US3213394A

US3213394A - Coupling between waveguides using arcuate slots with vacuum-tight dielectric window in region of low electric field

Info

Publication number: US3213394A
Application number: US337806A
Authority: US
Inventors: Liebscher Roland; Mayerhofer Erich; Veith Werner
Original assignee: Siemens AG
Current assignee: Siemens and Halske AG; Siemens AG
Priority date: 1963-01-18
Filing date: 1964-01-15
Publication date: 1965-10-19
Anticipated expiration: 1982-10-19
Also published as: DE1191875B; SE329420B; NL302812A; GB1018887A

Description

Oct. 19, 1965 R. LIEBSCHER ETAL 3,213,394

COUPLING BETWEEN WAVEGUIDES USING ARCUATE SLOTS WITH VACUUM-TIGHT DIELECTRIC WINDOW IN REGION OF LOW ELECTRIC FIELD 3 Sheets-Sheet 1 Filed Jan. 15, 1964 Fig.1

Oct. 19, 1965 R. LIEBSCHER ETAL 3,213,394

COUPLING BETWEEN WAVEGUIDES USING ARCUATE SLOTS WITH VACUUM-TIGHT DIELECTRIC WINDOW IN REGION OF LOW ELECTRIC FIELD Filed Jan. 15, 1964 5 Sheets-Sheet 2 Fig.5 2

O 1965 R. LIEBSCHER ETAL 3,213,394

COUPLING BETWEEN WAVEGUIDES USING ARCUATE SLOTS WITH VACUUM-TIGHT DIELECTRIC WINDOW IN REGION OF LOW ELECTRIC FIELD Filed Jan. 15, 1964 3 Sheets-Sheet 5 Patented 3,213,394 COUPLING BETWEEN WAVEGUIDES USING AR- CUATE SLOTS WITH VACUUM-TIGHT DIELEC- TRIC WINDOW IN REGION OF LOW ELECTRIC FIELD Roland Liebscher, Poing, near Munich, and Erich Mayerhofer and Werner Veith, Munich, Germany, assignors to Siemens & Halske Aktiengesellschaft, Berlin and Munich, Germany, a corporation of Germany Filed Jan. 15, 1964, Ser. No. 337,806 Claims priority, application Germany, Jan. 18, 1963, S 83,307 26 Claims. (Cl. 333-98) The invention disclosed herein is concerned with a transmission system for ultra high frequency electromagnetic waves, especially for use in connection with high capacity ultra high frequency tubes, comprising two wave guides which are mutually connected by way of at least one slot-shaped coupling opening which is' closed vacuum-tight by means of a dielectric window through which the electromagnetic wave energy passes from one wave guide to the other.

It is in connection with high capacity travelling Wave tubes customary to use for the coupling and decoupling of high frequency energy, :cross-sectionally preferably rectangular Wave guides. The wave guides are directly connected with the delay line in order to avoid contacting ditficulties. A part of the wave guides forms in this man ner, a part of the vacuum envelope of the tube and therefore must be closed vacuum-tight by means of windows made of dielectric material which windows are permeable by the high frequency waves. It is thereby important that the unavoidable losses occurring in the dielectric window remain small over as great a frequency range as possible. This may be achieved provided that no particular electric field increases appear at the window due to resonance elfects occurring at the desired transmission range.

In previously known transmission systems for electromagnetic ultra high frequency waves, comprising two Wave guides and a dielectric window for closing one wave guide with respect to the other, the dielectric window is always arranged so as to extend preponderantly in the range of strong electric fields of the ultra high frequency Waves which are to be transmitted. In the event that the operatively effective surface of the window extends parallel to the electric field vector, it is very difiicult to transmit high loads, owing to the great losses occurring in the window. Moreover, there is the danger of electrical breakdown along the surface of the window.

In order to prevent the danger of electrical breakdown in a dielectric vacuum-tight window which is arranged within a rectangular wave guide in a partition wall extending perpendicularly to the longitudinal axis of the wave guide, it is known to subdivide the window opening so as to form two slots between which extends a continuous metallic path along the region of the greatest electric field intensity of the TE -wave which is present in the wave guide. However, the losses in the window are not particularly reduced by this measure since the two slots lie as before preponderantly in the region of strong electric fields of the TE -wave. Moreover, this known arrangement represents a so-called resonance window the band width of which is known to be relatively narrow.

There is also known a transmission system for electromagnetic ultra high frequency waves, employing a dielectric window, such window being for the reducing of reflections arranged so that its operatively effective surface extends substantially perpendicularly to the direction of the electric field which preponderates on both sides in the transmission channels. An embodiment of this known transmission system comprises two cross-sectionally rectangular wave guide parts disposed in overlapping relation with the longitudinal axes extending in parallel, and having a dielectric window inserted at the juncture of the two wave guide parts. It was found that difficulties arise in connection with such an arrangement so far as the prevention of the triggering of undesired wave types (interference modes) is concerned. However, interference modes bring about considerable disturbance in the matching of the transmission channels to the window, causing in turn electrical field increases at the window and consequently an impermissible heating thereof.

In order to overcome the indicated difficulties, the invention proposes to provide in connection with an ultra high frequency system of the initially mentioned type, a coupling opening in the form of an arcuate slot which is arranged preponderantly outside a region of strong electric fields of the ultra high frequency waves which are present in the two wave guides, such slot partially embracing the respective region, and the total length of the slot of the coupling opening or openings exceeding half of the average operating wave length of the transmission system.

The magnetic field is as is known very strongly pronounced in a wave guide at the place of slight electric field intensity. In a transmission system according to the invention, there is therefore a strong magnetic coupling between the two wave guides which are arranged at the sides of the dielectric window. This magnetic coupling necessarily presupposes that the electric field vector is in the region of the coupling opening oriented parallel to the plane in which is disposed the coupling opening and therewith parallel to the surface of the dielectric window. The losses at the window are nevertheless extraordinarily slight since the electric field appearing in the slot is quite weak owing to the strong magnetic field. The coupling slot is advantageously of a configuration so that it extends approximately parallel to a magnetic field line which is present in the two wave guides at the place of great magnetic field intensity at average operating wave length.

The coupling slot of a transmission system according to the invention may be considered as a short-circuited Lecher line. Since an electromagnetic field is formed in a short-circuited line only in the vicinity of a resonance, the length of the slot is advantageously so dimensioned that the inherent resonance thereof lies approximately in the center of the desired transmission range of the system. The load coupled to the transmission system reduces the quality of the slot line very much so that the transmission range of the system becomes great. It has been found that a band width of one whole octave can be obtained with a transmission system according to the invention. Appropriate selection of the inherent resonance of the slot line makes it possible to provide for a condition in which all interference resonances of the slot line lie outside of the transmission range.

The various objects and features of the invention will appear from the appended claims and from the description of embodiments thereof which is rendered below with reference to the accompanying drawings.

FIGS. 1 and 2 indicate an embodiment of the invention as to the principles involved;

FIGS. 3 and 4 illustrate a structurally simple embodiment of the transmission system according to the invention; FIG. 4 representing a sectional view along the lines C-D in FIG. 3;

FIG. 5 shows in sectional view an embodiment in which the dielectric window is disposed between the overlapping wall parts of the two wave guides, a coupling slot being provided on each side of the window;

FIGS. 6 and 7 represent sectional views respectively along lines E-F and G-H of FIG.

FIG. 8 indicates an embodiment somewhat similar to the one shown in FIG. 5, but having a coupling slot only on one side of the window;

FIG. 9 shows an embodiment of the invention corresponding generally to the one represented in FIG. 8 but permitting a particularly simple assembly of parts; and

FIGS. 10 and 11 indicate in schematic manner an embodiment in which the two wave guides extend in perpendicularly crossing planes, FIG. 10 showing the arrangement from the top and FIG. 11 showing it from the side.

Referring now to FIGS. 1 and 2, the cross-sectionally rectangular wave guide 1 overlaps with its free end a further cross-sectionally rectangular wave guide 2 Which extends parallel to the longitudinal axis of the wave guide 1 and is staggered with respect thereto. An electromagnetic ultra high frequency wave is to be fed into the wave guide 1 in the direction of the arrow 3, such wave being propagated within the wave guide 1 in the form of an TE -wave. The ultra high frequency energy is from the wave guide 1 conducted into the wave guide 2 by way of coupling opening 4 which is arranged in the overlapping parts of the walls of the two wave guides and which is closed vacuum-tight by means of a dielectric material. As will be seen from FIG. 2, the coupling opening 4 is formed by an arcuate slot (coupling slot) which extends predominantly outside the range of strong electric fields of the TE -wave which spreads within the wave guide 1. The shape of the coupling slot is approximated to the shape of a magnetic field line H, shown in dash lines, at the place of great magnetic field intensity. It will also be seen that the length of the slot must be greater than would correspond to half the average operating wave length of the transmission system. (The limit wave length of the magnetic fundamental wave in the rectangular wave guide corresponds, as is known, to twice the width of the wave guide.) The coupling slot 4 is then operative as a short-circuited Lecher line. The electric field of the Lecher line is indicated by arrows E. The load flux from the wave guide 1 to the wave guide 2 results from the Poynting vector S. The losses in the dielectric which fills the coupling slot 4 are extraordinarily slight since the dielectric is loaded only by a slight electric field even in the presence of a high load fiux, owing to the strong magnetic coupling.

In the constructionally simple embodiment indicated in FIGS. 3 and 4, the rectangular wave guide 1 is soldered to the end of a delay line 5 of a travelling wave tube, the longitudinal axis of the wave guide extending perpendicular to the longitudinal axis of the delay line. The wave guide 1 overlaps, as in FIG. 1, a rectangular wave guide 2 which extends parallel to the longitudinal axis of the wave guide 1 and is staggered with respect thereto. The two wave guides 1 and 2 border directly on one another with their wide sides and therefore have in the region of the overlap a common wall.

This common wall has in the center thereof a circular breakthrough in which is inserted a ceramic disk 6. The ceramic disk 6 carries on each side thereof a circular metallizing 7. In this manner is formed an annular coupling slot 4 which is filled with dielectric material, such slot embracing a region of strong electric fields of the TE -wave which is propagated in the two wave guides. The ceramic disk 6 with the metallizing 7 is so dimensioned that the average circumference of the coupling slot 4 coincides in approximation with the circumference of a magnetic field line which forms at average operating wave length in the

wave guides

1 and 2 at the place of greatest magnetic intensity. Moreover, the Wave impedance of the slot 4 shall for good matching of the wave guide junction correspond to the geometric mean of the wave impedances of the two wave guides.

In the transmission systems according to FIGS. 1 to 4,

there is the danger that marginal currents flowing in the margin of the coupling opening causes losses and therewith an impermissible heating of the metallization of the dielectric with which the dielectric is soldered in the junction between the two wave guides. In order to avoid this danger, the dielectric is not directly inserted in the coupling opening, but the dielectric window is instead advantageously arranged in the space between the overlapping wall parts of the two wave guides. FIG. 5 shows a corresponding arrangement in sectional view, FIGS. 6 and 7 show, as noted before, respectively sections along the lines E-F and 6-H in FIG. 5.

As will be seen from these figures, there is provided in the respective mutually overlapping wall parts of the wave guides 1 and 2, an

arcuate coupling slot

4, 4, which is interrupted once in the range of the longitudinal symmetry plane of the two wave guides 1 and 2 in a similar manner as in FIGS. 1 and 2. The two coupling slots 4 and 4' are as shown in FIGS. 6 and 7 mutually displaced by Between the two coupling slots 4 and 4' is disposed the dielectric window 8 which is in the form of a ceramic disk soldered into a cylindrical metal ring 9 which interconnects the two wave guides. The cylindrical ring 9 shall be dimensioned so that the load fiux passes directly from the coupling slot 4 to the other coupling slot 4. This can be achieved by appropriate dimensioning of the impedance of the junction member which is formed by the cylindrical metal ring 9. A triggering of this junction member can also be prevented when the inhert resonance thereof lies outside of the pass range of the transmission system. If no independent oscillation can form within the metal ring 9, there will not appear any electric field components perpendicularly to the surface of the window and therewith no Wall currents.

It is not necessary that there is in a transmission system a coupling slot on each side of the window as shown in FIGS. 5-7. It will be sufiicient to provide merely in one of the two wave guides a coupling slot according to the invention, while the other wave guide is provided with a circular hole formed therein which borders on the window, as shown in FIG. 8. The dielectric Window 8 borders in such arrangement respectively directly on the coupling slot 4 and on the hole 10. The coupling slot 4 is advantageously arranged on the vacuum side of the window 8.

FIG. 9 shows an embodiment of the invention which corresponds substantially to the transmission system indicated in FIG. 8 and enables a particularly simple assembly of the system. The opening 10 in the wave guide 2 is in this case so dimensioned that its diameter is equal to the diameter of the copper ring 9 in which is inserted the window -8. The wave guide 2 can be simply placed upon the ring 9 which is with the window 8 disposed on the wave guide 1 above the coupling slot 4.

It may be mentioned at this point that the wave guides 1 and 2 which are disposed in the arrangement according to FIGS. 19 in parallel planes, can also be arranged so as to extend perpendicularly to one another, as incheated in FIGS. 10 and 11, wherein 'FIG. 10 shows the two wave guides from the top while FIG. 11 shows a side view thereof.

The invention is not inherently limited to the described and illustrated embodiments. It is, for example, not necessary that the wave guides, which are mutually closed by the vacuum-tight window, extend in parallel one with respect to the other. The coupling slot provided according to the invention, may also be situated in a partition wall extending perpendicularly to the axis of the wave guides and terminating one wave guide. The coupling slot extends in such a case along the margin of the partition wall and is interrupted in the region of the narrow side f the rectangular wave guide. Experiments have revealed that a good matching extending to the load can in such case likewise be obtained over an extraordinarily broad frequency band. It may also be mentioned that the coupling slot provided according to the invention may be interrupted several times. It is thereby merely important that the individual coupling slots are by their own scattering fields mutually coupled in such a manner that they constitute a slot line (line length greater than half the average operating wave length). It is also feasible to use circular instead of rectangular wave guides. The basic disadvantage of circular wave guides which resides in that the wave field is not definite, can be remedied by the provision of protuberances, slots or the like, formed therein.

Changes may be made within the scope and spirit of the appended claims which define what is believed to be new and desired to have protected by Letters Patent.

We claim:

1. A transmission system for electromagnetic ultra high frequency waves, especially for use in connection with high capacity ultra high frequency tubes, including two wave guides which are mutually connected by way of at least one slot-like coupling opening which is closed vacuum-tight by a dielectric window and through which the electromagnetic wave energy passes from one to the other wave guide, thereby characterized that the coupling opening extends arcuately in slot-like manner preponderantly outside a region of strong electric fields of the ultra high frequency oscillations which are present in the two wave guides, and which partially embraces such region, the total length of the coupling opening exceeding half the average operating wave length of the transmission system.

2. A transmission system according to claim 1, wherein said wave guides are substantially identically dimensioned cross-sectionally rectangular wave guides which conduct an TE -wave.

3. A transmission system according to claim 2, wherein said wave guides extend parallel to one another, mutually staggered and with the broad sides in overlapping relationship, said coupling slot being arranged in the region of the overlap of said wave guides.

4. A transmission system according to claim 2, wherein said wave guides extend in two parallel mutually perpendicularly crossing planes with one wave guide in overlapping relationship with respect to the other wave guide, said coupling slot being arranged in the region of the overlap of said wave guides.

5. A transmission system according to claim 2, wherein said wave guides extend parallel to one another, mutually staggered and with the broad sides in overlapping relationship, said coupling slot being arranged in the region of the overlap of said wave guides and being of a configuration approximating the shape of a magnetic field line which is present in the two wave guides at the place of great magnetic field intensity at average operating wavelength.

6. A transmission system according to claim 5, said wave guides being disposed directly contiguous with one wall common to both wave guides, a circular opening being formed in said common wall in which is disposed a ceramic disk carrying a metallization on each side thereof so as to form a circular marginally extending window.

7. A transmission system according to claim 5, said coupling slot being interrupted once in the region of the longitudinal symmetry plane of the two wave guides.

3. A transmission system according to claim 2, wherein said wave guides extend in two parallel mutually perpendicularly crossing planes wit-h one wave guide in overlapping relationship with respect to the other wave guide, said coupling slot being arranged in the region of the overlap of said wave guides and being of a configuration approximating the shape of a magnetic field line which is present in the two wave guides at the place of great mganetic field intensity at average operating wave length.

9. A transmission system according to claim 8, said 6 wave guides being disposed directly contiguous with one wall common to both wave guides, a circular opening being formed in said common wall in which is disposed a ceramic disk carrying a metallization on each side thereof so as to form a circular marginally extending window.

10. A transmission system according to claim 8, said coupling slot being interrupted once in the region of the longitudinal symmetry plane of the two Wave guides.

11. A transmission system according to claim 2, wherein said wave guides extend parallel to one another, mutually staggered and with the broad sides in overlapping relationship, said coupling slot being arranged in the region of the overlap of said wave guides and being of a configuration approximating the shape of a magnetic field line which is present in the two wave guides at the place of great magnetic field intensity at average operating wave length, said window being inserted directly in said coupling slot.

12. A transmission system according to claim 2, wherein said wave guides extend in two parallel mutually perpendicularly crossing planes with one wave guide in overlapping relationship with respect to the other wave guide, said coupling slot being arranged in the region of the overlap of said Wave guides and being of a configuration approximating the shape of a magnetic field line which is present in the two wave guides at the place of great magnetic field intensity at average operating wave length, said window being inserted directly in said coupling slot.

13. A transmission system according to claim 2, wherein said wave guides extend parallel to one another, mutually staggered and with the broad sides in overlapping relationship, said coupling slot being arranged in the region of the overlap of said wave guides and being of a configuration approximating the shape of a magnetic field line which is present in the two wave guides at the place of great magnetic field intensity at average operating wave length, said window being in the form of a disk made of dielectric material inserted within a cylindrical ring-shaped member and disposed in the space between the overlapping wall portions of the two wave guides and mutually interconnecting said wave guides.

14. A transmission system according to claim 13, wherein said window borders directly on the coupling slot.

15. A transmission system according to claim 14, wherein a coupling slot is formed in each of the overlapping walls of the two wave guides, said slots being mutually displaced by 16. A transmission system according to claim 14, wherein only one wave guide is provide with a coupling slot which is directed toward the window while the other wave guide is provided with a circular opening formed therein which faces said window.

17. A transmission system according to claim 13, wherein a coupling slot is formed in each of the overlapping walls of the two wave guides, said slots being mutually displaced by 180.

18. A transmission system according to claim 13, wherein only one wave guide is provided with a coupling slot which is directed toward the window while the other wave guide is provided with a circular opening formed therein which faces said window.

19. A transmission system according to claim 18, wherein said coupling slot is formed in the Wave guide lying on the vacuum side.

20. A transmission system according to claim 19, wherein the cylindrical ring in which is inserted the window, is fitted in the opening formed in the wave guide facing away from the vacuum space.

21. A transmission system according to claim 2, wherein said wave guides extend in two parallel mutually perpendicularly crossing planes with one wave guide in overlapping relationship with respect to the other wave guide, said coupling slot being arranged in the region of the overlap of said wave guides and being of a configuration approximating the shape of a magnetic field line which is present in the two wave guides at the place of great magnetic field intensity at average operating Wave length, said window being in the form of a disk made of dielectric material inserted within a cylindrical ring-shaped member and disposed in the space between the overlapping wall portions of the two wave guides and mutulally interconnecting said wave guides.

22. A transmission system according to claim 21, Wherein said window borders directly on said coupling slot.

23. A transmission system according to claim 22, wherein a coupling slot is formed in each of the overlapping walls of the two wave guides, said slots being mutually displaced by 180.

24. A transmission system according to claim 22, wherein only one wave guide is provided with a coupling slot which is directed toward the window while the other wave guide is provided with a circular opening formed therein which faces said Window.

25. A transmission system according to claim 21, wherein a coupling slot is formed in each of the overlapping walls of the two wave guides, said slots being mutually displaced by 180".

26. A transmission system according to claim 21, wherein only one wave guide is provided with a coupling slot which is directed toward the window while the other wave guide is provided with a circular opening formed therein which faces said window.

References Cited by the Examiner UNITED STATES PATENTS 2,602,859 7/52 Moreno 333-10 HERMAN KARL SAALBACH, Primary Examiner.