RU2271057C2 - Adaptive antenna array compensating for results of directivity pattern scanning - Google Patents

Abstract

FIELD: data reception and processing in noise environment, for instance, in radar location.

SUBSTANCE: proposed adaptive antenna array that functions to compensate for results of scanning has N array antennas, items of weighting coefficients, adaptive processor, and adder; in addition, it has newly introduced N x D items of weighting coefficients compensating for results of scanning directivity pattern, where G is quantity of probable noise sources.

EFFECT: enhanced efficiency of spatial noise suppression.

1 cl, 7 dwg

Description

The invention relates to the field of reception and processing of information under the influence of interference and, in particular, to radar.

Known multi-element adaptive antenna array with a controlled radiation pattern [1, p.202, Fig.5.17], which consists of N spatial channels. Each of the spatial channels includes serially connected: antenna array element, correlation mixer, amplifier, integrating filter, radiation pattern control element, mixer, adder.

The output of each spatial channel is connected to the corresponding input of the adder, the output of which is the output of the antenna array. The output of each of the elements of the antenna array is connected to the second input of the mixer of the corresponding spatial channel. At the second input of the radiation pattern control element of each of the spatial channels, a corresponding radiation pattern control signal is input. The output of the antenna array is connected to all second inputs of the correlation mixers.

The operating mode of this device assumes the spatial static nature of the radiation pattern and the source of interference. In the case of a spatial mismatch of the maximum of the radiation pattern and the source of interference that varies over the adaptation interval of the antenna array, the formation of dips in the radiation pattern will occur with an error. This will result in poor spatial interference suppression.

Thus, the disadvantage of this device is the low spatial interference suppression efficiency.

The closest to the invention in terms of features is the device of an adaptive antenna array [2, p.338, Fig.5.10], the structural diagram of which is shown in figure 1.

The input of the adaptive antenna array is N elements of the antenna array 1, the outputs of which are connected to the corresponding first inputs of N elements of the weighting factors 2 and the corresponding inputs of the adaptive processor 3. To each of the controlled inputs of the elements of the weighting factors 2 is connected the corresponding output of the adaptive processor 3. The outputs of the elements of the weighting factors 2 are the corresponding inputs of the adder 4, which is the output of the adaptive antenna array.

Weighting factors provide control of the amplitude-phase distribution of the elements of the antenna array, that is, they are complex.

The choice of a prototype with digital control is due to a number of advantages. Currently, adaptive antenna arrays use analog control loops along with digital ones. The advantage of analog control loops is the ability to process signals in real time, a large dynamic range of signals, and ease of implementation. However, the analog control loops are large and energy efficient. Therefore, their use in adaptive antenna arrays with a large number of antenna elements 1 causes difficulties in the implementation of such adaptive antenna arrays. Additional difficulties in the implementation of analog control loops arise due to the nonlinearity of the elements of the feeder path, control loops and weighting factors. Therefore, to address these shortcomings in adaptive antenna arrays, an adaptive digital processor is used.

The block diagram of the adaptive processor 3 shown in figure 2, contains:

UVX - a device for sampling and storing signals;

ADC - analog-to-digital converter;

Computer - electronic computer;

DAC - Digital-to-Analog Converter.

The adaptive processor 3 shown in FIG. 2 is based on a computing device — an electronic computer (computer). Such a processor only works with digital signals. Therefore, an analog-to-digital converter (ADC) is provided at the input of the processor, and a digital-to-analog converter (DAC) at the input. To assess the weighting coefficients, a correlation matrix of interference is used. To this end, before the ADC include a device for sampling and storage (UX) signals. This device is designed to evaluate the signal at a specific point in time and store this value for some time. In the case when the signal being processed is relatively low-frequency, that is, the period of the carrier oscillations is much longer than the time for computer operations, then the digital processor will have time to monitor the high-frequency signal in real time and the signal sampling and storage device will not be needed.

The adaptive processor determines 3 weighting coefficients according to various optimality criteria. The most well-known optimality criteria when calculating weighting coefficients [2, p.151] include:

1) minimum standard error;

2) maximum signal / signal (noise + interference) ratio;

3) maximum likelihood ratio;

4) minimum output power.

There is an almost complete identity of the ratios for calculating the optimal weighting factors W _opt , since all formulas for various criteria can be represented as:

where β is a constant coefficient;

R ^-1 is the inverse correlation matrix;

S _c is a vector describing the direction of arrival of the useful signal.

In the case when the useful signal and the interference are separated in space by more than the width of the radiation pattern (i.e., the interference affects the side lobes) R≈R _xx , where R _xx is the correlation matrix of interference calculated by the formula [2, p.75 , formula (1.200)]:

By definition, the interference correlation matrix R _xx must be calculated by averaging over implementations. But there is only one implementation. Therefore, under the assumption of ergodicity of a random process [3, p. 124], according to which there is only one implementation, the interference correlation matrix R _{xx is} calculated by averaging over time.

In all known devices, when applying these criteria, it is assumed that there is no spatial mismatch between the maximum of the radiation pattern and the source of interference in the averaging interval of the correlation matrix of interference. In practice, a mismatch can be created either by scanning the radiation pattern, or by changing the angular coordinates of the interference source relative to the radar, or if these reasons exist simultaneously. However, the calculations show that, on the averaging interval of the correlation matrix of interference, a change in the angular coordinates of the interference source relative to the radar introduces a slight angular mismatch and can be neglected in most cases. The scanning of the radiation pattern introduces significant errors in the calculation of the correlation matrix of interference R _xx , which reduces the effectiveness of spatial interference suppression in the radar.

The expression for the (m, n) element of the interference correlation matrix R _xx calculated under the conditions of scanning the radiation pattern on the averaging interval represented by the sequence {t ₁ , t ₂ , ..., t _L } will have, in accordance with formula (2), view

where i is the number of the time reference;

- пространственная структура помехи, принятой m-м элементом антенной решетки 1 в момент времени t_i;

- spatial structure of the interference received by the m-th element of the antenna array 1 at time t _i ;

- значение фазы в пространственной структуре помехи, принятой m-м элементом антенной решетки 1 в момент времени t_i, без влияния сканирования диаграммы направленности;

- the phase value in the spatial structure of the interference received by the m-th element of the antenna array 1 at time t _i , without the influence of the radiation pattern scan;

- значение в момент времени t_i в m-м элементе антенной решетки 1 фазовой составляющей в пространственной структуре помехи, вызванной влиянием сканирования диаграммы направленности;

- the value at time t _i in the m-th element of the antenna array 1 of the phase component in the spatial structure of the interference caused by the influence of the scanning pattern;

- пространственная структура помехи, принятой n-м элементом антенной решетки 1 в момент времени t_i;

- spatial structure of the interference received by the nth element of the antenna array 1 at time t _i ;

- значение в момент времени t_i в n-м элементе антенной решетки 1 фазовой составляющей в пространственной структуре помехи, вызванной влиянием сканирования диаграммы направленности;

- the value at time t _i in the nth element of the antenna array 1 of the phase component in the spatial structure of the interference caused by the influence of the scanning pattern;

- значение фазы в пространственной структуре помехи, принятой n-м элементом антенной решетки 1 в момент времени t_i, без влияния сканирования диаграммы направленности;

- the phase value in the spatial structure of the interference received by the nth element of the antenna array 1 at time t _i , without the influence of the radiation pattern scan;

X _m (t _i ) is the temporal structure of the interference received by the mth element of the antenna array 1 at time t _i ;

X _n (t _i ) is the temporal structure of the interference received by the nth element of the antenna array 1 at time t _i ;

* - operation of complex pairing.

приводящий к ошибкам в расчете корреляционной матрицы помех R_xx. При статическом условии, т.е. без сканирования диаграммы направленности, выражение для (m,n) элемента корреляционной матрицы помех R_xx на интервале усреднения, представленного последовательностью {t₁,t₂,...,t_L], будет в соответствии с формулой (2) иметь видFormula (3) shows that at each time t _{i the} term of the formed sum (3) has an additional factor

leading to errors in the calculation of the correlation matrix of interference R _xx . Under the static condition, i.e. without scanning the radiation pattern, the expression for the (m, n) element of the interference correlation matrix R _xx on the averaging interval represented by the sequence {t ₁ , t ₂ , ..., t _L ] will, in accordance with formula (2), take the form

вызывающие ошибки в расчете корреляционной матрицы помех R_xx. Это объясняется тем, что неподвижность диаграммы направленности на интервале усреднения, представленного последовательностью {t₁,t₂,...,t_L}, не вызывает появления фазовых набегов, которые образуются при сканировании диаграммы направленности.The difference between formula (4) and formula (3) is that the terms in (4) do not have additional factors

causing errors in calculating the correlation matrix of interference R _xx . This is due to the fact that the immobility of the radiation pattern in the averaging interval represented by the sequence {t ₁ , t ₂ , ..., t _L } does not cause the appearance of phase raids that are formed when scanning the radiation pattern.

Thus, when scanning the radiation pattern, phase incursions caused by scanning the radiation pattern at different points in time in the elements of the antenna array 1 will be different. This leads to the fact that the obtained correlation matrix of interference R _xx will differ from the correlation matrix of interference obtained in static conditions, i.e. without scanning the radiation pattern, which reduces the effectiveness of spatial interference suppression.

.Figure 3 shows the dependency graphs of a fixed radiation pattern of an adaptive antenna array under the influence of interference [2, Fig. 5.1, p. 328] and [4, Fig. 17.8, p. 388]. On the ordinate axis, the letter F denotes the values of the radiation pattern. On the x-axis, the letter Θ indicates the values of the spatial angles. The arrows with the inscription "Interference" show the angular directions to the source of interference at time t ₁ , t ₂ and t _L. The spatial angles of directions to the source of interference at the indicated times are indicated, respectively,

.

The graphic material presented is an illustration of the suppression of noise by an adaptive antenna array in the absence of radiation pattern scanning. It is shown that at times t ₁ , t ₂ and t _{L the} direction of the interference radiation source does not change. According to the calculated interference correlation matrix R _{xx, the} adaptive processor 3 generates weight coefficients W _opt , which ensure the formation in the radiation pattern of the dip to a zero value in the direction to the interference source. The interpretation of the adaptive antenna array consists of the following sequence of actions:

1. The initial radiation pattern of the antenna array F ₀ (θ) is determined.

2. The direction to the source of interference θ _{P is} determined by the received interfering signal.

3. A directional pattern of the adaptive antenna array is formed with a dip in the direction of the interference source.

However, when scanning the radiation pattern, the work of the adaptive antenna array has differences, which are reflected in figure 4.

.Figure 4 shows the graphs of the dependence of the scanning radiation pattern of the adaptive antenna array when exposed to interference. On the ordinate axis, the letter F denotes the values of the radiation pattern. On the x-axis, the letter Θ indicates the values of the spatial angles. The arrows with the inscription "Interference" show the angular directions to the source of interference at time t ₁ , t ₂ and t _L. The spatial angles of directions to the source of interference at the indicated times are indicated, respectively,

.

It is shown that at times t ₁ , t ₂ and t _{L, the} direction of the interference radiation source changes as a result of scanning the radiation pattern. According to the calculated interference correlation matrix R _{xx, the} adaptive processor 3 generates weighting factors W _opt , which, as shown in the lower graph of FIG. 4, create a dip in the radiation pattern that does not ensure reaching a zero value in the direction to the interference source. This confirms a decrease in the spatial interference suppression efficiency compared to spatial interference suppression by an adaptive antenna array with a fixed radiation pattern.

Figure 5 shows the dependence of the energy utilization coefficient on the angular parameter [5, p. 115, p. 311] according to the results of modeling an adaptive antenna array.

The energy utilization coefficient shows how much of the useful signal energy is used “useful” in the presence of external interference. It characterizes the energy loss of the useful signal when processing the useful signal against interference compared with the energy loss of the useful signal when processing the useful signal due to intrinsic noise.

On the ordinate axis, the energy utilization coefficient, measured in dB, is indicated by K _uΔ , dB. On the abscissa axis, the letter u denotes the dimensionless angular parameter. The angular displacements caused by scanning the radiation pattern are indicated: Δu = -0.01 and Δu = -0.001. The curves indicated by the number 1 correspond to the effects of interference exceeding the intrinsic noise by 20 dB, the number 2 by 30 dB, the number 3 by 40 dB and the number 4 by 50 dB. The simulation results prove that an increase in the angular mismatch caused by scanning the radiation pattern, all other things being equal, causes a deterioration in the efficiency of spatial interference suppression. For example, for interference characterized by a level of 50 dB, which corresponds to the curve indicated by the number 4, the decrease in the suppression efficiency with a mismatch Δu = -0.001 was 7 dB and with a mismatch Δu = -0.01 it was 13 dB.

Thus, the disadvantage of the considered device, the closest to the invention, is the reduction in the efficiency of spatial interference suppression when scanning the radiation pattern.

The technical result of the invention is the creation of an adaptive antenna array that compensates for the result of scanning the radiation pattern, which will increase the efficiency of spatial interference suppression of the adaptive antenna array when scanning the radiation pattern.

The technical result is achieved by the fact that in the prototype, consisting of N elements of the antenna array, N elements of the weight coefficients, the adaptive processor and the adder, (N × D) elements of the weight coefficients of the compensation for scanning the radiation pattern are additionally introduced, D determines the number of possible sources of interference.

The invention is illustrated by drawings, in which Fig. 1 shows a block diagram of a device closest to the invention - an adaptive antenna array, Fig. 2 shows a block diagram of an adaptive processor, Fig. 3 shows graphs of a fixed radiation pattern of an adaptive antenna array under the influence of interference , Fig. 4 shows graphs of the dependence of the scanning radiation pattern of the adaptive antenna array under the influence of interference, Fig. 5 shows graphs of the dependence of the utilization coefficient Bani energy in the prior art when subjected to interference, Figure 6 shows a block diagram of an adaptive array antenna, compensating the result of scanning the radiation pattern, Figure 7 shows graphs of the energy ratio in the adaptive array antenna, the compensating scan result directivity pattern.

An adaptive antenna array that compensates for the result of scanning the radiation pattern, the structural diagram of which is shown in Fig.6, consists of N elements of the antenna array 1, N elements of the weighting coefficients 2, adaptive processor 3, the adder 4, introduced (N × D) elements of the weighting compensation coefficients radiation pattern scan results 5, D determines the number of possible sources of interference.

The input of the adaptive antenna array, compensating for the result of scanning the radiation pattern, are the elements of the antenna array 1, the outputs of which are connected to the corresponding first inputs of the N elements of the weight coefficients 2. To each of the controlled inputs of the elements of the weight coefficients 2 is connected the corresponding output of the adaptive processor 3. The outputs of the elements of the weight coefficients 2 are the corresponding inputs of the adder 4, which is the output of the adaptive antenna array that compensates for the result of scanning Grams orientation.

Each of the outputs of the elements of the antenna array 1 is connected to the corresponding first inputs (N × D) of the elements 5. To each of the controlled inputs (N × D) of the elements 5 are connected the corresponding (N × D) outputs of the adaptive processor 3. Each of the outputs of the elements 5 is connected with separate corresponding (N × D) inputs of the adaptive processor 3.

The work of an adaptive antenna array that compensates for the result of scanning the radiation pattern is as follows.

When interference arrives at the input of the adaptive antenna array, which compensates for the result of scanning the radiation pattern, at the output of the elements of the antenna array 1, additional phase incursions appear during the scanning of the radiation pattern when calculating the correlation matrix of interference R _xx . The adaptive processor 3, using the known radiation pattern scanning parameters, generates control signals for the elements 5, in which phase incursions occurring during the radiation pattern scanning are compensated. As a result of this, the phase raids are eliminated. This leads to the fact that the correlation interference matrix R _{xx is} calculated taking into account the compensation of the negative influence of the radiation pattern scan, which allows you to form a dip in the radiation pattern to zero, as in the static case.

Achieving a dip to a zero value in the radiation pattern is ensured by the fact that at each time point in the averaging interval, the appearing phase incursion is compensated using the corresponding elements 5. The graphic illustration of the adaptive antenna array compensating for the result of scanning the radiation pattern, in this case, coincides with the graphs given figure 3.

In this situation, with a scanning radiation pattern, the dip level in the direction to the interference source in the radiation pattern is the same as in the radiation pattern in the absence of scanning.

Let us conduct an analytical analysis of the results obtained using the example (m, n) of an element of the interference correlation matrix R _xx . Under the conditions of scanning the radiation pattern for an adaptive antenna array that compensates for the result of scanning the radiation pattern on the averaging interval, (m, n), the element of the interference correlation matrix R _xx will have the form in accordance with formula (2)

- значение компенсационного множителя для помехи, принятой m-м элементом антенной решетки 1 в момент времени t_i;Where

- the value of the compensation factor for the interference received by the m-th element of the antenna array 1 at time t _i ;

- значение компенсационного множителя для помехи, принятой n-м элементом антенной решетки 1 в момент времени t_i.

- the value of the compensation factor for the interference received by the nth element of the antenna array 1 at time t _i .

The remaining designations coincide with the designations disclosed after formula (3).

The factors taken out of the sum sign turned out to be independent of the time reference i, i.e. are constants on the averaging interval. The physical meaning of this remark is that the direction of the source of interference for the averaging time interval has not changed and the generated weight coefficients W _opt according to formula (1) will allow creating a dip in the radiation pattern of the adaptive antenna array, which compensates the result of scanning the radiation pattern to zero.

A detailed description of the work of an adaptive antenna array that compensates for the result of scanning the radiation pattern is as follows.

Upon receipt of the electromagnetic field at the input of the adaptive antenna array, compensating for the result of scanning the radiation pattern, from the output of N elements of the antenna array 1, the inputs X of the inputs of N elements of weighting coefficients 2 and inputs (N × D) of elements 5 are received.

The time interval necessary for calculating the interference correlation matrix R _xx in order to further form the weight coefficients W _opt is represented by the set of time samples {t ₁ , t ₂ , ..., t _L }. At time t ₁ c outputs (N × D) of elements 5 D interference vectors X corresponding to D different sources are supplied to separate corresponding (N × D) inputs of adaptive processor 3, in which the correlation matrix R _xx (t ₁ ) is calculated on time t ₁ by the formula (2).

At time t _2, the inputs (N × D) of elements 5 receive an input signal in the form of an interference vector X with a phase incursion caused by scanning the radiation pattern for the time interval t ₂ -t ₁ . In adaptive processor 3, there is information on phase incursions on the set of time samples {t ₁ , t ₂ , ..., t _L }, according to which adaptive processor 3 generates control signals from its (N × D) outputs that arrive at the control inputs ( N × D) elements 5, eliminating phase raids formed by scanning the radiation pattern for the time interval t ₂ -t ₁ . From the output (N × D) of the elements 5, information in the form of voltages is supplied to the corresponding (N × D) inputs of the adaptive processor 3, in which the correlation matrix R _xx (t ₂ ) is calculated at time t ₂ by the formula (2).

Similarly, you can show the work at other points in time.

Thus, as a result of these actions, the correlation matrix is calculated by formula (2), but with the features of applying the compensation shown in formula (5) for one element of the interference correlation matrix R _xx .

Figure 7 shows the dependence of the energy utilization coefficient on the angular parameter according to the results of modeling the work of an adaptive antenna array that compensates for the result of scanning the radiation pattern. On the ordinate axis, the energy utilization coefficient, measured in dB, is indicated by K _uΔ , dB. On the abscissa axis, the letter u denotes the dimensionless angular parameter. The angular displacements caused by scanning the radiation pattern are indicated: Δu = -0.01 and Δu = -0.001. The curves indicated by the number 1 correspond to the effects of interference exceeding the intrinsic noise by 20 dB, the number 2 by 30 dB, the number 3 by 40 dB and the number 4 by 50 dB.

The simulation results prove that an increase in the angular mismatch caused by scanning the radiation pattern, all other things being equal, does not impair the effectiveness of spatial interference suppression. For example, for interference characterized by a level of 20 dB, which corresponds to the curve indicated by the number 1, the decrease in the spatial suppression efficiency with a mismatch Δu = -0.001 and with a mismatch Δu = -0.01 does not exceed 1.5 dB, which is significantly less than in the case considered in figure 5.

Literature

1. Mozingo MA, Miller T.U. Adaptive antenna arrays. Introduction to the theory. - M., Radio and Communications, 1986.

2. Sheshniak S.S., Popov M.P. Adaptive Antennas. - SPb .: LOVIKA them. A.F. Mozhaysky, 1995.

3. S.M. Rytov, Yu.A. Kravtsov, V.I. Tatarsky. Introduction to statistical radiophysics. Part 1. Random processes. - M.: Science, 1978.

4. Radio-electronic systems. Fundamentals of construction and theory. Handbook / Ed. J.D. Shirman. - M.: MAKVIS CJSC, 1998.

5. Almazov VB, Manzhos VN Receiving and processing of radar information. - Kharkov: VIRTA air defense, 1985.

Claims (1)

An adaptive antenna array that compensates for the scan result, the input of which is N elements of the antenna array, each of whose outputs is connected to the corresponding elements of the weight coefficients, and each of the controlled inputs of the elements of the weight coefficients is connected to the corresponding output of the adaptive processor that generates the weight coefficients, which provide the formation in the diagram the directionality of the dip to a zero value in the direction of the interference source, and the outputs of the elements of the weight coefficients are are the corresponding inputs of the adder, which is the output of the device, characterized in that in addition to the output of the elements of the antenna array are connected (N × D) elements of weighting coefficients of compensation of the results of scanning the radiation pattern, where D is the number of possible interference sources, and for each of the controlled inputs of these elements the corresponding outputs of the adaptive processor are connected, and each of the outputs of the elements of the weight coefficients of compensation of the results of scanning the radiation pattern nen with respective inputs of the adaptive processor which also forms the control signals for the elements of the weight compensation coefficients scan results of the radiation pattern in which the offset phase shifts arising during the scanning of the radiation pattern.

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