EP0983520A1

EP0983520A1 - Method and device for generating and receiving electromagnetic fields for test and measurement purposes

Info

Publication number: EP0983520A1
Application number: EP98928241A
Authority: EP
Inventors: Jörg FUNCK; Diethard Hansen; Detlef Ristau; Stefan MÖBLER
Original assignee: Euro EMC Service Dr Hansen GmbH
Current assignee: Euro EMC Service Dr Hansen GmbH
Priority date: 1997-05-21
Filing date: 1998-05-11
Publication date: 2000-03-08
Also published as: WO1998053333A1

Abstract

The invention relates to a measurement and test method and two testing device for EMV measurements, particularly for electromagnetic field radiation and irradiation with electronic and electrical apparatus and systems. In addition to permitting EMV measurements and tests which can be correlated with other standardized measurement procedures, said method and device also make it possible to carry out highly precise field calibrations. Said method is characterized in that an electromagnetic field is guided between the inner conductors at maximum energy concentrations, and that the flow of electricity from the inner conductors across the screen is largely suppressed and the polarisation of the TEM waveguide can be adjusted. The first device is configured in such a way that at least two inner conductors (6) situated opposite each other and having a flared shape are symmetrically fed at their tip (6a) via a balun (7) and that the inner conductors (6) are connected in an electrically conductive manner via resistors (1) to a first rear wall (3a) and/or a second rear wall (3b). The second device provided for by the invention has at least four inner conductors having a flared shape which are arranged in such a way that symmetrical, pair-by-pair feeding to the tips of the inner conductors forms pairs which, at their ends, are individually sealed against an absorber-covered, conductive rear wall so as to have the correct impedance.

Description

Methods and devices for generating and receiving electromagnetic fields for testing and

Measuring purposes

description

The invention relates to a method and devices for generating and receiving electromagnetic fields and is used in particular for electromagnetic field radiation and radiation in electronic and electrical devices and systems, for example for EMC measurements.

In addition to EMC measurements and tests, which can be correlated with other standardized measuring methods, high-precision field calibrations and further applications based on the method according to the invention and the devices can also be carried out. This affects both sinusoidal and pulsed fields. Another application is for backscatter measurements on material samples. It is also possible to determine the radiation patterns of certain antennas and to irradiate objects.

A first device according to the invention is designed as a funnel-shaped, electrically symmetrical strip conductor, in which TEM cells are generated, and which is either permanently integrated in its own screen or can be built into existing absorber chambers. A second device according to the invention has at least four widened inner conductors, which are arranged in such a way that pairs are formed by symmetrical feeding at the tips of the inner conductors, which at their end are individually terminated correctly at an absorber-covered conductive rear wall.

The geometrical shape of the outer screen is not of decisive importance for both devices, since it should not be integrated into the current return line. The screen can e.g. have a special pyramidal shape or also be cuboid.

Various apparatuses are already known which are used as waveguides for the generation of TEM waves. The prior art is described in DE 195 49 246. There, a pyramid-shaped arrangement is disclosed which can be rotated about the longitudinal axis during the measurement and which represents a symmetrical TEM cell with wire-shaped inner conductors. The TEM cell is lined with electromagnetic absorbing material on the two side walls and the rear wall, and the inner conductors are terminated at the end with resistors directly to the screen. The shield directly above or below the inner conductor is included in the current return line. The rear wall is curved and the terminating resistors are arranged in a circular arc in front of it.

A disadvantage of this arrangement is that most of the energy is concentrated in the space of only 2.5 cm between the shield and the inner conductors, and the field in the test volume is therefore relatively compared to the input power and parasitic effects is weak. This affects precision, especially at high frequencies.

Another disadvantage is the costly serrated plate on the feed, which is associated with a considerable adjustment effort.

In the device according to DE 295 21 476, too, the major part of the energy is not transported between the two inner conductors composed of individual wires, but between the inner conductors and the shield walls directly above or below. In this regard, the conditions are similar to those in the previously described arrangement according to DE 195 49 246. Only the rear wall, possibly the front wall and the side walls, should be clad with absorbers, while the screen walls lying directly above and below the wires together with the Wires form the asymmetrical line systems described there.

Inadequacies in the field quality also arise at kinks in the TEM waveguides, e.g. with classic TEM cells of the Crawford type or in DE 44 31 480 during the transition from the expanding part to the parallel part. At these discontinuities, secondary waves are excited which overlap the generated TEM wave.

The implementation of inner conductors through narrow slots in the absorber walls, but especially if, as in DE 195 01 329, ferrite absorbers are involved, results in reflections from the line wave, which ultimately also reduce the field quality. Due to the high permeability of the ferrite absorbers, the current flow becomes in some frequency ranges Resistances largely obstructed due to the inductance acting at this point.

With electrically asymmetrical TEM waveguides such as DE 44 31 480 or DE 195 01 329 will only spread a maximum of 50% of the energy fed into the test room. E.g. If the space under the inner conductor is used for the test object, the other part of the energy in the space above the inner conductor will remain unused. Although significantly more energy is carried in the test room than in the previously described arrangements according to DE 195 49 246 and DE 295 21 476, at the same time the unused part of the room (above the inner conductor) also accounts for a significant part of the total volume, so that Given the test specimen volume, the electrically asymmetrical arrangement compared to the electrically symmetrical arrangements as a whole is significantly increased in terms of the volume converted.

The invention is therefore based on the object when using the volume advantages of the electrically symmetrical waveguide to provide a method and devices for generating and receiving electromagnetic fields, in particular for testing and measuring purposes, the method providing highly effective, low-loss operation at a high energy concentration in the Test volume enables and the devices can be inexpensive, manufactured and adjusted with little effort.

This object is achieved according to the invention by the features in the characterizing part of claims 1, 11 and 17. Useful embodiments of the invention are contained in the subclaims. A particular advantage of the invention is the effective generation of a high energy concentration in the test volume, that is to say inside the cell between the pyramid-shaped inner conductors, by largely preventing the return of current via the screen and thereby transporting the main energy between the inner conductors through the test volume.

In the first implementation variant of the invention, the construction is fed symmetrically via a balun at the top of the two, for example triangular, inner conductors designed as metallic plates. In order to prevent the current return via the pyramid-shaped screen, all four side walls and the rear wall of the screen can be covered with absorbent material e.g. Ferrite tiles are clad. The rear wall can be constructed both straight and curved. There are various options for terminating the resistance, with the current shortly closing on the inside of the rear wall.

A particular advantage of the second implementation variant of the invention is the electrical switchability or pivotability of the polarization of the TEM waveguide, which is achieved in that at least four widened inner conductors are arranged in such a way that symmetrical feed to the Pointed pairs are formed, which are terminated individually at the end on an absorber-covered conductive rear wall with correct impedance.

The invention will be explained below with reference to exemplary embodiments which are at least partially shown in the figures. Show it: Fig. 1 TEM waveguide with two inner conductors and with a rear wall according to a first device

Fig. 2 TEM waveguide with two inner conductors and with its own second rear wall isolated from the screen according to the first device

3 shows an implementation variant of a second device with four inner conductors

3A shows an enlarged illustration of the balun area according to FIG. 3

Fig. 4 cross-sectional view of the TEM waveguide of Fig. 3 with shield

Fig. 5 feed into the TEM waveguide of FIG. 3 switchable for vertical and horizontal polarization

Fig. 6 feeding into a TEM waveguide with 8 inner conductors as a further implementation variant

Fig. 7 design of the current paths and arrangement of the terminating resistors at a. TEM waveguide with eight inner conductors corresponding to FIG. 6

As shown in FIG. 1, the simplest form of implementation with respect to the first device is to conductively attach the resistors 1 arranged on the inside of the screen 4 to the rear wall 3. When using ferrite absorbers, make sure that Current paths 2 are kept clear to ensure the flow of electricity. This can be implemented in such a way that the area around the resistors 1 and the path to the respectively opposite resistor 1 is not covered with absorbers, or a corresponding earth strap is applied to the absorbers at these points. The reason is the high dielectric constant of the ferrite absorbers, which changes the characteristic impedance by increasing the capacitance. Another reason is the high permittivity number, which makes the current path too high-resistance due to an increase in inductance. Contrary to the designs known from the prior art, no current flow is to be expected in the case of narrow cutouts for carrying out the resistance terminations or the waveguide. When using pyramid absorbers, the back wall can be completely covered, since dielectric and permeability are low. Only too close proximity of the absorbers to the septa can be avoided by introducing corresponding cutouts in the absorbers due to the impending increase in capacity.

A second possibility, as shown in FIG. 2, is to use two rear walls 3a, 3b lying one behind the other, so that the current can additionally flow unhindered on the rear side of the first rear wall 3a which is not lined with absorbent material. The second rear wall 3b closes the screen 4 and, like this, can additionally be coated on the inside with absorbent material. In addition, the first rear wall 3a can additionally be arranged in an electrically completely insulated manner from the second rear wall 3b. The only conductive connection of the shield to the internals is then through the socket 8 inserted into the shield. This leaves the possibility of mechanical rotation of the septa within the fixed housing. The screen 4 does not necessarily have to be pyramid-shaped, as shown in FIG. 2, but can in principle have any shape, since the surface currents on the inside of the metallic screen are strongly damped by the complete ferrite absorber lining and thus the Shield is not involved in the return of current. So the screen could, for. B. can also be designed cuboid.

As a third possibility, based on the first possibility, instead of a separate shield 4 lined with absorbent material, the TEM waveguide can be installed cost-effectively in already existing full absorber chambers and in this case the absorber chamber can be used as a shield. In the case of ferrite absorber chambers, the installation can be carried out in such a way that earth strips for the creation of the required current paths 2 are first glued to the wall to which the resistors 1 are to be attached. The resistors 1 are then conductively connected to these ground straps.

In all three cases, the cost-saving is compared to the prior art by dispensing with the costly serrated plate at the feed, which is associated with a considerable adjustment effort. In addition, due to the distance, the stripline must be constructed with a significantly higher impedance, for example with a 200 ohm characteristic impedance. The balun 7 arranged at the tip 6a of the inner conductor can also be used for resistance adjustment (for example 1: 4 balun) in addition to symmetrization. With the same input power at the 50 ohm socket 8, a higher electrical field strength can be achieved in the test volume in the case of field radiation. In addition, there is a significant simplification of production, because a stripline with a few hundred ohm wave impedance (large distance between the two inner conductors 6 as a forward and return conductor) can be constructed with significantly greater distance tolerances than a 25 ohm waveguide (small distance between the inner conductor and the screen as a forward and return conductor). As a spacer between the inner conductor 6 and screen 4 or between the first and second rear walls 3a, 3b, for example, rigid foam blocks or rigid foam plates can be used. The door can be arranged both in the side walls 5 and in the rear wall 3a, 3b.

FIG. 3 shows an embodiment of the second device with four inner conductors. In this case too, the waveguide is later installed in a screen 15 completely lined with ferrite absorbers 14a, as the cross-sectional illustration in FIG. 4 shows. The geometrical shape of the outer screen 15 is not of crucial importance, since it should not be integrated into the current return line due to the covering with ferrite absorbers 14a. The screen 15 can, for example, have a pyramid-like shape or also be cuboid in order to achieve a cross section corresponding to FIG. 4. In the rear wall 14 of this screen 15 there are current paths 12 not covered by absorbers 14a. The implementation of corresponding current paths can also be achieved by applying corresponding metallic ground straps to the ferrite absorbers 14a. Each inner conductor 11 is terminated with resistors 13 individually on these current paths 12 with correct impedance. If possible, the current paths 12 are arranged in the edge region of the TEM conductor cross section in order to minimize field reflections in the test volume. As in the example shown, the inner conductors 11 can be implemented most simply by triangular metal strips. In principle, however, it is also possible to use other inner conductor cross sections, however, in order to achieve a wave resistance that is constant over the length, their cross section must widen continuously to the same extent as the overall structure. In the case of round cross sections, this leads, for example, to conically widening conical inner conductors 11. By inserting a switching device 19, which is not explicitly shown in the figures, between the tips 11a of the inner conductors 11 and the balun 17, it is possible to determine the polarization of the TEM wave in cross section from to switch vertical E-field polarization to horizontal E-field polarization. In the first case, the horizontal and in the second case the vertically adjacent inner conductors 11 are connected in pairs at the tip (FIG. 5). Implementation possibilities for the switchover device 19 are, for example, a plug-in connection which allows the balun 17 to be plugged onto the four inner conductors 11, also rotated 90 °, or a correspondingly constructed rotary switch.

If the arrangement is expanded to include further pairs of inner conductors, further polarization angles can be set if the arrangement is appropriate. With a total of six inner conductors 11, the polarization can be set in 60 ° steps, with eight inner conductors 11 in 45 ° steps and with another even number of inner conductors n in 360 ° / n steps.

6 shows a possible implementation for the configuration of the feed and FIG. 7 for the termination of a TEM waveguide with eight inner conductors 11, the inner conductors 11 being arranged in an octagon. With this arrangement, the polarization of the TEM Shaft can be set in 45 ° steps. When feeding in, attenuators 16 can be used to ensure that adjacent inner conductor pairs are subjected to a correspondingly lower RF voltage than the middle pairs. The voltage to be set must be inversely proportional to the average inner conductor spacing in order to obtain a field distribution between the inner conductors 11 that is as uniform as possible in the entire interior.

If each individual inner conductor 11 is terminated individually with an "active balun", the direction of polarization can also be set fully electronically. In the case of transmission, such an "active balun" consists of power RF transistors which are driven by a power splitter with the correct amplitude and with a switchable phase position. In the case of reception, an amplifier made of RF transistors is controlled via an adaptation network, the amplification of which can be set, the phase position of which can be switched and the outputs of which are interconnected via a power combiner.

It is not only possible to operate the waveguide with an adjustable constant polarization. A phase-shifted feed can also generate a rotating polarization (circularly polarized wave). In the case of the implementation example with four inner conductors 11, for example two voltages offset by the phase angle 90 ° can be connected simultaneously, each of these voltages being fed between two diagonally opposed inner conductors 11. Another possible variation is to replace the terminating resistors 13 with open circuit or short circuit. In the low frequency range, low-frequency electrical or low-frequency magnetic fields can be generated, for example for certain 50 or 60 Hz mains frequency tests, so that no extra devices such as special magnetic frames etc. are required for these simple tests either.

The invention is not restricted to the exemplary embodiments described here. Rather, it is possible to implement further design variants by varying the means and features without leaving the scope of the invention.

Reference list

1 resistors

2 current paths 3 rear wall

3a first rear wall

3b second rear wall

4 umbrella

5 side walls of the screen 6 inner conductors

6a tip

7 balun

8 socket

11 inner conductor Ha tip

12 current paths

13 terminating resistor

14 rear wall 14a absorber 14b central region of the rear wall

14c edge area of the rear wall

15 umbrella

16 attenuator

17 balun 17a balun and switching device

18 socket

19 switching device

Claims

claims

1. A method for generating and receiving electromagnetic fields with an object located within a TEM waveguide, wherein either the object is subjected to defined parameters or the electromagnetic radiation emitted by the object is measured, characterized in that an electromagnetic field with maximum energy - Concentration between the inner conductors and a current flow from the inner conductors via the screen is largely suppressed and the polarization of the TEM waveguide is adjustable.

2. The method according to claim 1, characterized in that the prevention of the current flow is carried out by targeted specification of current paths with suitable impedances.

3. The method according to claim 2, characterized in that the current paths including the ground paths act on the rear wall with low resistance.

4. The method according to claim 1, characterized in that the electromagnetic field is continuous or pulse-shaped.

5. The method according to claim 1, characterized in that the polarization is mechanically adjustable by rotating the TEM waveguide about its longitudinal axis.

6. The method according to claim 1, characterized in that the polarization is adjustable by electrical or electronic switching processes with a fixed TEM waveguide.

7. The method according to claim 1, characterized in that the inner conductors are fed in such a way that a constant or rotating polarization is realized in the generation and feed-in of the electromagnetic fields.

8. The method according to claim 1, characterized in that at the external resistance, the resistance value idle for generating electrical fields or Short circuit for generating magnetic fields is set.

9. The method according to claim 1, characterized in that the generation of electromagnetic fields takes place via an "active balun", which consists of power RF transistors that are driven with a correct amplitude and switchable phase from a power splitter.

10. The method according to claim 1, characterized in that the reception of electromagnetic fields via an "active balun", which consists of RF transistors, the amplification is adjustable, the phase position is switchable and the outputs are interconnected via a power combiner.

11. Device for generating and receiving electromagnetic fields with an approximately pyramid-shaped TEM waveguide made of septa inside a cell forming a screen with absorbing walls, characterized in that at least two opposite, expanding inner conductors (6) at their tips (6a ) are fed symmetrically via a balun (7) and the inner conductor (6) via resistors (1) a first rear wall (3a) and / or a second rear wall (3b) are electrically conductively connected.

12. The apparatus according to claim 11, characterized in that the inner conductor (6) are triangular.

13. The apparatus according to claim 11 or 12, characterized in that the inner conductor (6) are metallic plates.

14. The apparatus according to claim 11, characterized in that the inner conductor (6) consist of wires.

15. The apparatus according to claim 14, characterized in that the wires are arranged in a grid or form stitches.

16. The apparatus according to claim 11, characterized in that between the inner conductors (6) and / or the screen (4) and / or between the first rear wall (3a) and the second rear wall (3b) hard foam blocks and / or hard foam plates are arranged.

17. Device for generating and receiving electromagnetic fields with an approximately pyramidal or conical TEM waveguide made of septa inside a cell forming a screen with absorbing walls, characterized in that at least four expanding inner conductors (11) are arranged such that pairs are formed symmetrically in pairs at the tips (11a) of the inner conductors (11), which are terminated individually at the end on a conductive rear wall (14a) covered with absorbers (14a) via resistors (13) with correct impedance.

18. The apparatus according to claim 17, characterized in that the central region (14b) of the rear wall (14) is completely covered with absorbers (14a) and the resistors (13) in the edge region (14c) of the rear wall (14) via ferrite-free current paths (12th ) are connected.

19. The apparatus according to claim 17, characterized in that the inner conductor (11) are metallic plates which are approximately triangular.

20. The apparatus according to claim 17, characterized in that the inner conductors (11) have a round or oval or trapezoidal cross section, which widens in a conical shape.

21. The apparatus according to claim 17, 19 or 20, characterized in that each inner conductor (11) has a constant wave resistance over its length.

22. The apparatus according to claim 17, characterized in that either four inner conductors (11) on a square cross-section, switchable for 90 ° rotation or two times four inner conductors (11) nested into an octagon, switchable for 45 ° rotation or eight inner conductors (11) on a square cross-section, switchable for 90 ° rotation or any even number of inner conductors (11), which are arranged two-axis symmetrically on any cross-section.

23. The device according to claim 17, characterized in that with more than four inner conductors (11) for attenuation correct amplitude additional attenuators are arranged on the individual inner conductors (11).