The invention will now be explained and described in greater detail on the basis of examples of embodiments, wherein reference is made to the appended drawing, the figures of which show as follows:
FIG. 1 a schematic drawing of a coupling of a coaxial cable into a hollow conductor;
FIG. 2 in section, an example of an embodiment of an arrangement for coupling according to the invention;
FIG. 3 the arrangement of FIG. 2 in a perspective drawing of a sectioned hollow conductor at a scale reduced compared to FIG. 2; and
FIG. 4 the arrangement of FIG. 3 in perspective, in the form of a view from in front, into the hollow conductor.
For simplification, equal components, modules and devices are given equal reference characters in the drawing.
The schematic drawing of FIG. 1 serves for general explanation of the arrangement 10 of the processes in the case of a coupling of high frequency, electromagnetic signals from a coaxial cable 12 into a hollow conductor 14, for example a round, hollow conductor. An inner conductor 16 of the coaxial cable 12 enters a rear wall 18 of the hollow conductor 14. The inner conductor 16 is continued in the hollow conductor 14 as an exciter pin 20, and an exciter pin tip 22 away from the rear wall 18 of the hollow conductor is connected electrically conductively with a sidewall 24 of the hollow conductor 14. As is known, of concern here is the converting of the TEM-wave in the coaxial cable 12 into a TE11 wave. To this end, the hollow conductor 14 is to be dimensioned such that no higher modes can be propagated except TEM and TE11, since they represent the lowest existing solutions of the Maxwell-equation. The disturbed rotational symmetry of the field distribution of the TEM-waves leads to an asymmetric field distribution of TE11-waves. Reflections at disturbances must be destructively interfered. These processes are illustrated by the flow diagram in the upper part of FIG. 1. The arrangement 10 has, for purposes of discussion, been divided into three sections A, B, C, with section A representing a region where the TEM-waves can propagate, section B a region where both TEM and TE11 waves can propagate, and section C a region where TE11-waves can propagate.
In order to achieve good coupling properties, the geometry of the arrangement 10 must be so optimized that the two reflected TEM-waves (see the diagram in the upper part of FIG. 1) destructively interfere, thus the case of a phase shift of, and the transmitted TE11-waves constructively interfere, thus the case of a phase shift of 2. With an abrupt transition of the exciter pin 20 at the sidewall 24 of the hollow conductor 14, however, as in the case of the example illustrated in FIG. 1, only a relative small bandwidth can be achieved. The invention solves this problem by making the transition of the exciter pin 20 onto the sidewall 24 softer than displayed in FIG. 1.
FIG. 2 shows an arrangement 10 of the invention made in this way, wherein the drawing of the coaxial cable (see FIG. 1) has been omitted. The inner conductor 16 of the coaxial cable is expediently situated in a glass feedthrough 28 in the rear wall 18 of the hollow conductor. Hollow conductor 14, for example a round, hollow conductor, is preferably filled with a dielectric material, preferably with a material formed of perfluoro-plastic, for example a polytetrafluoroethylene or perfluoroalkoxy-copolymer. The exciter pin 20 is embodied as a straight pin and extends in the hollow conductor at an angle inclined with respect to the sidewall 24. In the region, where the exciter pin electrically contacts the sidewall 24 of the hollow conductor 14, an appropriate groove is milled into the cylinder 26 of dielectric material filling the hollow conductor 14, so that, in the case of an already emplaced exciter pin 20, the cylinder 26 can be pushed into the hollow conductor 14. Expediently, the contacting of the exciter pin 20 is given extra attention, since it must be executed very carefully. Both at the contact of the exciter pin 20 with the conductor 16 of the glass feedthrough 28 and at the contact of the exciter pin 20 with the sidewall 24 of the hollow conductor 14, a high electrical current flows on the surface.
FIGS. 3 and 4 show the arrangement 10 of the invention of FIG. 2 in perspective representations. Visible are the hollow conductor 14, its rear wall 18, the exciter pin 20 and the glass feedthrough 28. For FIG. 3, a sectional drawing was selected, wherein the cylinder 26 (see FIG. 2) of dielectric material is not shown in this instance. FIG. 4 shows the arrangement 10 in a view from the front, thus into the interior of the hollow conductor 14.
All three FIGS. 2, 3 and 4 show clearly that the glass feedthrough 28 for the inner conductor 16 of the coaxial cable is arranged eccentrically in the rear wall 18 of the hollow conductor 14. Accordingly, the exciter pin 20 also sits eccentrically on the rear wall 18 in the interior of the hollow conductor 14.
Instead of the round, hollow conductor of cylindrical bore shown here, by way of example, for a special form of embodiment of the invention, also hollow conductors of conical bore can be used.
Tests have shown, that the arrangement of the invention for coupling is very well suited for use with fill level measuring devices of industrial measurements technology for determining fill level of a medium in a container or tank by means of high frequency, electromagnetic, measurement signals, which are transmitted to the medium and reflected on such, and then evaluated according to the travel-time principle.
LIST OF REFERENCE CHARACTERS
10 arrangement for coupling
12 coaxial cable
14 hollow conductor
16 inner conductor
18 rear wall
20 exciter pin
22 tip of the exciter pin
24 sidewall of hollow conductor
- A,B,C sections
Patent Application
20080003872
