RU2722409C1 - Two-electrode tem strip line with variable dimensions and tunable load and matching device - Google Patents

Abstract

FIELD: physics.SUBSTANCE: invention can be used for testing objects on action of harmonic electromagnetic fields. Essence of the invention consists in that the two-electrode TEM strip line with variable dimensions, tunable load and matching device, comprising a series-connected transition section with a connector for connecting a signal source, a matching device in the form of an L-shaped resistive four-terminal element, a field-forming system and a load, characterized in that field-forming system has variable geometry and consists of upper and lower wire current conductors and lifting mechanism with dielectric trusses, length and width of plane-parallel part of upper and lower current distributors are not less than 30 percent more than length and width of test object, distance between plane-parallel part of upper and lower current distributor is not less than 2 times greater than height of test object, resistive elements R2 and R3 of the matching device are made in form of a set of switched resistors and their values are determined by corresponding expressions.EFFECT: technical result is enabling use of the disclosed device with one signal source for testing objects of small and medium size for resistance, strength, safety and susceptibility to action of harmonic electromagnetic fields of high intensity and for tests of large-size objects on safety and susceptibility to action of harmonic electromagnetic fields due to change of working volume of TEM strip line, as well as adjustment of load and matching device to dimensions of test object.1 cl, 7 dwg, 1 tbl

Description

The invention relates to electrical engineering and can be used to test objects for resistance, strength, safety and susceptibility to the action of harmonic electromagnetic fields.

Known Technique [Crawford M.L. Generation of standard EM fields using TEM transmission cells // IEEE Transactions on Electromagnetic Compatibility. - 1974. - Vol. EMC-16. - No. 4. - P. 189-195], which describes the propagation of a transverse electromagnetic wave with a given level of electric field strength along a transmission line with the required characteristic resistance at frequencies below the higher modes. Using this technique, a TEM camera was made, which consists of a closed conductor made of a rectangular parallelepiped and two pyramidal parts, at the tops of which connectors are placed to connect the central plate located inside the closed conductor to the generator and to the load with a given resistance. The operating frequency range of the TEM camera is limited by the first resonant frequency, which is necessary for the uniform propagation of electromagnetic fields (EMF) in the internal volume of the TEM camera. The disadvantage of this device is the small working volume and the impossibility of increasing it.

From the patent RU 2606173 C1, Н01Р 1/00, December 28, 2015, a TEM camera is known for testing objects for electromagnetic compatibility (EMC) and studying the effects of electromagnetic fields on biological objects, and containing a body with a central part in the form of a rectangular parallelepiped of four conductive surfaces, on the open ends of which there are two tapering parts in the form of pyramids, the vertices of which are connected to the connector body, the central conductor of which is connected to a central plate located in the inner cavity of the body. The optimal shape and dimensions of the case and the central plate of the TEM camera provide an increase in the operating frequency up to 1-2 GHz with a maximum height of the test object of 40 mm and a maximum coefficient of standing waves with a voltage not exceeding 1.08. The disadvantage of this device is the small working volume and the impossibility of increasing it.

From the patent EP 1283990 B1, G01R 29/08, 08/08/2011, a TEM camera is known for measuring emissions and testing objects for resistance to electromagnetic fields and containing at least six faces of a conductive material with an opening in one of them. The faces are placed so that they form a closed box with an inlet. The internal volume includes a set of conductors, at least one of which is connected to two connectors and is located in a plane perpendicular to the plane of the test object. The internal volume may also contain elements for mixing electromagnetic radiation, and the conductive structures inside may be coated with radar absorbing material. The disadvantage of this device is the small working volume and the impossibility of increasing it.

From the certificate for utility model RU 36737 U1 G01R 31/00, December 20, 2003, a TEM camera is known for testing technical equipment for resistance to electromagnetic fields and containing a segment of a rectangular waveguide with pyramidal elements adjacent to the ends of a rectangular waveguide at the vertices of which made coaxial conclusions. A hole has been made in the wall of the TEM camera, an extraordinary waveguide is installed on the outer surface of the wall of the TEM camera opposite the hole, and the TEM camera is additionally equipped with a lighting device that includes a light source located outside the TEM camera and an optical fiber, the first end of which is optically connected with a light source, the second end is equipped with a dielectric lens and placed inside the TEM camera, and the middle part passes through the hole and the transcendental waveguide. The disadvantage of this device is the small working volume and the impossibility of increasing it.

From patent RU 2207678 C1 H01Q 17/00, G01R 31/00, 11/19/2001, a TEM camera is known for testing technical means for resistance to electromagnetic fields with a high level of field strength and containing a segment of a rectangular waveguide with pyramidal elements adjacent to the ends a rectangular waveguide, at the vertices of which coaxial leads are made, a high-frequency generator and matching load connected to the coaxial leads. An observation hole is made in the wall of the pyramidal element adjacent to the high-frequency generator. The TEM camera is equipped with a video camera located opposite the inspection hole, the video camera can be enclosed in a shielding casing, paired with the outer surface of the pyramidal element of the TEM camera. The disadvantages of this device include the impossibility of changing the working volume of the TEM camera if it is necessary to test large objects.

From the patent RU 2208774 C2 G01M 17/00, Н05В 6/64, 06/04/2001, a TEM camera is known for testing vehicles for EMC and containing a segment of a rectangular waveguide with pyramidal elements made of electrically conductive material adjacent to the ends of the rectangular waveguide at the vertices of which (pyramidal elements) coaxial connectors are installed, as well as a conductive plate connected to the central contacts of the coaxial connectors, a generator and a matching load connected to the coaxial connectors. The TEM camera is equipped with at least one lighting device located near the lower edge of the rectangular waveguide. This invention is directed to equipping a TEM camera with a stationary light source and providing a uniform electromagnetic field. The disadvantages of this device include the impossibility of changing the working volume of the camera if it is necessary to test large objects.

From patent RU 2103771 C1 H01Q 17/00, G01R 29/08, 01/27/1998, a TEM camera is known for testing EMC electronic devices, for studying the effects of EMFs on living organisms, for calibrating EMF sensors and containing an external pyramidal closed conductor, inside of which, in the immediate vicinity of the base, a combined load is installed made of an absorbing panel of high-frequency absorbers and ohmic resistances, an asymmetrically located inner conductor made of a conductive sheet passing in the load region into a flat plate of smaller width passing through the absorbing panel and connected to ohmic resistances while a coordinated transition is established from the side of the top of the pyramid to connect the signal generator. A design feature is the special shape of the inner conductor, which is made as part of the side surface of the cone with a section radius determined by a predetermined ratio, which makes it possible to improve the uniformity of the main field component by 0.5 ... 1.0 dB, reduce the stray component of the field in the transverse direction of the working chamber volume and reduce test error. The disadvantages of this device include the impossibility of changing the working volume of the camera if it is necessary to test large objects.

From the patent US 5436603, Н01Р 1/00, 3/06, 07.25.1995, a TEM camera is known for testing objects for noise emission and noise immunity and containing a hollow metal casing with two tapering sections. Also, at the ends there is at least one connector, which is connected to a Central plate located in the inner cavity of the metal casing and having a stepped shape to reduce the value of the coefficient of standing waves voltage. The disadvantage of this device is the small working volume and the impossibility of increasing it.

From US Pat. No. 4,659,916 A, H01P 1/00, 3/06, 08/12/1986, a TEM camera is known for testing objects for exposure to electromagnetic radiation and containing an external metal shielding housing having conical surfaces at the opposite ends in the form of a plurality of inclined walls, as well as an internal metal partition in the form of a plate passing along the longitudinal axis of the shielding housing, which at the ends is connected to the generator and the load through the connecting part, and also contains an insulating gasket between the housing and the central conductor of the connector. A particular drawback of the camera is the presence of transitions with mechanical fastening of the internal partition, which causes uneven field propagation at the beginning and end of the TEM camera and a high coefficient of standing waves in voltage, moreover, in the relatively small operating frequency range up to 100 MHz, and the main disadvantage is the small working volume and the impossibility of increasing it.

From the patent RU 2465610 C2 G01R 29/08 08/12/2008 a strip antenna is known for EMC testing, comprising a telescopic type upper and lower plate having parallel longitudinal axes supported at a distance from each other and mechanically connected to each other on longitudinal ends with longitudinal plates. The upper, lower and longitudinal plates are mounted for movement, while the distance between the lower and upper plates can be changed by shifting the female and male parts of the upper and lower plates, respectively.

The disadvantage of this device is the restriction on increasing the size of the antenna imposed by the size of the telescopic elements: firstly, the maximum length of the structure cannot be greater than the sum of the lengths of the female and male parts of the current lead, and secondly, the height of the antenna cannot be greater than the sum of the heights of the triangular elements of the longitudinal plates of the antenna thirdly, the width of the antenna plates is not adjustable and there is no agreement on the changing wave (characteristic) resistance of the structure with a constant output impedance of the signal source and load resistance.

Closest to the claimed device is the TEM strip line described in [Hilavin S., Kustepeli A. Design and Implementation of TEM Stripline for EMC Testing // IEEE Transactions on Electromagnetic Compatibility. - 2014 .-- Vol. 56. - No. 1. - P. 23-27]. The paper shows the procedure for the development, design, calibration and verification of the TEM strip line for testing to assess the sensitivity to radiated electromagnetic fields of audio and video equipment whose size exceeds 70 cm and cannot be tested in standard TEM strip lines. With an increase in the size of the TEM line, the wave (characteristic) resistance of the line changes and the uniformity of the reproduced EMF deteriorates. To reduce the reflections, a matching device is used and a load resistance equal to the wave impedance of the line with fixed resistor values.

The disadvantage of the prototype device is the impossibility of changing the working volume of the TEM strip line and the adjustment of the matching device and the agreed load.

The two-electrode TEM strip line with variable dimensions and tunable load and matching device (hereinafter TEM strip line) includes:

transition section with a coaxial connector for connecting a signal source, with a tunable resistive matching device in the form of a L-shaped resistive four-terminal, with two storage cases for coils with flexible conductors for the upper and lower current conductors, with two metal plates with clamps for fixing the conductors of the upper and lower conductors;

lower conductors of 3 or more flexible conductors laid parallel to the underlying surface at an equal distance from each other and secured on one side with clamps for fixing on the transition section, and on the other, clamps for fixing on the load;

the upper conductor of 3 or more flexible conductors mounted in parallel on dielectric load-bearing trusses at an equal distance from each other and connected on one side to the clamps for fixing on the transition section, and on the other - clamps for fixing to the load;

a lifting mechanism consisting of at least 4 winches designed to lift two or more dielectric farms, to which the flexible conductors of the upper current lead are suspended;

adjustable coordinated load, consisting of a set of switched resistors connected to metal plates with clamps for fixing the conductors of the upper and lower current conductors.

The technical result is the use of the inventive device with a single signal source for testing objects of small and medium sizes for resistance, strength, safety and susceptibility to the action of harmonic electromagnetic fields of high intensity and for testing large objects for safety and susceptibility to the action of harmonic electromagnetic fields by changing the working the volume of the TEM strip line located between the plane-parallel part of the upper and lower current conductors, as well as load adjustment and matching devices to the dimensions of the test object.

The size of the working volume is adjusted to the dimensions of the test object so that the width and length of the working volume exceed the transverse dimensions of the test object by at least 30%, and the height of the working volume is not less than 2 times its height.

This ensures a decrease in the error of the test results by improving the uniformity of the spatial distribution of electromagnetic fields inside the working volume of the TEM strip line by matching the constant resistance of the signal source and the changing wave (characteristic) resistance of the TEM strip line caused by a change in the distance between the upper and lower current conductors or a change in them width.

The technical result is achieved through the use of the upper and lower conductors of the wire structure, which allows you to change the length and width of the conductors, as well as through the use of a lifting device that allows you to change the height of the suspension of the upper conductors, with the resulting mismatch in the output impedance of the signal source and characteristic (wave) resistance compensated by means of an adjustable matching device in the form of a L-shaped resistive four-terminal device and an adjustable coordinated load.

The invention is illustrated by drawings, which do not cover and, moreover, do not limit the entire scope of the claims of this technical solution, but are only illustrative materials of a particular case of execution.

In FIG. 1 shows an isometric view of the claimed device.

In FIG. 2 is an isometric view of the transition section.

In FIG. Figure 3 shows an isometric view of the matched load.

In FIG. 4 shows an electrical equivalent circuit for calculating R2 and R3 of an adjustable matching device in the form of a L-shaped resistive four-terminal device.

In FIG. Figure 5 shows the dependence of the characteristic (wave) resistance of the TEM strip line on the height of the suspension of the upper conductors for the width of the upper and lower conductors 6 m and 11 m

In FIG. Figure 6 shows the dependence of the characteristic (wave) resistance of the TEM strip line with the width of the lower current path 6 m, the width of the upper current path 6 m and the resistances R2 and R3 of the matching device on the height of the suspension of the upper current path for the output resistance of the signal source 50 Ohms.

In FIG. Figure 7 shows an example of measuring the frequency dependence of the standing wave coefficient over voltage when using a matched load and matching device and without them.

In the inventive device (Fig. 1), the lower current lead 1 formed by a system of flexible conductors is laid on the underlying surface. The conductors are, on the one hand, connected to the clamps 5 for fixing on the transition section 3, and on the other hand, to the clamps 6 for fixing on the load 4. The width of the lower current lead is changed if necessary by changing the number of conductors and the distance between them. In this case, the width of the current lead should be greater than the width of the test object by at least 30%.

The upper current lead 2 is formed by a system of flexible conductors that are suspended from the dielectric trusses 9. The conductors are, on the one hand, connected to the clamps 7 for fixing on the transition section 3, and on the other hand, to the clamps 8 for fixing on the load 4. The width of the upper current lead is changed by changing the number conductors and the distance between them. In this case, the width of the current lead should be greater than the width of the test object by at least 30%.

The lifting of the upper current lead 2 to a predetermined height is carried out by a lifting mechanism consisting of at least 4 winches 10 or lifting masts. In this case, the distance between the plane-parallel part of the upper and lower current conductors should be at least 2 times greater than the height of the test object.

The length of the lower and upper conductors is changed by increasing the distance between the transition section 3 and the coordinated load 4 and the supply of conductors wound on coils located in canisters 25 and 26 (Fig. 2), as well as using additional dielectric trusses 9 and winches 10. the length of the conductors must be at least 30% greater than the length of the test object.

The placement of pencil cases 25 and 26 with coils for conductors on the outside of the TEM strip line provides a reduction in electrical heterogeneity and an improvement in the distribution of the electromagnetic field inside the device.

The transition section 3 and the coordinated load 4 are mounted on movable height-adjustable support tables 11 and 12. The support tables are equipped with lifting mechanisms 13 and 14 to change the height of the transition section 3 and the coordinated load 4.

The transition section (Fig. 2) includes a frame 15, on which is located a dielectric plate with a high-frequency coaxial connector 16 for connecting a powerful signal source 32 (Fig. 1). On the reverse side of the connector, a trapezoidal metal plate 17 is connected to its central electrode, on the opposite side of which there is a dielectric insert 18. A set of switchable resistors 19 of the matching device is fixed to the dielectric insert. On the one hand, the resistors are connected to the trapezoidal plate 17, and on the other to a trapezoidal plate 20, on the opposite side of which there are clamps 7 for fixing the flexible conductors of the upper current lead 2. The electrical connection is a set of switched resistors 19 of the matching device correspond to the connection of the resistor R3 on the equivalent circuit FIG. 4.

The outer conductor of the coaxial connector 16 is connected to the trapezoidal metal plate 21. On the opposite side of the plate are clamps 5 for fixing the flexible conductors of the lower current lead 1.

Between the upper 17 and lower 21 plates of the transition section, a dielectric insert 22 is mounted on which a set of switchable resistors 23 of the matching device is fixed. On the one hand, the resistors are connected to the plate 21, and on the other to the plate 17. The electrical connection of the set of switchable resistors 23 of the matching device corresponds to the connection of the resistor R2 in the equivalent circuit in FIG. 4.

Heat removal from the sets of switched resistors 19 and 23 is provided by radiators 24.

On the transitional section 3, on the sides facing the upper 2 and lower 1 conductors of the strip line in the upper and lower parts of the frame 15, there are cases 25 and 26 with coils on which a supply of flexible conductors is wound, forming the lower 1 and upper 2 conductors of the strip line.

Adjustable coordinated load (Fig. 3) includes a frame 27, on which there are two plates 28 and 29 with clamps 6 and 8 for fixing the flexible conductors of the lower 1 and upper 2 current conductors. Between the plates 28 and 29, there is a dielectric insert 30 on which a set of switched resistors 31 is fixed. Resistors are connected to the upper plate 29 on the one hand and to the lower plate 28 on the other. The electrical connection of the switched resistors 31 corresponds to the connection of a matched asymmetrical strip line resistor R4 (Fig. 4).

Heat removal from the resistors is provided by the radiator 24.

The adjustment of the matching device and the coordinated load for the parameters of the wave (characteristic) resistance of the TEM strip line is carried out according to the following algorithm.

For the selected width of the upper and lower conductors, which should be at least 30% more than the width of the test object, and the height of the suspension of the upper conductors, which should be at least 2 times greater than its height, the wave (characteristic) resistance in the transverse the TEM section of the strip line of the wire structure, based on the approximation of the TEM wave, whose electric field at the input of the field-forming system coincides in structure with the stationary electric field of the infinite transmission line with the corresponding cross section. For a given potential difference between the internal and external electrodes of an infinite homogeneous line, the charge distribution over the wires forming the electrodes is found. It is assumed that the wires are quite thin and the surface charge density σ _i (i = 1 ... N) on each of them could be considered constant. Then the electric potential of the jth wire in accordance with the principle of superposition is calculated through the charge density [Harrington RF Field Computation by Moment Method. - Mc'Millan Company, New York, 1968. - 158 p]:

The constants c _ij , called potential coefficients, are found by integration over the surface of the i-th wire S _i :

- расстояние между фиксированной точкой

на оси j-й проволоки и точкой

на поверхности i-й проволоки.Where

- distance between a fixed point

on the axis of the j-th wire and the point

on the surface of the i-th wire.

The integral over the surface is replaced by the integral along the axis of the ith wire:

where a _i is the radius of the i-th wire, ρ _ij is the distance between the axes of the wires (for i ≠ j).

For i = j, in order to avoid the singularity of the integrand, the standard method of the fine-wire approximation is used [Volman VI, Pimenov Yu.V. Technical electrodynamics. - M .: Communication, 1971. - 488]. Instead of ρ _ij in (3), the radius of the wire is substituted.

After calculating the coefficients c _{ij of the} system of linear equations (1) and solving it for a given potential difference U between the electrodes, we obtain the desired charge distribution. Taking into account the fact that the electric and magnetic components of the TEM wave field are connected by the relation H = E / 120π, and on the surfaces of the electrodes they satisfy the boundary conditions [Goldstein L.D., Zernov N.V. Electromagnetic fields and waves. - M .: Soviet Radio, 1971. - 186 p.]

where J is the surface current density,

the total current on one of the electrodes is calculated by the formula

In this case, the wave impedance is determined by the expression

The load resistance TEM of the strip line R4 is taken equal to the wave impedance Z _in .

The approach described above for determining wave (characteristic) resistance is implemented as a software module in Fortran language. An example of the results of calculating the wave resistance depending on the height of the suspension of the upper conductors from 0 to 6 m for the width of the upper and lower conductors 6 m is shown in FIG. 5.

In the event that the wave (characteristic) impedance for the TEM strip line will differ from the wave impedance of the signal source, then for their coordination it is necessary to configure a tunable resistive matching device in the form of a L-shaped resistive four-terminal, made on resistors R2 and R3 according to the scheme, shown in FIG. 4.

The following expressions are used to determine the values of resistors R2 and R3:

where R1 is the internal resistance of the signal source;

R4 - resistance matched load TEM strip line.

An example of the results of calculating the resistance values of the matching device R2, R3 depending on the characteristic line resistance (for the matched line is R4) for a TEM strip line with a width of upper and lower current conductors of 6 m for some suspension heights of the upper current lead with an output resistance of the signal source R1 = 50 Ohm is shown in table 1. In FIG. 6 shows the dependence of the resistances R2 (dashed line) and R3 (dash-dotted line) of the matching device on the height of the suspension of the upper current lead from 0 to 6 m.

The principle of configuration and operation of the device is as follows (Fig. 1): the flexible conductors of the lower current lead 1 are laid on the underlying surface and connected on the one hand to the clamps for fixing 5 on the transition section 3, and on the other hand, to the clamps for fixing 6 on the load 4 .

Flexible conductors of the upper current lead 2 are suspended from the dielectric trusses 9, they rise to a predetermined height. After that, the flexible conductors of the upper current lead 2 on the one hand are connected to the clamps 7 for fixing on the transition section 3, and on the other hand, to the clamps 8 for fixing on the load 4.

At the same time, the length of the conductors, their number and the distance between them are selected in such a way that the width and length of the working volume of the TEM strip line should be no less than 30% greater than the transverse dimensions of the test object, and the working volume should be at least 2 times larger the height of the test object.

The wave (characteristic) resistance of the strip line Z _in , the matched load R4, and the resistances of the adjustable matching device in the form of a L-shaped resistive four-terminal R2, R3 are calculated. The sets of resistors of the matching device and the matched load are switched under the calculated parameters of the wave (characteristic) resistance of the TEM strip line by connecting the corresponding jumpers between the resistive elements of the sets of resistors 19 and 23 of the matching device of the transition section 3 and the resistive elements of the set of resistors 31 of the adjustable matched load 4.

The correctness of the adjustment of the matching device is checked by connecting to the coaxial connector 16 the transition section of the device for measuring the standing wave voltage coefficient (VSWR). An example of measuring the frequency dependence of the standing wave coefficient by the voltage of the TEM strip line when using a matched load and matching device, and without them is shown in FIG. 7.

A source of a powerful signal 32 is connected to the coaxial connector 16 of the transition section 3 - when it is turned on, a TEM wave propagates inside the strip line, which is absorbed in a matched load.

Claims (6)

A two-electrode TEM strip line with variable dimensions, tunable load and a matching device, containing a transition section in series with a connector for connecting a signal source, a matching device in the form of a L-shaped resistive four-terminal device, a field-forming system and a load, characterized in that the field-forming system is made with a variable geometry and consists of an upper and lower wire conductors and a lifting mechanism with dielectric trusses, the length and width of the plane-parallel part of the upper and lower conductors are made not less than 30 percent more than the length and width of the test object, the distance between the plane-parallel part of the upper and lower current conductors is made not less than than 2 times the height of the test object, the resistive elements R2 and R3 of the matching device are made in the form of a set of switched resistors and their values are determined by the expressions

where R1 is the resistance of the signal source connected to the two-electrode TEM strip line, R4 is the resistance of the matched load, the matched load is made as a set of switched resistors, and its resistance is chosen equal to the wave (characteristic) resistance of the two-electrode TEM strip line for the selected test object Z _in (R4 = Z _in ), which is calculated by the formula

where I is the total current in the conductors of the upper or lower current lead, U is the potential difference between the conductors.

Images