Wave transmission lines and networks – Long line elements and components – Waveguide elements and components
Patent
1997-03-14
1998-09-22
Gensler, Paul
Wave transmission lines and networks
Long line elements and components
Waveguide elements and components
333 35, H01P 108
Patent
active
058120408
DESCRIPTION:
BRIEF SUMMARY
This application claims the benefit of U.S. Provisional application Ser. No. 60/001,208, filed Jul. 18, 1995.
BACKGROUND OF THE INVENTION
The present invention relates to large diameter microwave waveguides, and more particularly to a distributed window that may be used in such waveguides to couple high frequency, high power microwave radiation through a vacuum barrier within the waveguide without overheating, significant mode conversion, or reflection of incident power. Even more particularly, the invention relates to the use of an impedance transition built into the vanes of the vacuum barrier to increase the bandwidth of the window. Such impedance transition, which comprises one or more quarter wave matching sections in the individual vane structure, makes the dielectric material used as part of the vane structure non resonant. In turn, this non resonant condition reduces the power dissipated in the dielectric, and thereby increases the power handling ability of the window.
A waveguide window in a microwave power system permits power to be coupled from a first waveguide to a second waveguide, but presents a physical barrier between the two waveguides. The physical barrier allows the waveguides to contain different gases or to be at different pressures, and one or both waveguides may be evacuated. For example, in high power microwave vacuum devices, such as gyrotrons and the like, the output power must be coupled between an evacuated chamber or waveguide in the gyrotron device, through one or more waveguide windows, into a waveguide having a gaseous environment. The one or more waveguide windows thus provide a hermetic seal between the two media. Also, in fusion reactors where microwave power is added to a plasma, the physical barrier of a microwave window may be placed near the reactor to confine the constituents of the plasma.
One type of microwave window known in the art is a double-disk window. A double-disk window can be tuned over a limited frequency range to compensate for errors in window thickness or unit-to-unit variation in gyrotron output frequency.
Another type of microwave window known in the art is described in U.S. Pat. No. 5,061,912, incorporated herein by reference. The type of microwave window disclosed in the '912 patent is a distributed window that forms part of a phase velocity coupler. The type of coupling provided by the described window is between two identical corrugated rectangular waveguides, each of which is many (e.g., >15) free space wavelengths, .lambda..sub.0, wide in one transverse dimension but only 2 to 3 .lambda..sub.0 in the other dimension. A transition from circular corrugated waveguide many .lambda..sub.0 in diameter propagating the HE.sub.11 mode, which is a preferred method of low loss transmission for high power millimeter wavelength microwaves, to this rectangular corrugated waveguide, can always be made. However, if the circular waveguide is very large, e.g., 30.lambda..sub.0 in diameter, many modes which can propagate in the larger circular waveguide are cut off in the rectangular waveguide. Although ideally, only one mode is emitted from the source, typically a gyrotron, and propagated through the system, in reality there is often a few percent of other modes present, which might be reflected back to the source with deleterious effects by such a transition. Hence, there is a need in the art for a microwave window that can be used to directly and efficiently couple high frequency microwave power between two large diameter waveguides without the need for any transitions to other shapes and sizes.
Such needs are met, at least in part, by the large diameter distributed microwave windows disclosed in applicant's prior U.S. Pat. No. 5,313,179 and 5,400,004. Advantageously, such large diameter microwave windows are particularly well-suited for use with the new generation of gyrotrons, such as the Russian 500 kw, 110 and 140 GHz gyrotrons which have the HE.sub.11 output mode, which are most compatible with a large output diameter. Unfortunately, however, depe
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International Search Report dated Oct. 25, 1996 for International Application PCT/US96/11758.
1986 IEEE-MTT-S International Microwave Symposium--Digest, Jun. 2-4, 1986, Baltimore, USA, pp. 151-154, deRonde: "An octave-wide matched impedance step and--quarterwave transformer".
General Atomics
Gensler Paul
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