Tunable matching network

Details Tunable matching network Tunable matching network

1994-01-04

1995-07-04

Gensler, Paul

Wave transmission lines and networks

Coupling networks

With impedance matching

333 241, 333263, H01P 504

Patent

active

054304172

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a tunable matching network which may be coupled to a microwave transmission line.
2. Brief Description of the Related Art
As indicated in a presentation by F. Durodie on New Antenna Impedance Evaluation and Matching Tools for TEXTORS's ICRH System, at the 16th Symposium on Fusion Technology (SOFT), London, Sep. 3-7, 1990, a tunable matching network, is required, for example, for a microwave transmission line which couples high power microwave energy into the plasma combustion chamber of a fusion reactor. Since the plasma combustion chamber represents a constantly changing load resistance to the microwave transmission line and in order for the generator generating the microwave energy not to be damaged by reflections which are the result of a mismatch, each occurring load resistance must be transformed to the characteristic impedance of the line. According to the mentioned publication, two tunable capacitors which are separated from one another by the length of a transformation line, which must be measured precisely, are coupled to the microwave transmission line for this purpose. Tuning of the capacitors is the result of a mechanically elaborate pneumatic device. However, since the load resistance may change very rapidly, this arrangement would be too slow to bring about matching that is as free of delay as possible.
A tunable matching network may not only be used in the case described, but at any time a changing resistance impedance is switched on to a microwave transmission line.


SUMMARY OF THE INVENTION

It is the object of the invention to provide a matching network which may be rapidly tuned to a desired impedance at low expense.
According to the invention, this object is attained by a tunable matching network having first and second lines each having a first and a second end, the first ends of the first and second lines being connected together and the second ends of the first and second lines each being adapted for coupling to a microwave transmission line, and at least one of the first and second lines being loaded with ferrite material, a third line having one end coupled to and branching off from the first ends of the first and second lines and being loaded with the ferrite material, and means for generating and exposing the ferrite material of the first and second lines and the ferrite material of the third line to separate magnetic fields which are independently chargeable for turning the matching network.
Due to the fact that the matching network may be tuned electrically without any mechanically movable parts, impedance matching that is free of delay is ensured when the load resistance of the microwave transmission line changes rapidly.
A further advantage of the arrangement is that no transformation line is required between the two variable reactances of the matching network mentioned above.


BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further elucidated by means of an embodiment shown in the drawing in which:
FIG. 1 is a longitudinal view of a matching network and
FIG. 2 is a perspective illustration of the same,
FIG. 3 is an equivalent circuit diagram of this matching network.


DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a longitudinal section and FIG. 2 is a perspective illustration of a tunable matching network, which is coupled to a microwave transmission line L. In the illustrated embodiment, the microwave transmission line L is a coaxial line having an inner conductor LI. As already mentioned in the introduction, and as illustrated by the equivalent circuit diagram in FIG. 3, the microwave transmission line L is fed at its input by a generator G and is terminated at its opposite output by means of a changing load resistance ZL. The T-equivalent circuit diagram which includes impedances Z1 and Z2, and which is inserted into the microwave transmission line L, represents the matching network, which serves to transform the respective load resistance ZL to the characteristic

REFERENCES:
patent: 2403252 (1946-07-01), Wheeler
patent: 3384841 (1968-05-01), Di Piazza
patent: 3681716 (1972-08-01), Chiron et al.
patent: 3745488 (1973-07-01), Rogers
patent: 3792385 (1974-02-01), Napoli et al.
patent: 4754229 (1988-06-01), Kawakami et al.
patent: 5065118 (1991-11-01), Collins et al.
IRE Transactions on Microwave Theory and Techniques. vol. 7, No. 2, Apr. 1959, New York US, pp. 296-297. C. E. Muehe: "Quarter-wave compensation of resonant discontinuities".
F. Durodie: New Antenna Impedance Evaluation and Matching Tools for Textor's ICRH System, at the 16th Symposiom on Fusion Technology (SOFT), London, Sep. 3-7, 1990.

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