HU192481B - Coaxial impedance transformer - Google Patents

Abstract

Coaxial circuits with different wave impedance, systems with high accuracy adaptable coaxial impedance transformer can be changed wave impedance feeder lines and can be changed at the junction points of the sections capacities. Has a variable wave impedance Feed Line Lines Flat Lead metallic conductive sections above base plate (1) (2) make up. The leading sections (2) are metallic conductors islands (3) rely on them for example. soldering recorded. Can be changed to this metallic guide island (3) capacities are also connected or known RF trimmer design or carrier plate capacitive digital capacities from leading islands (3b). The flat leading base plate (1) and the enclosing metal housing (6) gives the grounded branch of the coaxial system while the conductor sections (2) with the supporting islands and their associated capacities form the coaxial system inner blood. (Figure 3)

Description

The present invention relates to a coaxial impedance transformer for adapting coaxial power line sections and circuits with different wave impedances.

Coaxial radio frequency circuits are used in different waveguide variants. However, there are cases where it becomes necessary to connect two systems with different wave impedances for common operation or measurement. Impedance transformers must be used to connect systems with different wave impedances. These transformers, subject to different ratios, meet strict fitting conditions.

The stringent requirements for impedance transformers are met by different designs in different frequency bands, with little or no compromise. The currently known and widespread coaxial impedance transformers consist of concentrated L-C elements in the lower frequency bands (below 100 MHz). Impedance transformers made of coaxial cables are also rarer, with less tight joints. For example, a 50 ohm and 75 ohm system can be interconnected by a quadrature 60 ohm power line section; 1: 1.3 with a standing wave ratio.

At higher frequencies (above 500 MHz), a λ / 4 impedance transformer consisting of rigid coaxial feeder lines is used in 1-2 or 3-phase designs. With high precision manufacturing, such transformers meet the most stringent requirements. They are characterized by their rugged design and relatively high weight, so they are only suitable for higher performance. They are spread in the upper half of the UHF band and in the microwave range, in the latter case with waveguide feed lines, where the length of the λ / 4 feed line sections gives acceptable dimensions.

However, there are only compromise solutions for the impedance transformers used in the 100 to 500 MHz band of the VHF band. Either they build a circuitry of concentrated elements whose characteristics are not exaggerated, or they use the powerline technology to solve the problem of fitting at large dimensions. A typical example of a 50/200 ohm asymmetric-to-symmetric transformer with a concentrated element is the Rohde-Schwarz BSI-type impedance transformer family, which provides precise impedance matching for measurement purposes with tunable inductors.

For the application of powerline technology, see IEEE-MTT Volume 19, pp. 415-416. The following pages show a typical application example of an impedance matching network implemented with a direct interface. Another application example belongs to the family of stripline circuits, which are described in detail in IEEE-MTT Volume 21, pages 69-75. This design assumes high precision film etching technology and does not achieve accurate reflection with low reflection even for measurement purposes.

To overcome these drawbacks, it is an object of the present invention to provide an impedance transformer capable of accommodating different coaxial impedances in frequency ranges above 100 MHz, and that the accuracy of the coupling not only meets the lighter requirements of operation, but also stricter requirements for measuring arrangements; in addition, considering the lower power operation and measurement, the design should be lightweight and optimally small in volume, as opposed to rigid power line segment designs.

The objects are achieved by providing inductances from conductive sections extending over a conductive base plate, preferably of silver plated copper wire, at both ends of which are supported by metallic islands formed on a conductive base plate with a solid metallic bond.

Variable concentrated capacities are connected between the leading base plate and the metallic islands. These variable capacities are either high frequency trimmer capacitors of known design or interdigital capacitance islands that can be formed by means of the stripline technique. These embodiments result in several embodiments of the invention.

It is an essential characteristic of each embodiment that the inductance of the power line sections and the associated tuning capacities can be varied individually. In this way, the power line sections implementing the impedance transformation can also be tuned to each other to the desired degree and very precisely matched.

Thus, the present invention utilizes variable-wave impedance power line sections interconnected in a circuit that accommodate different wave impedances between two adjacent connecting sections. Low-reflection precision matching between the input and output impedances and adjacent sections of the connecting power line is achieved by providing the ability to vary the inductive sections and the concentrated capacities of the present invention.

Variable inductances by supply line sections can be implemented as follows:

By known geometric transformation, the coaxial (con45 centric) arrangement can be flattened. After such a transformation, a shape is obtained in which a metallic conductor passes a certain distance above a flat conducting base plate. You can calculate the wave impedance of this arrangement using the following known formula:

2D

Z = 60 ln ~ o d, -g where the distance of the metallic conductor over the conductive base plate is D / 2 and the diameter of the metallic conductive segment is d.

It can be seen from the formula that changing the D / 2 distance gives the possibility to change the wave impedance Ζθ.

βθ It is also known in the literature that there is a relationship between inductance of supply lines and wave impedance:

-21 Γ

Formula Ε can also be considered as a measurement instruction. It is simply from this context that inductance:

L = Z C o can be tuned sensitively by changing the wave impedance due to the square relation. This fact is utilized by the present invention.

The use of variable wave impedance supply line sections does not occur with prior impedance transformer designs. The characteristics of the power line sections used in the stripline technique are determined by calculation and then produced by the technology of printed wiring. There is no way to fine tune it here, so adopt a more inaccurate but still fitting solution for operating conditions.

Better than this solution is the arrangement of using variable waveguide power line sections with fixed tuning capacities in accordance with the present invention. Variable-wave impedance, λ / 4 (or shorter) power line sections provide optimum adjustment of inductances and distributed capacities between switching elements scaled by known computational methods.

Another feature of the invention is an embodiment of tuning capacities. Capacity islands, which are related to the stripline technique, but which are used differently, are connected in the required amount to the connection points of the supply line sections. In this case, of course, a low-loss dielectric carrier layer, e.g. Teflon should be applied between the leading base plate in the layout and the capacity islands. Such carrier materials exist.

The conductive base board is preferably provided by copper foil on the double-sided (or single-sided) sheet of copper used in the printed circuit technology. The single-sided disc solution is cheaper but requires more volume due to the use of concentrated tuning capacities. In order to realize interdigital capacities, a double-sided foil plate is appropriate in this case. Then the metal interdigital capacitance islands on the mounting side give precisely calculated capacities to the other side (grounded) copper foil.

Detailed Description of the Invention

Fig. 1 shows a two-stage impedance transformer with concentrated trimmer capacities, Fig. 2 shows details of the connection of power line sections and interdigital capacitance islands, and

Figure 3 illustrates a flat, low-volume, two-stage impedance transformer using interdigital capacities.

In Figure 1, a guide section 2, preferably a silver-plated copper wire, is located above the guide base plate 1. This is a planar coaxial arrangement with a grounded portion of the conductive base plate 1. The conductive base plate 1 is provided with properly formed metallic conductive islands 3 which are not in metallic contact with the conductive base plate 1. The 3 metallic conductive islands are matched by the 2 conductive sections,

481 2 for 3 metallic conducting islands with a solid metallic bond, e.g. fixed by soldering.

The metallic conductive islands are configured so that they can also be connected to concentrated capacitive elements 4 (trim5 ders). The assembly is housed in a metal housing 6 with suitable coaxial connectors 5 on its sides.

In the case where the concentrated capacitive elements 4 are not implemented with many of the known trimmer capacitor types 10 but in an interdigital arrangement, the details are shown in Figure 2. One side of the double-sided Teflon sheet provides the guide base 1. In addition to the metallic islands 3a fixing the conductive sections 2, several interdigital capacity islands 3b are formed as shown in FIG. 2 using known etching technology. The size and number of interdigital capacity islands 3b are based on the characteristics of the foil plate used. The formed interdigital capacity islands 3b are connected to the centrally located metallic islands 3a by a metallic bond, preferably a tin-plated foil or copper wire. The number of islands required to be connected is determined by measurement and confirmed.

Another preferred embodiment of the present invention is illustrated in FIG. This arrangement is less voluminous than that shown in Figure 1, precisely because of the use of interdigital capacities. Here, the conductive base plate 1 is provided by the lower layer of the two side-lined Teflon substrates. By removing the excess areas of the top layer by etching, metallic conductive islands 3a and interdigital capacity islands 3b are formed. The conductive sections 2 are soldered to the metallic islands 3a, while the tuning capacity formed by the interdigital islands 3b together is connected.

In both embodiments of the impedance transformer of the present invention, two different coaxial systems interconnected by the impedance transformer are connected to the inputs and outputs of the impedance transformer via coaxial connectors 5. Any standard connector can be used here.

In any preferred arrangement according to the invention, the spacing between the metallic islands 3 determines the length of the feed line segment carrying the inductance, and thus the nominal value of the inductance. The purposeful folding of the power line segment does not alter the essence of the invention that variable power impedance power line sections are used. The inductances of the power line sections are set to a final value when the arrangement according to the invention is measured, with a slight deformation of the conductor blades 2.

The guide sections 2, preferably e.g. φ 1.5 ... 2, C mm silver plated copper wire shape, center line direction can be varied within certain limits as necessary. At the same time, the mechanical strength of the conductive sections 2 is sufficient to permanently maintain the controlled optimum position controlled by the measurement, with sufficiently low reflection of the impedance transformer.

The characteristics of the required number of power line sections for a given matching task in the VHF and UHF bands are known in the art, e.g. computer

192,481 are determined. With the data obtained, the arrangement according to the invention is prepared as a nominal value. The final values of the impedance transformer switching elements are set by measurement to the final magnitude, with minimal reflection and simultaneous recording of the required bandwidth.

The tuning and setup procedure is known and is not detailed. In the construction of the present invention, the final adjustments must be made after the metal housing 6 has been mounted, through the adjustment holes 7 provided for this purpose, with an insulating tuning rod.

Claims (5)

Coaxial impedance transformer for joining coaxial supply line sections of different wave resistances having inductive and related capacitive elements, characterized in that they are made of conductive sections (2) extending over a conductive section (2) extending over a conductive base plate (1) and the ends of these conductive sections (2) are supported by metallic conductive islands (3) formed on the conductive base plate (1) and are secured by a solid bond, preferably by soft soldering. A coaxial impedance transformer according to claim 1, characterized in that the metallic conducting islands (3) formed on the conductive base plate (1) are connected by capacitive elements (4) with one terminal and the other terminal with the conductive base plate (1). A coaxial impedance transformer according to claim 1, characterized in that the concentrated capacitive elements (4) consist of groups of interdigital capacitance islands (3b) and these interdigital capacitance islands (3b) are electrically bonded in the necessary amount to their respective (central) connected to metallic islands (3a). A coaxial impedance transformer according to claim 1 or 2, characterized in that the conductive base plate (1) and the metallic conductive (3) islands are formed on one side of a fiberglass epoxy carrier plate and the conductive sections (2) on the uncoated side of the carrier plate. Coaxial impedance transformer according to claim 1 or 3, characterized in that the metallic islands (3a) and the interdigital capacitance islands (3b) on one side of the conductive base plate (1) are copper foil on one side and the foil plate is on the other side. they are formed on the other side.