RU2790956C2 - Method for calibration of magnetic frame antennas - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: invention relates to the field of radio engineering, specifically to means for metrological provision of magnetic field strength meters; it can be used in calibration of magnetic frame antennas. The use of three magnetic frame antennas for conducting a series of three measurements is described. In each of measurements, one of antennas is transmitting and is connected to a measuring generator, and the second antenna is receiving and is connected to an input of a measuring receiver. Based on strength measurement results obtained using the measuring receiver from an output of each of antennas used as receiving, calibration coefficients of each of three calibrated antennas are calculated.

EFFECT: increase in the accuracy of calibration, expansion of a frequency calibration range, expansion of the range of types of calibrated magnetic frame antennas.

1 cl, 3 dwg

Description

The present invention relates to the field of radio engineering, and specifically to the means of metrological support for magnetic field strength meters, and can be used in the calibration of magnetic loop antennas.

A known method of calibrating magnetic antennas in the frequency range from 10 Hz to 30 MHz, which consists in excitation by a loop antenna of a uniform magnetic field, the strength of which is calculated from the magnitude of the current flowing in the radiating frame and its design parameters, measuring the strength of the generated magnetic field using a calibrated antenna [1] and determining the calibration coefficients by the calculation method [2].

The disadvantages of this method are:

low structural reliability of the field-forming system;

the need to create a separate measuring line to determine the magnitude of the current in the radiating antenna;

the need for large areas to accommodate the installation.

A known method for calibrating magnetic antennas in the frequency range from 10 Hz to 30 MHz, which consists in creating a uniform magnetic field with a known strength in a limited area of space using an installation based on Helmholtz rings, measuring the strength of the generated magnetic field using a calibrated antenna and determining the calibration coefficients by the calculated method. [3]

The disadvantages of this method are:

dependence of the frequency range of the installation on its geometric dimensions;

small size of the working area of the installation.

These shortcomings lead to a decrease in the calibration accuracy of magnetic loop antennas, a limited range of types of calibrated magnetic loop antennas, and an increase in the cost of creating, maintaining and operating installations.

There is a method for calibrating magnetic loop antennas based on the substitution method. The method consists in excitation of an electromagnetic field by a transmitting auxiliary loop antenna in the plane of a reference antenna with known characteristics, measuring the voltage from the output of the reference antenna using a spectrum analyzer (measuring receiver), excitation of an electromagnetic field by a transmitting auxiliary loop antenna of the same magnitude in the plane of the antenna being calibrated, measuring the voltage from the output of the calibrated antenna using a spectrum analyzer (measuring receiver) and calculating the calibration coefficients of the calibrated antenna based on the measured voltage values from the output of the reference and calibrated antennas and the known calibration coefficients of the reference antenna. [4]

The disadvantages of the known method are:

the need for a reference antenna with known calibration factors;

limitation of the potentially achievable calibration error by the error in determining the calibration coefficient of the exemplary antenna;

the frequency range of the reference antenna must overlap the frequency range of the antenna being calibrated.

These shortcomings lead to a decrease in the calibration accuracy of magnetic loop antennas and an increase in calibration costs.

This method is closest to the proposed invention and is selected as a prototype.

The purpose of the invention is to increase the accuracy of calibration of magnetic loop antennas, to expand the frequency range of calibration of magnetic loop antennas, to expand the range of types of calibrated magnetic loop antennas, as well as to simplify the design, reduce the cost of creating, maintaining and operating promising installations for calibrating magnetic loop antennas implemented on the basis of the proposed method.

The essence of the invention is as follows. The calibration uses three magnetic loop antennas with unknown calibration factors. When conducting a series of three pairwise measurements, the voltage from the output of each of the magnetic loop antennas is sequentially measured and the calibration coefficients for each of the three calibrated antennas are calculated based on the obtained measurement results.

A series of measurements is carried out according to the scheme: 1-2, 1-3, 2-3 - where, at the beginning, the receiving antenna is indicated, and then the emitting one. In this case, the receiving antenna is connected to the spectrum analyzer, and the emitting antenna is connected to the voltage calibrator. The measurements are carried out in the frequency range common to all three antennas.

The proposed method allows measuring the calibration coefficient of both passive and active loop antennas. In this case, only one of the three participating in the measurements can be an active antenna. In the case of measuring the calibration coefficients of an active antenna, it should be designated under the number "1" and work only for receiving a signal from a radiating antenna.

For each measurement, two antennas are located opposite each other coaxially and coaxially, at a height of at least 1.75 ± 0.1 m and at a distance in accordance with the ratio:

, (1)

, (1)

where r - antenna radius, m.

Measurement of the calibration coefficients of each of the three magnetic loop antennas by the proposed method is carried out as follows.

Calibrate the measuring cable.

To do this, the calibrated measuring RF cables 6 and 7 are connected and connected to the input of the spectrum analyzer 4 and to the output of the voltage calibrator 5. Turn on the broadband mode on the calibrator 5 and tune it to the initial measurement frequency from the frequency range of the measured antennas. Then set the voltage from the output of the calibrator 5U _To from the voltage range, depending on the dynamic range of the measured antennas. The recommended voltage value from the output of calibrator 5 is assumed to be 1 V. Tune spectrum analyzer 4 to the frequency of voltage calibrator 5. On spectrum analyzer 4, turn on the software attenuator by 5 dB or more, depending on the valueU _To . In this case, the attenuation value is chosen as a multiple of 5 dB. Measure the magnitude of the signalU _caliber (f ₀ ), Wheref ₀ - initial frequency of the measurement range, MHz. Repeat measurementsU _caliber at all frequency points specified in the regulatory documents for the measured antennas.

Next, measure the voltage from the output of the antennas. For this, a circuit is assembled in accordance with Fig. 1. Install antenna 1 and antenna 2 opposite each other at a distance calculated in accordance with formula (1). In this case, antennas 1 and 2 are installed coaxially, which can be checked using a laser rangefinder. Antenna 1 is connected to the input of the spectrum analyzer 4, and antenna 2 to the output of the voltage calibrator 5. Set the voltage from the output of the calibrator 5, equal toU _To . Tune the spectrum analyzer 4 to the frequency of the voltage calibrator 5. At frequencies above 200 Hz, the spectrum analyzer 4 includes a software attenuator of 5 dB or more, depending on the dynamic range of the measured antennas. In this case, the attenuation value is chosen as a multiple of 5 dB. Measure the magnitude of the signalU ₁₂ (f ₀ ), Wheref ₀ - initial frequency of the measurement range, MHz. Repeat measurementsU ₁₂ at all frequency points specified in the regulatory documents for the measured antennas.

Measurements are carried out in the same way.U ₁₃ (Fig. 2) andU ₂₃ (Fig. 3). In this case, the antennas are placed according to the scheme 1-3, 2-3 (where, at the beginning, the receiving antenna is indicated, and then the emitting antenna), at a distance calculated in accordance with formula (1).

The calibration coefficients of loop antennas No. 1, 2 and 3 are calculated at each frequency point using the equations:

, (2)

, (2)

, (3)

, (3)

, (4)

, (4)

where r ₁ , r ₂ , r ₃ - antenna radii, in accordance with the regulatory and technical documentation, m; d ₁₂ , d ₁₃ , d ₂₃ - distance between antennas, m; a ₁₂ , a ₁₃ , a ₂₃ - coefficients describing the magnetic field of the emitting antenna, averaged over the area of the receiving frame; k - wave number; f - measurement frequency, Hz; μ ₀ - magnetic constant, H/m; Z is the load of the measuring line, Ohm; U ₁₂ , U ₁₃ , U ₂₃ - voltage from the output of the receiving antenna, V.

If necessary, the values of the calibration coefficient of each of the three antennas, determined relative to the magnetic field strength (1/Ohm m) are recalculated into calibration coefficients relative to the electric field strength on a logarithmic scale (dB(m ^-1 )) according to the formula [5]:

, (5)

, (5)

where i is the antenna number.

The novelty of the invention lies in a new approach to the calibration of magnetic loop antennas, based on the fact that the calibrated antennas themselves perform the function of a field-forming system during the calibration process, which makes it possible to calibrate magnetic loop antennas with a priori unknown calibration coefficients.

The inventive level is characterized by the use of three magnetic loop antennas with a priori unknown calibration coefficients for a series of three pairwise measurements, in each of which one of the antennas connected to the voltage calibrator (measuring generator) creates a magnetic field in the plane of the second antenna, which is the receiving and connected to the input of the spectrum analyzer (measuring receiver), with the subsequent calculation of the calibration coefficients of each of the three calibrated antennas based on the results of voltage measurements from the output of each of the antennas used as a receiver.

This invention is industrially applicable in the development of promising installations for the calibration of magnetic loop antennas used in solving the problems of electromagnetic compatibility of aviation radio-electronic equipment, measuring the parameters of the electromagnetic field during research, in radio frequency identification (RFID) systems, wireless data transmission networks, as well as in tasks technical protection of information.

Information sources

1. Buzinov V.S. Installation for verification of frame INP according to the exemplary field of induction / Measuring equipment. 1961. No. 6. pp. 46-48.

2. Greene F.M. The Near-Zone Magnetic Field of a Small Circular-Loop Antenna. JOURNAL OF RESEARCH of National of Bureau of Standards - C. Engineering and Instrumentation, October-December 1967, vol. 71C, no. 4, pp. 319-326.

3. Fano W.G. Standard Electric and Magnetic Field for Calibration. IntechOpen, 2018.

4. Fujii K., Sakai K., Sugiyama T., Sebata K., Nishiyama I. Calibration of Loop Antennas for EMI Measurements in the Frequency Range Below 30 MHz. Journal of the National Institute of Information and Communications Technology 63(1), 2016, pp. 71-81.

5. GOST CISPR 16-1-4-2013. Compatibility of technical means is electromagnetic. Requirements for equipment for measuring the parameters of industrial radio interference and noise immunity and measurement methods. Part 1-4. Equipment for measuring the parameters of industrial radio interference and noise immunity. Antennas and test sites for measuring radiated interference. - M.: Standartinform, 2014.

Claims (1)

A method for calibrating magnetic loop antennas, in which the calibration coefficients of the receiving antenna are determined based on voltage measurements from the output of the receiving magnetic loop antenna when an electromagnetic field is excited by the transmitting magnetic loop antenna, characterized in that three magnetic loop antennas with a priori unknown calibration coefficients are used for calibration. a series of three pairwise measurements, in each of which one of the antennas is transmitting and connected to the measuring generator, and the second antenna is receiving and connected to the input of the measuring receiver, with the subsequent calculation of the calibration coefficients of each of the three calibrated antennas based on those obtained using the measuring receiver results of voltage measurements from the output of each of the antennas used as a receiver.

Images