α) можно разными приемами, которые и используются в различных вариантах технической реализации пространственной фильтрации сигнала в известном способе пеленгования, в том числе:Eliminate bias direction finding function

and bring the function

to a known form of the function F (α), one can use various methods, which are used in various versions of the technical implementation of spatial filtering of a signal in a known direction finding method, including:

1) by presenting the signal in complex form, with performing spatio-temporal filtering in quadrature channels, and calculating the resulting voltage at the output of the direction finder as a module of complex magnitude:

2) due to the use of a spatial filtering signal as a support for the center of the aperture of the antenna, by inverting the phase relative to the center of the aperture of the antenna in the devices introducing phase shifts:

or phase inversion relative to the center of the aperture of the antenna directly in the adder:

In the second variant of eliminating a systematic error based on phase inversion, to eliminate phase modulation of the output signal of the adder by the function cos (ϕ _f ), additionally, quadrature detection is performed after the adder, as a result of which:

, основанный на выполнении параллельной временной обработки принятого сигнала рядом расстроенных относительно друг друга на фиксированное значение вносимого в сигнал фазового сдвига ϕ_г идентичных временных фильтров.In the proposed method of direction finding, in contrast to the known method, the method of reducing the systematic error of direction finding to a given value is used while maintaining the high selective capabilities of the function

based on performing parallel time processing of the received signal in a row of identical time filters introduced into the signal of the phase shift ϕ _{g that} are detuned relative to each other by a fixed value.

имеет повторяющийся по переменной ϕ_ф с периодом π характер. Задаваясь допустимой величиной систематической ошибки пеленга δ_п[рад], необходимое количество пространственно-временных фильтров М для обработки сигнала можно определить по формуле

. При этом, учитывая линейный характер изменения систематической ошибки при изменении фазового сдвига ϕ_ф, расстройку временных фильтров предпочтительно выполнять с регулярным шагом Δ_г величиной Δ_г=π/М. Имея ряд временных фильтров, расстроенных по величине вносимого в обрабатываемый сигнал фазового сдвига ϕ_г в диапазоне изменения фазового сдвига ϕ_ф∈[0, π], на выходе пеленгатора (после детектирования выходных напряжений) получим ряд пеленгационных функций

, неперекрывающихся по направлениям максимумов главных лепестков. Для пеленгации источника сигнала необходимо выбрать одну из них. Учитывая монотонный вид зависимости максимума функции

от величины систематической ошибки пеленгации, для пеленгации источника сигнала следует выбрать пеленгационную функцию, имеющую наибольшую величину главного лепестка. Такой выбор минимизирует систематическую ошибку пеленгации. В результате, в качестве направления на источник сигнала принимают угол, при котором достигается максимум пеленгационной функции, имеющей среди прочих наибольшее значение главного лепестка.This method is based on the fact that the function

has a character repeating in the variable ϕ _f with period π. Given the admissible value of the systematic error of the bearing δ _p [rad], the required number of space-time filters M for signal processing can be determined by the formula

. Moreover, taking into account the linear nature of the change in the systematic error with a change in the phase shift ϕ _f , it is preferable to perform the mismatch of temporary filters with a regular step Δ _g of Δ _g = π / M. Having a number of time filters that are upset by the magnitude of the phase shift ϕ _g introduced into the processed signal in the range of the phase shift ϕ _f ∈ [0, π], we obtain a number of direction finding functions at the direction finder output (after detecting the output voltages)

that do not overlap in the directions of the maxima of the main petals. For direction finding of the signal source, you must select one of them. Given the monotonous dependence of the maximum function

from the magnitude of the systematic error of direction finding, for direction finding of the signal source, you should choose the direction finding function that has the largest value of the main lobe. This choice minimizes the bias of direction finding. As a result, the angle at which the maximum of the direction-finding function, which, among others, has the highest value of the main lobe, is taken as the direction to the signal source.

Note that direction-finding functions, in addition to the dependence of the magnitude of the maximum of the main lobe on the magnitude of the detuning of the phase of the received signal and the tuning phase of the time correlator, have other informative features that can reduce the value of the systematic measurement error. Such signs are the level of their side lobes, as well as their group distribution relative to the direction of the bearing, which can be the basis for the development of statistical methods for assessing the direction of the bearing.

The spatial interpretation of the proposed method of space-time filtering is as follows. With reference to FIG. 1, the filtering method used in the known method of direction finding consists in creating on the normal, corresponding to the angle of direction finding α, two fronts of wave reception, phase-shifted by π / 2. The voltages removed by the receiving elements of the antenna array from these fronts are coherently summed and subjected to joint filtering by a matched receiver. The result of such a spatio-temporal filtering with varying direction-finding angle α is the well-known radiation pattern F (α). At the same time, quadrature voltage detection in a matched receiver leads to a loss of information about the absolute values of the field phase by the aperture of the antenna. A spatial filtering of the signal based on the center of the antenna aperture leads to a similar result. In this case, the introduction of phase shifts of different polarities relative to the center of the grating into the received signal corresponds to the formation of two fronts of wave reception, phase-shifted by π. Coherent summation of the voltages removed by the receiving elements of the lattice from these fronts also leads to the loss of information about the absolute values of the phase of the field along the aperture of the antenna.

, по которым и принимается решение о направлении прихода радиосигнала.The proposed filtering method allows you to create a series of mutually detuned direction-finding fronts in space on the interval of phase change, tied to the edge of the antenna aperture. Spatio-temporal filtering using single-channel correlators undergoes voltages taken by the elements of the antenna array from each of these fronts, while the absolute values of the phase of the field along the aperture of the antenna are stored. The output voltages of the filters are detected, as a result of which, according to the results of varying the direction-finding angle α, a number of direction-finding functions are formed

by which a decision is made on the direction of arrival of the radio signal.

.The discrete implementation of the spatio-temporal filtering option described by formulas (1), (2) in the proposed direction finding method assumes the presence of an N-element antenna array, to which M hardware-identical spatially-temporal filters that are phase-unbalanced are connected in parallel. Each spatio-temporal filter consists of N mixers of the received and heterodyne voltage mixers and integrators that simultaneously realize the spatial and temporal filtering functions, which are connected in series to the elements of the antenna array. The integration results are fed to the adder of the signals N of the receiving channels of the space-time filter. Space-time filters differ in the magnitude of the fixed phase shift introduced into the heterodyne voltage ϕ _gj = jΔ _g , j = 0.1, ... M-1. At the outputs of their adders after detection receive analyzed direction-finding functions

.

The construction of a spatio-temporal filter according to the described scheme, due to the fact that temporal processing is combined with spatial one due to the use of common mixers, requires N × M mixers, N × M integrators, as well as M adders and M detectors. Due to the large number of high-frequency devices, this circuit may have certain difficulties in practical implementation.

For reasons of simplifying the hardware implementation of the proposed method of direction finding, the spatial and temporal processing of the signal, as in the known method, can be changed.

Consider the case when the temporal filtering of a signal is performed after its spatial filtering.

Let spatial filtering be performed on controlled phase shifters with summation of the signals of the receiving channels of the grating at a high frequency. Temporary signal processing is performed after the adder using a series of up-phase single-channel correlators. For this case, the formulas for describing the processing processes have the form:

точке раскрыва антенны, имеют вид:- voltage at the outputs of the phase shifters in the receiving channels of the lattice corresponding

antenna aperture point, have the form:

;

;

- the signal at the output of the adder of these voltages is a high-frequency oscillation with an unknown initial phase and has the form:

,

,

where the value of x is determined by the formula (3),

и интегрирования в корреляционном приемнике, выходной сигнал одноканального коррелятора имеет вид- after heterodyning the output signal of the adder reference voltage

and integration in the correlation receiver, the output signal of the single-channel correlator has the form

.

.

The result obtained completely coincides with the result obtained for performing first temporary and then spatial filtering (see formula (4)). However, performing first spatial and then temporal filtering of the signal may be more preferable for reasons of hardware implementation. The discrete implementation of such a filtering sequence involves the dilution of the processed signal into M parallel channels of temporal filtering upset by phase ϕ _g after spatial filtering. This option for constructing a spatio-temporal filter requires N high-frequency phase shifters, one adder and M single-channel correlators, each of which contains a series-connected mixer of the total and common heterodyne signals and an integrator on the signal processing interval T _arr . In this case, the phase detuning of the correlators can be carried out both by introducing phase shifts ϕ _gj = jΔ _r , j = 0.1, ... M-1 into the heterodyne voltage of the correlators, and by using phase shifters with fixed phase shifts ϕ _gj at the inputs of the correlators. At the output of each of the M single-channel correlators, an envelope detector must be turned on to construct the direction-finding function.

In general, making the transition from considering the continuous field distribution over the antenna opening, which made it possible to simplify the theoretical justification of the invention, to the discrete field distribution over the receiving elements of the antenna array, the proposed direction finding method is described by the following set of actions and conditions for their implementation.

As in the known method, for direction finding use a phased antenna array with the placement of the receiving elements at distances from each other smaller than the half-wave. In a given scanning sector, at each subsequent direction-finding angle, spatial-temporal filtering of the signal is performed. The spatial filter includes receiving antenna elements, coupled to them controlled devices for introducing a phase shift grating into the signals of the receiving channels corresponding to the current direction-finding angle, performed on phase shifters or mixers of the received signal with heterodyne voltages, as well as a channel voltage adder.

In contrast to the known method of direction finding, in which it is possible to perform spatial filtering of a signal based on the center of the aperture of the antenna, in the proposed method, spatial filtering is performed based on the edge of the aperture of the antenna, that is, the phase shifts introduced into the channels are counted from some extreme receiving element lattice. In view of the accepted assumption about the narrowband signal of the direction-finding signal, the specific choice of the extreme element of the array is not fundamental. In addition, the summation of the signals of the receiving channels of the antenna array is performed without their inversion relative to the Central channel.

Also, in contrast to the known method, for the temporal filtering of a signal, a series of parallel-connected mutually disordered in phase on the interval of its change single-channel correlators is used. Considering the subsequent, after filtering, signal detection, leading to the inversion of negative voltage values, the phase change range, requiring overlapping by mutually detuned phase single-channel correlators, is [0, π]. The correlation step detuning step should provide a satisfactory value for the systematic error in measuring the angular direction of the wave source.

The technical implementation of each single-channel correlator is a sequentially connected mixer of the processed and heterodyne signals and an integrator on the signal processing interval T _o6p exceeding the half-wave period of the T / 2 wave. Phase mismatch of the correlators can be performed both by introducing fixed phase shifts into the heterodyne voltages of the mixers, and by using phase shifters with fixed phase shifts at the inputs of the correlators.

Temporal filtering of a signal using a series of mutually detuned in phase phase single-channel correlators can be performed both after spatial filtering and before spatial filtering (before summing the signals of the receiving channels of the antenna array).

In the case of the digital implementation of temporal signal filtering, the hardware equivalent of a series of parallel-connected mutually detuned in phase single-channel correlators working simultaneously is the use of one digital correlator that provides signal filtering with a time-sequential change in phase mismatch.

In contrast to the known direction finding method, in the proposed method, temporal filtering of the signal for adjacent direction finding angles is performed coherently, which ensures that the direction finding conditions are identical up to the value of the initial phase of the signal being processed, which is necessary for constructing direction finding functions. This requirement is due to the fact that the unknown initial phase ϕ _{n of the} high _- frequency oscillation at the input of the direction finder (on the supporting element of the antenna array) constantly changes as the wave arrives at the aperture. The heterodyning of the received signal during its temporary processing by the reference voltage of the same frequency as the received oscillation, with a certain initial phase ϕ _g, allows us to fix the ratio of the phases ϕ _n and ϕ _g on the time interval of signal processing T _arr for the current direction finding angle α. However, to construct the direction-finding function, it is necessary that for each next (adjacent) value of the angle α specified during scanning, the ratio of the initial phases ϕ _n and ϕ _g does not change. This can be achieved if, for each adjacent direction-finding angle, a correcting phase addition of the same magnitude as the phase addition of the incident wave, which has run over the period between the start of signal processing at the current and previous values of the angle α, is introduced into the heterodyne voltage of the correlator, i.e., to ensure the coherence of the time signal processing at adjacent direction-finding angles, at least within the angular sector of the direction-finding function formation. To ensure complete coherence of the temporal processing of the signal at adjacent direction-finding angles, it is sufficient to perform it after a period of time that is a multiple of the half-period of the T / 2 wave.

Also, unlike the known method, as a result of signal processing and detection, at the outputs of a multi-channel spatial-temporal filter according to the phase mismatch values, a series of direction-finding functions are formed that represent the dependence of the module of the corresponding filter output voltage (i.e., the output voltage of each correlator, in the case of sequential spatial - temporal filtering, or of each adder - in the case of sequential temporal and spatial filtering) from the direction-finding angle. Based on the analysis of the formed direction-finding functions, the angle at which the maximum direction-finding function is achieved, which, among others, has the largest magnitude of the main lobe, is taken as the direction to the signal source.

The described method of direction finding provides a high angular resolution of direction finding signals at a given (in the case of using a sufficient number of single-channel correlators) level of systematic error in measuring the angle.

Further, the invention is disclosed by the example of the technical implementation of the proposed method of direction finding, using the hardware-economical option of spatio-temporal filtering described above with sequential spatial signal processing using phase shifters and temporal processing using M unbalanced phase correlation receivers.

The structural diagram of the direction finder is shown in FIG. 3, where indicated:

1 - antenna array of N receiving elements having the numbering i = 0, 1, ..., N-1;

2 - controlled phase shifter;

3 - control unit phase shifters;

4 - adder;

5.0, 5.1, .., 5.j, ..., 5.M - single-channel correlation receivers;

6 - mixer;

7 - integrator;

8 - phase-shifting element of the reference voltage of the correlator;

9 - phase-shifting element with a phase shift of π / 2;

10 - shaper of the reference voltage u _op (t);

11 - quadrature envelope detector;

12 - envelope detector;

13 - block forming direction-finding characteristics;

14 - a decisive device;

15 is a scan control device.

The principle of operation of the direction finder is as follows. At the receiving elements of the antenna array 1, placed with a step d = L / N, not exceeding λ / 2, from the direction α _s to be measured, a wave arrives. The unknown initial phase of the wave received by the zero (reference) element of the lattice is equal to ϕ _n . The voltages at the outputs of the elements of the antenna array are described by the formula

.

.

, вырабатываемые блоком управления фазовращателями 3, соответствующие текущему значению варьируемого угла пеленгования α. Напряжение на выходе фазовращателя, присоединенного к i-му приемному элементу антенной решетки имеет видUsing controlled phase shifters 2, phase shifts are introduced into voltages u (t, i)

generated by the control unit phase shifters 3, corresponding to the current value of the variable angle of direction finding α. The voltage at the output of the phase shifter connected to the i-th receiving element of the antenna array has the form

.

.

The output voltages of the phase shifters are summed in the adder 4:

.

.

The signal from the output of the adder is fed to M parallel-connected single-channel correlation receivers 5.j, j = 0.1, ... M-1, tuned respectively to fixed values of the phase shift ϕ _gj = jΔ _g , as well as to the unnumbered input of the quadrature channel of the signal processing.

и интегратор на интервале обработки сигнала Т_обр.Each single-channel correlation receiver includes a mixer 6 of the output signal of the adder and heterodyne voltage

and an integrator on the signal processing interval T _arr .

The output voltages of the correlators for the current value of the direction finding angle α are calculated by the formula

.

.

, вырабатываемое формирователем 10, фиксированных значений фазовой расстройки корреляторов ϕ_гj.Heterodyne stresses are formed by introducing phase-shifting elements 8 into the common reference voltage

generated by the shaper 10, fixed values of the phase _{mismatch of the} correlators ϕ _gj .

(см. формулу (6)). Напряжение u_д.кв для текущего значения варьируемого угла пеленгования α представляет собой значение диаграммы направленности F(α) пеленгатора, реализующего известный способ пеленгации.The quadrature processing channel is formed by a mixer 6, in which the heterodyne voltage of one of the single-channel correlation receivers, in this case, the correlator 5.1, and the integrator 7 are used as the heterodyne voltage, and the integrator 7. The output voltage of the quadrature channel u _kv is input to the quadrature detector 11 . On its other input is the common-mode voltage u _s from the output of the receiver 5.0. The voltage at the output of the quadrature detector u _d.sq. is defined as the square root of the sum of the squares of the input voltages:

(see formula (6)). The voltage u _d.s.c for the current value of the variable direction-finding angle α is the value of the direction-finding pattern F (α) of the direction finder that implements the known method of direction-finding.

и диаграмма направленности F(α).The output voltages of the correlators are detected using detectors 12 and fed to the input of the direction-finding function generation unit 13. In the direction-forming function generation unit, when the angle α is varied, M direction-finding functions are formed

and the radiation pattern F (α).

The selection of one of the direction-finding functions for deciding on the direction of arrival of the signal is carried out in the resolver 14 according to the criterion of the maximum value of the main lobe of the direction-finding function. The angular direction α _s to the signal source is taken equal to the angular direction of the main lobe of the selected direction finding function. The function F (α) is used in this case to compare the selective capabilities of the known and proposed methods of direction finding.

The scanning control device 15 at time intervals that are multiples of the half-period of the received radio wave sets the next values of the direction-finding angle α and synchronizes the operation of the spatial and temporal filtering devices and the formation of direction-finding characteristics.

для следующих исходных данных: α_с=-0.2 [рад], N=20, L=0.3, λ=0.03, Δ_г=π/10, М=10. При этом величина неизвестного значения начальной фазы волны на крайнем элементе антенной решетки принята равной ϕ_н=π/20, что обеспечивает тестирование работы схемы пеленгатора в наихудших условиях - при попадании фазы принятого сигнала ϕ_н на середину межканального фазового интервала Δ_г. Количество корреляционных приемников М выбрано исходя из необходимости обеспечения систематической ошибки пеленгования не более 0.004 [рад], или 2.0% от ширины диаграммы направленности F(α) по уровню первых нулей.To assess the performance of the proposed direction finder circuit, direction-finding functions were calculated

 for the following source data: α_from= -0.2 [rad], N = 20, L = 0.3, λ = 0.03, Δ_g= π / 10, M = 10. The value of the unknown value of the initial phase of the wave at the extreme element of the antenna array is taken equal to ϕ_n= π / 20, which provides testing the operation of the direction finder circuit in the worst conditions - when the phase of the received signal ϕ_n in the middle of the interchannel phase interval Δ_g. The number of correlation receivers M is selected based on the need to ensure a systematic direction finding error of not more than 0.004 [rad], or 2.0% of the width of the radiation pattern F (α) at the level of the first zeros.

в сопоставлении с диаграммой направленности F(α), получаемой на основе известного способа пеленгования, приведены на фиг. 4. Функция F(α) обозначена штриховой а функции

- сплошными линиями. Пеленгационные функции рассчитаны в предположении, что выполнено требование обеспечения когерентности временной фильтрации сигнала в смежных направлениях пеленгования.Results of direction finding functions

in comparison with the radiation pattern F (α) obtained on the basis of the known direction finding method, are shown in FIG. 4. The function F (α) is indicated by the dashed function

- solid lines. Direction finding functions are calculated under the assumption that the requirement of ensuring coherence of the temporal filtering of the signal in adjacent directions of direction finding is fulfilled.

,

, сформированных, соответственно, корреляционными каналами с номерами 5.0 и 5.1 (они для заданного значения начальной фазы ϕ_н=π/20 симметричны). В этих каналах достигается максимальный уровень главных лепестков пеленгационных функций, превышающий на ~2,5% величину главного лепестка пеленгационных функций

,

, сформированных соседними (по фазовой расстройке) корреляционным каналами 5.2 и 5.9. Величина измеренного по выбранным пеленгационным функциям направления на источник сигнала равна соответственно - 0.1961 [рад] и - 0.2039 [рад]. То есть направление на источник сигнала определено с удовлетворительной (заданной) систематической погрешностью измерения, которая не превысила 2.0% от ширины диаграммы направленности F(α).As follows from the calculations, one of the functions should be used as direction finding functions for estimating the angular direction to the wave source α _s

,

formed, respectively, by correlation channels with numbers 5.0 and 5.1 (they are symmetric for a given value of the initial phase ϕ _n = π / 20). In these channels, the maximum level of the main lobes of direction-finding functions is reached, which exceeds ~ 2.5% the value of the main lobe of direction-finding functions

,

formed by adjacent (by phase mismatch) correlation channels 5.2 and 5.9. The value of the direction to the signal source measured by the selected direction-finding functions is equal to - 0.1961 [rad] and - 0.2039 [rad]. That is, the direction to the signal source is determined with a satisfactory (predetermined) systematic measurement error, which did not exceed 2.0% of the radiation pattern width F (α).

The signal resolution at zero values of the main lobe of the direction-finding function U ₀ (α) is 0.2461-0.1461 = 0.1 [rad]. The known method of direction finding provides a resolution of 0.3-0.1 = 0.2 [rad]. That is, the required technical result of using the proposed method is achieved.

Additionally, testing the above direction finder circuit with predetermined parameters was performed for the case of receiving signals from two sources located in the angular sector less than λ / L [rad], which determines the maximum resolution capabilities of the known direction finding method. As the initial data, it was assumed that the directions to the first and second signal sources are set, respectively, by the angles α _c1 = -0.28 [rad] and α _c2 = -0.12 [rad], and the values of the initial phases of the received waves are equal, respectively, ϕ _н1 = π / 20 and ϕ _H2 = π / 3.

, сформированная на выходе корреляционного канала 5.2, обеспечивает полное разрешение каждого из двух источников сигналов с удовлетворительным уровнем систематической погрешности измерения, в то время как применение известного способа пеленгации не позволяет разрешить сигналы.The calculation results of direction finding functions are shown in FIG. 5. The calculations confirm the increased selective capabilities of the proposed method of direction finding. So, direction finding function

, formed at the output of the correlation channel 5.2, provides full resolution of each of the two signal sources with a satisfactory level of systematic measurement error, while the application of the known method of direction finding does not allow to resolve the signals.

The performed calculations confirm the possibility of technical implementation of the angular selector with high resolution.

Thus, the use of the proposed method of direction finding provides an increase in the angular resolution of the signals.

Claims (1)

A method for amplitude direction finding of narrowband radio signal sources, which consists in angular scanning of space using a phased array antenna with coherent spatio-temporal filtering of the signal, using spatial filtering of the extreme element of the array as a reference, with the arrangement of receiving elements of the array at distances from each other less than half-waves, characterized in that the temporal filtering of the signal is performed using mutually detuned in phase in the range its changes in single-channel correlators, while a series of direction-finding functions are formed coherently for adjacent direction-finding angles at the outputs of a multi-channel spatial-temporal filter mismatch, each of which represents the dependence of the module of the corresponding output voltage of the filter on the direction-finding angle, and as a direction to the signal source take the angle at which the maximum direction finding function is achieved, having among others the largest magnitude of the main lobe.

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