RU2366044C1 - Method of shaping adaptive antenna array directional pattern - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: proposed method comprises converting analog RF-signals received by antenna array components into signals suitable for sampling, converting the said analog signals into digital form, setting preset directions of directional pattern lobes, preliminary computation of weight factors (WF) related to each preset lobe direction, storing preliminary computed data in data bank and using optimised WF data for constructing operating directional pattern. Proposed method additionally comprise computing reference directional pattern proceeding from pre-computed WF retrieved from data bank, norming aforesaid reference directional pattern for maxima, computing the pattern with the help of signals received by antenna array components, norming the pattern for maximum and computing the difference vector for aforesaid patterns. Note here that, in digital optimisation of WF, absolute magnitude of aforesaid difference vector is minimised.

EFFECT: suppression of interferences concentrated at pattern angles, including those comparable to useful signal level, without using pilot signals.

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Description

The invention relates to radio engineering and is intended, in particular, for forming a radiation pattern of a short-wave receiving adaptive antenna array.

A known method of orienting an adaptive antenna array, which includes establishing a given direction of the beam pattern, calculating the weight coefficients associated with a given direction of the beam, and the calculation of these weights is independent of the properties of the received signal and interference, and using the calculated weights for forming the pattern [one].

This method does not require the use of a pilot signal, but it does not suppress interference concentrated at the arrival angles if these interference fall within the main or side lobes of the radiation pattern. Adaptation by this method consists only in changing the orientation of the antenna array.

There is a method of forming a radiation pattern of an adaptive antenna array, which includes converting the received radio frequency elements of the analog RF signals into a form convenient for sampling, converting these analog signals to a digital form, numerically optimizing the weight coefficients and using optimized weight coefficients to form a working radiation pattern [2 , 3].

The methods described in [2, 3] make it possible to suppress interference concentrated at the arrival angles, but for this they require a pilot signal.

Closest to the invention in terms of essential features is the method described in [4]. This method of forming the radiation pattern of an adaptive antenna array includes converting the received radio frequency elements of the analog RF signals into a form convenient for sampling, converting these analog signals to a digital form, setting the given directions of the radiation patterns, preliminary calculation of the weight coefficients associated with each given direction beam, and preliminary calculation of these weights is independent of the properties of the received signal and interference, storing pre-calculated weight coefficients in the data bank, numerical optimization of weight coefficients (which in this case is carried out by enumeration of sets of weight coefficients) and the use of optimized weight coefficients to form a working radiation pattern.

In [4], it was reported that in the process of numerical optimization of the weight coefficients, either the maximum signal-to-noise ratio or the maximum of the received signal power together with the interference can be achieved. In the first case, a pilot signal is needed, which can be understood as any information transmitted along with a useful signal, making it possible to distinguish it from interference: somehow a group of bits in a code sequence, a subcarrier, etc. Using a pilot signal for adaptation is undesirable: it needs to be organized, not every possible correspondent has it, it takes energy, etc. In the second case, it is possible to lose contact with the correspondent due to the presence of concentrated interference that exceeds the level of the useful signal: in this case, the radiation pattern of the antenna array is tuned to the direction of the interference [5].

The objective of the invention is to provide a method of forming a radiation pattern of an adaptive antenna array, which allows to suppress noise concentrated at the arrival angles, including those comparable in level with a useful signal and exceeding it, without using a pilot signal.

This technical result is achieved by the fact that in a known method of forming a radiation pattern of an adaptive antenna array, which includes converting the received radio frequency elements of the analog radio frequency signals into a form convenient for sampling, converting these analog signals into digital form, establishing predetermined directions of the radiation patterns, preliminary calculation of weighting factors associated with each given direction of the beam, and preliminary calculation of these weights of the coefficients does not depend on the properties of the received signal and interference, storing pre-calculated weighting coefficients in the data bank, numerical optimization of weighting coefficients and using optimized weighting coefficients to generate a working radiation pattern; additional operations are introduced for calculating the reference radiation pattern from previously calculated weighting coefficients taken from the bank data, normalization of the reference radiation pattern to the maximum, calculation of the pattern vlennosti of signals received by the antenna array elements, its valuation to maximum difference vector calculating directivity patterns of these, and in the process of numerical optimization weighting coefficients minimizing the absolute value of said vector difference patterns.

The ability to achieve the above technical result when using the proposed method was established during a series of numerical experiments.

Figure 1 shows a block diagram of an adaptive antenna array, explaining the inventive method.

Figure 2 shows the original radiation patterns (before optimization), built on the values of the currents in the elements of the antenna array, induced signal and noise.

Figure 3 shows the radiation patterns after optimization, built on the values of the currents in the elements of the antenna array, induced signal and interference.

Figure 4 shows the operational radiation patterns of an adaptive antenna array. Reference patterns are also shown in each of Figures 2-4.

The proposed method is illustrated by the block diagram of the adaptive antenna array shown in figure 1, where it is indicated: 1 - elements of the antenna array, 2 - signal converters in a form convenient for sampling, 3 - analog-to-digital converters (ADC), 4 - control computer, 5 - the processor of the control computer 4, 6 - data bank (a portion of the memory of the control computer 4 allocated for storing information about weight coefficients), 7 - digital-to-analog converter (DAC). The signals received by elements 1 of the adaptive antenna array enter blocks 2, where frequency conversion, noise filtering, the frequencies of which are outside the signal frequency band, and demodulation are performed. Next, in the ADC (blocks 3), the signals are converted to digital form, after which they are sent to the control computer 4, in the processor 5 of which the signals are processed, for which the complex weight coefficients previously calculated for the given direction and frequency are stored in the data bank ( block 6). During processing, weights are optimized to obtain the minimum difference between the reference and the working normalized radiation patterns. Then, in the processor 5, the amplitudes of the signals from the lattice elements are multiplied by the amplitudes of the corresponding optimized weight coefficients, and their phases are added to the phases of the corresponding weight coefficients, i.e. multiply the complex signals from the lattice elements by the corresponding complex weights. After this, a summation of the obtained values is performed, and the total signal is converted into an analog form in the DAC (block 7).

The optimization of weights is as follows. A reference radiation pattern is calculated under the assumption that the signals in the grating elements correspond to the incidence of a plane wave on them from a given direction and a given frequency using a set of weighting factors from a data bank for the same direction and frequency. Normalize this radiation pattern to a maximum in accordance with the expression:

where F (θ, φ) is the normalized radiation pattern for the polar angle θ and azimuth φ;

F _max - the maximum value of the radiation pattern;

n is the number of elements of the antenna array;

F _i (θ, φ) - radiation pattern of the i-th element;

- весовой коэффициент, соответствующий i-му элементу;

- weight coefficient corresponding to the i-th element;

- амплитуда сигнала на i-м элементе;

- the amplitude of the signal on the i-th element;

k is the wave number, k = 2π / λ, where λ is the wavelength;

- радиус-вектор i-го элемента с координатами x, y, z;

- radius vector of the i-th element with coordinates x, y, z;

- орт в направлении θ, φ;

- unit vector in the direction θ, φ;

- коэффициент отражения Френеля для параметров почвы в месте расположения антенной решетки.

- Fresnel reflection coefficient for soil parameters at the location of the antenna array.

Complex quantities are indicated by a dot.

Take a count of signals (digitized) from the lattice elements averaged over time to eliminate the effects of fast fading and modulation of the signal and interference. The radiation pattern is calculated from the mentioned samples of signals and the current value of the weight coefficients. Normalize it to the maximum. By varying the current values of the weight coefficients, the absolute value of the difference vector of the difference of the reference and current radiation patterns is reduced. When the desired magnitude of the vector of the difference of the radiation patterns is reached, the optimization process is stopped, the corresponding value of the current radiation pattern is considered a working radiation pattern, and the corresponding set of weighting factors is considered to be a working radiation pattern and it is used to process a useful signal. The optimization process is repeated at a given time interval or in case of violation of the channel quality characteristics. As initial values for optimization, we take the values of the weight coefficients of the reference radiation pattern.

In a specific example of the proposed method, weighting coefficients are optimized using the UNLSF optimization routine from the IMSL package of scientific routines that are supplied with the modern Fortran translator [6]. The IMSL subroutine solves the nonlinear least squares problem using the modified Levenberg-Marquard algorithm and the finite-difference Jacobian. As an objective function, an m-dimensional vector is used, made up of the difference modules of the normalized radiation patterns — the reference one and calculated from the signals received by the antenna array elements for each of the m radiation pattern points.

The data bank stores sets of weighting coefficients previously calculated for all frequencies and directions provided by the wave schedule of the radio station. In the preliminary calculation process, the weight coefficients can also be optimized to increase the coefficient of directional action (narrowing radiation patterns due to the use of superdirectionality) and to compensate for errors caused by inaccuracies in the manufacture and installation of the antenna array, the influence of which can be significant when using superdirectionality.

The possibility of suppressing interference concentrated at the arrival angles with a level comparable to and exceeding the level of the useful signal without using a pilot signal while minimizing the difference between the reference and working radiation patterns was identified and confirmed during a series of numerical experiments. In figures 2-4 presents the radiation patterns constructed for the antenna array in the form of a circular ring with a radius of 8 m, formed by six elements operating at a frequency of 3 MHz. The lattice elements are symmetrical vertical vibrators 2 m long with a suspension height of the center of the vibrator above the ground 3 m. Earth parameters: relative dielectric constant 10, specific conductivity 0.01 C / m. Preset direction: zero azimuth, polar angle θ = 70 °. In all three figures, the azimuthal radiation pattern corresponds to the polar angle θ = 70 °, the radiation pattern in the vertical plane corresponds to the zero azimuth φ = 0. Curves 3 and 4 in all three figures are reference radiation patterns: 3 - azimuthal, 4 - in the vertical plane. The part of the reference vertical radiation pattern corresponding to θ> 90 ° is shown as specular reflection. Reference radiation patterns are optimized during the preliminary calculation of weighting coefficients in order to increase the directivity coefficient due to overdirectionality. In Fig. 2, curves 1 (azimuthal radiation pattern) and 2 (radiation pattern in the vertical plane) are plotted for two signals of equal amplitudes and phases coming from a given direction φ = 0, θ = 70 ° and from the direction θ = 70 °, φ = 50 °, which is considered the direction of arrival of the interference, before adaptation (i.e., before optimization, aimed at reducing the difference vector of the current and reference radiation patterns). In Fig. 3, the same curves 1 and 2 depict radiation patterns calculated in the same way, i.e. according to the signals received from two sources, after adaptation. It can be seen that the azimuthal radiation pattern substantially approached the reference one. Figure 4 shows the radiation patterns, calculated, as in figure 3, by optimized weighting coefficients, but by signals from only one source working from a given direction; thus, these are true directivity patterns: these would be exactly what would happen if the signal source moves around the antenna - just as the directivity pattern of receiving short-wave antennas is measured by flying around. Indeed, when a plane wave is incident from a given direction, the corresponding signals will be induced on the lattice elements. Further, these signals are multiplied by weights and summed. If you reverse the direction of the signal, we get the following. The signals from the transmitter are divided into n parts, multiplied by weights and fed to the antenna elements, where they are emitted. Based on the principle of reciprocity, this will be the same radiation pattern as in the receiving version. The azimuthal radiation pattern has a deep dip in the direction close to φ = 50 °, i.e. the interference is significantly suppressed (the exact value of the suppression is 21.36 dB relative to the signal from a given direction; the signal in a given direction is 0.8888 from the maximum, since the maximum has shifted somewhat). The signal and the interference did not differ from each other either in frequency, or in level, or in phase, or in any other characteristic that could be counted as the presence of a pilot signal.

Adaptation using the reference radiation pattern takes longer than with the pilot signal, but for the short-wave range this, as a rule, is not significant, because interference in this range usually changes slowly.

Used sources

1. RF patent No. 2216829, IPC ⁷ H01Q 3/26.

2. RF patent No. 2232485, IPC ⁷ H04Q 7/30.

3. RF patent No. 2287880, IPC H01Q 21/29 (2006.01), H01Q 3/26 (2006.01).

4. US patent No. 7312750, IPC H01Q 3/22 (2006.01), H01Q 3/26 (2006.01).

5. Active phased antenna arrays / Ed. D.I. Voskresensky and A.I. Kanaschenkov. - M.: Radio Engineering, 2004 .-- 488 p.

6. Bartenev OV FORTRAN FOR PROFESSIONALS. IMSL Mathematical Library: Part 2. - M .: DIALOGUE-MEPhI, 2001 .-- 320 p.

Claims (1)

A method of forming a radiation pattern of an adaptive antenna array, which includes converting the received radio frequency elements of the analog RF signals into a form convenient for sampling, converting these analog signals to a digital form, setting the given directions of the radiation patterns, preliminary calculation of the weight coefficients associated with each given direction beam, and preliminary calculation of these weights is independent of the properties of the received signal and omech, storing pre-computed weights in the data bank, numerical optimization of weights, using optimized weights to form a working radiation pattern, characterized in that the pre-calculated weights taken from the data bank calculate the reference radiation pattern, normalize it to the maximum , calculate the radiation pattern according to the signals received by the elements of the antenna array, normalize it to the maximum, calculate the vector differently These radiation patterns, and in the process of numerical optimization of weighting coefficients, minimize the absolute value of the aforementioned vector of the difference of radiation patterns.

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