RU2451948C1 - Method of calibrating mobile shortwave direction finder with multielement antenna array - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention can be used to calibrate radio signal source direction finders, particularly mobile shortwave (SW) direction finders with a multielement antenna array (AA). The method involves measuring the required number of positions of the radiator for control measurements, the distance between the position of the control radiator (CR) and the closest antenna component (AC) and the coordinate of the positions for installing the CR; receiving a control signal for an N-element distributed AA; frequency selection and measurement of the phase of the received signal pulses; selection of a reference AC, after which CR are successively installed at each given position; determining the initial disparity of measurements of phase difference between each (N-1)-th and the reference AC; and the mean-square deviation (MSD) of the measurement results is calculated; through successive iterations, adjustments are made to the estimate of true coordinates of the AC and the estimated phase defects of feeders and the disparity of phase difference between each (N-1)-th and the reference AC for each position of the CR is re-determined, thereby achieving the minimum attainable MSD of measurement results; and the coordinate values of phase centres of the AC and allowable values of phase offset of the AA feeders, needed for measuring bearings, with minimum error, to signal sources monitored by the mobile direction finder, are determined.

EFFECT: high accuracy of calibrating a mobile shortwave direction finder with a multielement antenna array.

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Description

The invention relates to radio engineering and can be used to calibrate direction finders for radio signal sources, in particular for calibrating short-wave (HF) mobile direction finders with a multi-element antenna array.

Improving the accuracy of modern direction finders is achieved through the use of distributed antenna arrays (AR) with a large number of antenna elements (AE), in particular, sparse ARs placed in a given geometric configuration [1, 2]. However, in the HF band it is practically impossible to create conditions for the deployment of mobile direction finders with a multi-element (N-element) distributed AR, providing the necessary accuracy of the installation of phase centers of the AE and the balance of the channels (feeders) due to the imperfect surface specified for the deployment area, thereby reducing the direction finding accuracy .

The required efficiency of the HF mobile direction finder is controlled and ensured by special calibration [3].

A known method of calibrating direction finder HF range [4, p.570], including the reception of control signals of radio stations with known coordinates, frequency selection and phase measurement of received packages. The known method allows to control the operability of the direction finder, but provides low calibration accuracy and a large value of the mean square [5, p. 280] direction finding error. This is due to the lack of the required number of control emitters (CI) during direction finding from various directions, which does not allow taking measures to reduce direction finding errors.

When implementing the known method there is no possibility of analyzing the reasons for the decrease in calibration accuracy when deploying a mobile direction finder.

The closest in technical essence to the claimed object is a method of calibrating direction finders HF range with multi-element AR, the essence of which is described in [3, p.217-220] (prototype).

The known method includes determining the required number of positions of the emitter for control measurements, the distance between the position of the CI and the closest AE and the position coordinates for installing the CI, receiving a control signal on an N-element distributed AR, frequency selection and phase measurement of the received signal packets. Direction finder calibration is carried out by flying an aircraft (airplane) from the aircraft on board along the route around which the AR is located, with the intersection of pre-selected landmarks. Accuracy of approaches must be at least 1 °. Bearing error is calculated as the difference between the true and the average bearing.

The known method allows you to calibrate a mobile direction finder HF range and evaluate the bearing error, however, the accuracy of calibration is limited.

This is explained by the fact that during calibration, the AR is considered as a static system that does not take into account the installation errors of each AE and the phase imbalance of each AR feeder.

The aim of the invention is to improve the accuracy of direction finding of radio sources by improving the accuracy of calibration of the mobile direction finder HF range with multi-element AR.

This goal is achieved due to the fact that in the known method of calibrating a mobile direction finder HF range with a multi-element AR, which includes determining the required number of emitter positions for control measurements, the distance between the CI position and the closest AE and position coordinates for setting the CI, receiving a control signal at N -element distributed AR, frequency selection and phase measurement of the received signal packages, select the reference AE, after which the KI is sequentially placed in each given position, produce determination of the initial residual [6] of the measurement of the phase differences between each (N-1) and the reference AE and calculate the mean square deviation (RMS) of the measurement results, by sequential iterations introduce corrections in the estimate of the true coordinates of the AE and the estimated defects of the feeder phases and re-determine the residuals measuring the phase differences between each (N-1) and the reference AE for each position of the CI, achieving the minimum attainable standard deviation of the measurement results, and determine the coordinates of the phase centers of the AE and the acceptable values of call imbalance of AR feeders, necessary for measuring with a minimum error of bearings to signal sources controlled by a mobile direction finder.

The proposed method can significantly improve the accuracy of the calibration by introducing amendments that take into account the deployment errors of all AE antenna arrays and defects of the feeders of the antenna system.

The combination of distinguishing features and properties of the proposed method for calibrating a mobile HF range direction finder with a multi-element distributed AR is not known from the literature, therefore, the method meets the criteria of novelty and inventive step.

Figure 1 shows a functional diagram of a variant of a device for calibrating a mobile direction finder HF range.

A device for calibrating a HF mobile direction finder contains a residual calculator 1 and a standard deviation, a control unit 2, a correction input unit 3, a recorder 4 with an indication of the received data and a fully accessible switch 5, the signal outputs of which are connected through the calculator 1 to the input of a recorder 4 with an indication of the received data, and the control input receives a signal from the first output of the control unit 2, the second output of which is connected to the first control input of the residual computer 1 and the standard deviation and is connected to the second input through the correction input unit 3 calculator 1 and RMS residuals, wherein the signal inputs of the switch 5 are fully accessible input device for calibrating a mobile direction finder HF.

A method of calibrating a mobile direction finder HF range with a multi-element AR is implemented as follows.

It is known [3, p. 217] that it is practically impossible for HF range direction finders to provide an ideally even area necessary for deploying an antenna system that corresponds to the AR geometry and provides the necessary accuracy of the AE phase centers installation and channel balance (feeders). And if the design of stationary direction finders, the necessary requirements are taken into account when preparing the deployment site, then in the case of using mobile direction finders of the HF range with N-element distributed ARs, such possibilities are absent.

It is also known [2] that the use of sparse ARs whose distance between neighboring AEs exceeds the value λ / 2, where λ is the wavelength of the received signal, can lead to ambiguity in the phase measurements of signal transmissions and, accordingly, to direction finding errors.

Calibration of the KB range mobile direction finder with an N-element distributed AR allows minimizing the standard deviation. But if the calibration is carried out by the prototype method [3], then the AR is considered as a static system, errors introduced by inaccuracies in the installation of each AE and each feeder are not taken into account.

When using the proposed method for calibrating a KB range finder with an N-element distributed AR, the functioning algorithm is carried out in the following order.

- Determine the required number of emitter positions for control measurements in accordance with the formula M≥ (3N-4) / (N-3), set the distance between the KI and the closest AE in the range R = 10λ ÷ 15λ, set the coordinates of the positions for setting the KI and choose a reference AE.

- The CIs are sequentially placed in each given position, the initial discrepancy of measurements of the phase differences between each (N-1) and the reference AE is determined, and the RMS results are calculated from the results.

where N _AND is the number of measurements;

σ is the discrepancy of measurements;

- среднее значение невязки измерений.

- the average value of the measurement error.

- Through successive iterations, corrections are introduced into the estimate of the true values of the AE coordinates and the estimated phase defects of the feeders, and the residuals of measurements of the phase differences between each (N-1) and reference AE for each position of the CI are re-determined, achieving the minimum attainable standard deviation, and the coordinates are determined phase centers of the AE and the values of the phase imbalance of the AR feeders, which are necessary for measuring with a minimum error of bearings to signal sources controlled by a mobile direction finder.

From a mathematical position, the problem reduces to solving a system of (N-1) · M non-linear equations for measuring a spherical phase front of an electromagnetic wave of the form

φ _ij = ρ _i -k (d _ij -d _0j ) + ε _ij , i = 1, ..., N-1, j = 1, ..., M,

,

,

where φ _ij is the measured phase at the i-th AE relative to the phase of the reference (0th)

AE in the jth dimension;

k is the wave number, k = 2π / λ;

d _ij is the distance from the i-th AE to the j-th position of the CI;

x _i - two-dimensional coordinates of the i-th AE;

y _j - two-dimensional coordinates of the jth position of the CI;

ε _ij is the error of phase measurements;

ρ = {ρ _i }, i = 1, ..., N-1 - estimated defects of the feeder phases;

x = {x _i }, i = 1, ..., N-1 - specified coordinates of AE;

y = {y _j }, j = 1, ..., M are the coordinates of the CI positions.

In the vector form, φ = f (ρ, x, y) + ε or φ = f (z) + ε, where z = {ρ, x, y} (1)

The unknown parameters include: (N-1) phase imbalance elements, (2N-3) refined elements of the AE coordinate vector, 2M elements of the CI coordinate vector, total (3N + 2M-4) unknown parameters.

The solution of the overdetermined nonlinear system (1) can be determined iteratively according to Newton [7, p.653]:

At each step of the iteration, a linearized system is solved

,

,

Where

i = 1, ..., N-1, j = 1, ..., M.

The proposed method can be implemented using a device for calibrating a mobile direction finder HF range, a functional diagram of a variant of which is shown in figure 1.

The signals from the outputs of each phasemeter channel of the direction finder during calibration are fed to a fully accessible switch 5 and then to the residual computer 1 and the standard deviation. The fully accessible switch 5 acts on the commands received from the first output of the control unit 2, and provide the connection of any input to any of the two signal outputs.

The control of the calculator 1 is carried out using control commands supplied through the signal bus from the second output of the control unit 2. Corrections during iterative measurements are introduced into the calculator 1 from the output of the correction input unit 3, which is controlled by the control unit 2 through the signal bus of the second output.

As a fully accessible switch 5, for example, an analog of the PDK-32/64 TMBD 468643.001 device developed by OAO NPK TRISTAN, which has an independent “any to any” switching formula, can be used.

Devices 1-3 can be performed, for example, on the basis of the Texas Instruments TMS 320C 6416/6713 digital signal processor, FPGA [8] and the 2 Xeon Quad processor 2.33 GHz, RAM - 2 GB.

An experimental verification of the proposed method for calibrating the HF mobile direction finder was carried out using a direction finder with an eight-element AR from 18 spaced positions at a frequency of 25 MHz. During the computational process, a system of 136 nonlinear equations with 56 unknowns was solved. In the course of preliminary measurements, the standard deviation was determined = 13.77. As a result of calibration, with a measurement error of 0.01-0.02 degrees, the standard deviation was obtained = 1.61, i.e. the standard deviation was 8.55 times lower, the maximum AE coordinate correction was 37 cm, and the corrected phase imbalance of the feeders was up to 7 degrees. Experimental studies have shown resistance to the choice of the initial approximation and to phase measurement errors, as well as a high convergence rate of no more than 3-5 iterations.

A positive feature of the proposed method for calibrating a mobile HF range finder is the possibility of its use not only for the case of ARs having a configuration in the form of a set of a different number of rings [1], but also for ARs of any other geometric configuration.

Thus, modeling and experimental verification showed that the use of the proposed method allows several times to increase the accuracy of the direction finder HF range with multi-element AR.

Information sources

1. A.D. Vinogradov. Optimization of structures of low-element ring antenna arrays of interferometric direction finders. “Antennas”, issue 1 (42), 1999, pp. 12-14.

2. A.V. Dubrovin. The potential accuracy of direction finding by complexes with antenna arrays having a configuration in the form of a set of an arbitrary number of rings. Radio Engineering and Electronics, 2006, Volume 51, No. 3, pp. 268-270.

3. V.A. Vartanesyan, E.Sh. Goikhman, M.I. Rogatkin. Direction finding. Military Publishing House of the USSR Ministry of Defense, Moscow, 1966.

4. I.S. Kukes, M.E. Starik. Fundamentals of direction finding. "Soviet Radio", Moscow, 1964.

5. B.R. Levin. Theoretical foundations of statistical radio engineering. The second book. Publishing house "Soviet Radio". Moscow, 1968.

6. Mathematical Encyclopedic Dictionary. Moscow, "Soviet Encyclopedia", 1988.

7. G. Korn and T. Korn. Math reference book for scientists and engineers. Ed. "Science", Moscow, 1972.

8. Potekhin D.S., Tarasov I.E. Development of FPGA-based digital signal processing systems. - M .; Hotline - Telecom, 2007.

Claims (1)

A method for calibrating a short-wave direction finder with a multi-element antenna array, which includes determining the required number of emitter positions for control measurements, the distance between the position of the control emitter and the closest antenna element and the position coordinates for installing the control emitter, receiving a control signal on an N-element distributed antenna array, frequency selection and phase measurement of the received signal packages, characterized in that they select the reference antenna element, after h the control radiator is placed in succession at each given position, the initial discrepancy of measurements of the phase differences between each (N-1) and the reference antenna element is determined, and the mean square deviation of the measurement results is calculated, and corrections are introduced into the estimate of the true values of the coordinates of the antenna elements and the estimated defects of the feeder phases and re-determine the residuals of measurements of phase differences between each (N-1) and the reference antenna element for each position of the contact ol emitter, achieving the minimum attainable value of the standard deviation of measurement results, and determining coordinate values of the phase centers of the antenna elements and phase unbalance allowable value of the feeder of the antenna array, required for the measurement with minimum error bearings mobile direction finder for controlled signal sources.

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