CA2261583A1 - Device for tuning a microwave system - Google Patents
Device for tuning a microwave system Download PDFInfo
- Publication number
- CA2261583A1 CA2261583A1 CA002261583A CA2261583A CA2261583A1 CA 2261583 A1 CA2261583 A1 CA 2261583A1 CA 002261583 A CA002261583 A CA 002261583A CA 2261583 A CA2261583 A CA 2261583A CA 2261583 A1 CA2261583 A1 CA 2261583A1
- Authority
- CA
- Canada
- Prior art keywords
- tuning
- hollow waveguide
- magnetron
- frequency
- disk
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
- H01P5/00—Coupling devices of the waveguide type
- H01P5/04—Coupling devices of the waveguide type with variable factor of coupling
Landscapes
- Constitution Of High-Frequency Heating (AREA)
Abstract
A tuning device which allows the fast periodical frequency tuning of a microwave system with simple mechanical means consists of one or several tuning elements (2, 3) which project into a wave guide (1) and are mounted to rotate around an axis (4) perpendicular to the longitudinal axis of the wave guide.
Description
CA 02261~83 1999-01-20 _ ., _ ~ . . . . .
. ~
__ Apparatus for Tuning the Frequency of a Magnetron There are times when it is necessary to periodically tune the frequency of a microwave system incrementally. Using the tuning elements that have been referred to, the penetration depth of which can be varied, this is made possible only by using a very costly drive system. Moreover, this means that no high adjustment speeds can be achieved. A microwave system with which frequency tuning is meant to be carried out at a very small period (approximately 50 ms) is a magnetron, which is used to heat substances in a microwave oven. The lossy dielectric properties of the substances that are to be heated convert the microwave energy into heat. Since such a microwave oven is a resonator in which many wave modes are excitable, an electrical field configuration with locally fixed maxima and minima is formed when the resonator is excited with a specific frequency.
The resulting thermal energy conforms to this field image and forms locally fixed hot and cold areas. Thus, it is impossibl~
to achieve even heating of the substance in the microwave oven.
This disadvantage can be avoided in that the frequency of the magnetron is varied. As the frequency changes, so does the configuration of the field within the oven, i.e., the hot and cold areas shift. This makes more even heat distribution within CA 02261~83 1999-01-20 the oven possible. The frequency of the magnetron is best tuned periodically, with a period duration of the frequency tuning of approximately 50 ms being desirable.
EP O 344 438 describes a microwave oven to which the electromagnetic field generated by a magnetron is connected through a hollow waveguide. In order to arrive at the most even possible distribution of energy density within the oven, a so-called field agitator is arranged within the hollow waveguide.
This agitator is arranged relative to the connection opening in the hollow waveguide and in the oven so that it affects the field that is introduced into the oven in such a way that even distribution of the energy density results.
GB 681 801 A and DE 10 02 053 C describe hollow waveguide tuning devices in the form of disks that incorporate an eccentric 1() stub and are supported within the wall of the hollow waveguide so as to be rotatable.
It is the objective of the present invention to describe an apparatus that requires the least costly mechanical drive syst~m in order to complete incremental frequency tuning of a magnetron l~ that changes very rapidly on a periodic basis.
According to the present invention, this objective has been achieved by the features set out in Patent Claim 1. According to this, the penetration depth of one or more tuning elements is not T ~-CA 02261~83 1999-01-20 changed for incremental frequency tuning; rather, the location of the tuning element(s) is changed by rotating them about an axis that is perpendicular to the longitudinal axis of a hollow waveguide that is connected to the magnetron. Such rotation can be executed are very high speed, with very little wear, by a simple motor drive.
As set out in the secondary claims, it is advantageous to arrange the tuning elements on one or a plurality of rotatable disks. In order to avoid interruption of the hollow waveguide wall currents to the rotating disks, it is expedient to arrange a choke connection between the disks and the walls of the hollow waveguide.
The present invention will be described in greater detail on the basis of several exemplary embodiments shown in the drawings l~ appended hereto. These drawings show the following:
Figure 1: a longitudinal cross section through a hollow waveguide with a rotatable tuning device;
Figure 2: a plan view of this hollow waveguide, in direction A;
~~ Figure 3: a longitudinal cross section through a hollow waveguide with a rotatable inductive loop;
Figure 4: A Rike diagram.
CA 0226l~83 l999-0l-20 Figure 1 shows a longitudinal cross section through a hollow waveguide 1 that is connected, for example, to a magnetron 11 in order to tune the frequency of this periodically. To this end, within the hollow waveguide 1 there are two stubs 2 and 3 as tuning elements, and these are supported so as to be able to rotate about a axis 4 that is oriented so as to be perpendicular to the longitudinal axis of the hollow waveguide. By rotating the stubs 2 and 3, which are spaced apart from the axis of rotation by a distance that is approximately one-quarter the lo wavelength of the hollow waveguide, their phase effect is changed from capacitive to inductive. In addition, as well as the phase, the amount of the reflection factor also changes, since the distance of the stubs 2 and 3 from the centre of the waveguide also changes.
1~ Unlike the embodiment shown in Figure 1, instead of the two stubs 2 and 3 it is possible to rotate either a single stub or more than two stubs. In the same way, as is shown in Figure 3, in place of capacitive stubs, one or a plurality of inductive loops 5 can be rotated about the axis 4 within the hollow 2~ waveguide 1. The number of tuning elements, the type of these (stubs or loops) and their distance from the axis of rotation will be determined according to which variation of the phase and the amount of the reflection factor that is to be achieved.
CA 02261~83 1999-01-20 One or more fixed tuning elements 6 can also be installed in the hollow waveguide in addition to the rotatable tuning elements. Because of the interaction of the rotating tuning element(s) 2,3,5 relative to the fixed tuning element(s) 6, the total reflection factor traces a curve in the Smith diagram that can be approximated to a desired curve by suitable dimensioning of the tuning elements and by their spacing relative to each other.
As can be seen from the longitudinal cross sections through the hollow waveguide l shown in Figures 1 and 3 and the plan view of the hollow waveguide, in direction A, shown in Figure 2, the tuning elements 2,3,5 are arranged on a circular disk 7 that is supported so as to be able to rotate within the hollow waveguide wall. The disk 7 is mounted on a drive shaft 8 l~ by which the disk 7 can be rotated by means of a motor. The disk 7 is supported in such a way in an opening in a wall of the hollow waveguide that it is free of contact. In order to avoid interruption of the hollow waveguide wall currents to the rotating disk 7, a collar 9 is installed on the wall of the hollow waveguide at the edge of the opening, and in the same way, a collar 10 is installed on the edge of the disk 7. Both collars g and 10 are of a height that is approximately that of one-quarter of the wavelength ~ and form a choke, i.e., the open CA 02261~83 1999-01-20 circuit at the upper end of the gap between the two collars 9 and 10 is transformed into a short circuit at the lower end (in the wall of the hollow waveguide).
A plurality of rotating disks with one or more tuning S elements can also be used in the hollow waveguide.
As has already been discussed, the tuning device that has been described can be connected to a magnetron 11 in order to adjust its frequency on a periodic basis. In order to tune the frequency of a magnetron it is possible to use the fact that the frequency and the output power of a magnetron are dependent on the value of the load resistance, which can be adjusted by means of the tuning device. This dependency is illustrated in the Rike diagram that is shown in Figure 4. The Rike diagram shows the frequency and power behaviour of a magnetron that is connected to 1~ different load resistances of various reflection factors. On connection with the characteristic impedance (mid-point of the diagram), the maximum power (> 12kW) will be at the frequency f0.
The constant-power curves are arranged elliptically around the~
mid-point. The dashed lines are constant-frequency curves. The 2() hashed area represents the prohibited zone. If the magnetron is operated with reflection factors within this prohibited zone, mode shifts that could result is its destruction may occur within the magnetron. If a magnetron is to be tuned periodically over a CA 02261~83 1999-01-20 wide range of frequencies, without any notable loss of output power, the reflection factor of the terminal resistance can-, for example, conform to the power curve for 11.5 kW, from the left-hand limit of the prohibited zone as far as the right-hand limit, along the constant-power curve and back.
. ~
__ Apparatus for Tuning the Frequency of a Magnetron There are times when it is necessary to periodically tune the frequency of a microwave system incrementally. Using the tuning elements that have been referred to, the penetration depth of which can be varied, this is made possible only by using a very costly drive system. Moreover, this means that no high adjustment speeds can be achieved. A microwave system with which frequency tuning is meant to be carried out at a very small period (approximately 50 ms) is a magnetron, which is used to heat substances in a microwave oven. The lossy dielectric properties of the substances that are to be heated convert the microwave energy into heat. Since such a microwave oven is a resonator in which many wave modes are excitable, an electrical field configuration with locally fixed maxima and minima is formed when the resonator is excited with a specific frequency.
The resulting thermal energy conforms to this field image and forms locally fixed hot and cold areas. Thus, it is impossibl~
to achieve even heating of the substance in the microwave oven.
This disadvantage can be avoided in that the frequency of the magnetron is varied. As the frequency changes, so does the configuration of the field within the oven, i.e., the hot and cold areas shift. This makes more even heat distribution within CA 02261~83 1999-01-20 the oven possible. The frequency of the magnetron is best tuned periodically, with a period duration of the frequency tuning of approximately 50 ms being desirable.
EP O 344 438 describes a microwave oven to which the electromagnetic field generated by a magnetron is connected through a hollow waveguide. In order to arrive at the most even possible distribution of energy density within the oven, a so-called field agitator is arranged within the hollow waveguide.
This agitator is arranged relative to the connection opening in the hollow waveguide and in the oven so that it affects the field that is introduced into the oven in such a way that even distribution of the energy density results.
GB 681 801 A and DE 10 02 053 C describe hollow waveguide tuning devices in the form of disks that incorporate an eccentric 1() stub and are supported within the wall of the hollow waveguide so as to be rotatable.
It is the objective of the present invention to describe an apparatus that requires the least costly mechanical drive syst~m in order to complete incremental frequency tuning of a magnetron l~ that changes very rapidly on a periodic basis.
According to the present invention, this objective has been achieved by the features set out in Patent Claim 1. According to this, the penetration depth of one or more tuning elements is not T ~-CA 02261~83 1999-01-20 changed for incremental frequency tuning; rather, the location of the tuning element(s) is changed by rotating them about an axis that is perpendicular to the longitudinal axis of a hollow waveguide that is connected to the magnetron. Such rotation can be executed are very high speed, with very little wear, by a simple motor drive.
As set out in the secondary claims, it is advantageous to arrange the tuning elements on one or a plurality of rotatable disks. In order to avoid interruption of the hollow waveguide wall currents to the rotating disks, it is expedient to arrange a choke connection between the disks and the walls of the hollow waveguide.
The present invention will be described in greater detail on the basis of several exemplary embodiments shown in the drawings l~ appended hereto. These drawings show the following:
Figure 1: a longitudinal cross section through a hollow waveguide with a rotatable tuning device;
Figure 2: a plan view of this hollow waveguide, in direction A;
~~ Figure 3: a longitudinal cross section through a hollow waveguide with a rotatable inductive loop;
Figure 4: A Rike diagram.
CA 0226l~83 l999-0l-20 Figure 1 shows a longitudinal cross section through a hollow waveguide 1 that is connected, for example, to a magnetron 11 in order to tune the frequency of this periodically. To this end, within the hollow waveguide 1 there are two stubs 2 and 3 as tuning elements, and these are supported so as to be able to rotate about a axis 4 that is oriented so as to be perpendicular to the longitudinal axis of the hollow waveguide. By rotating the stubs 2 and 3, which are spaced apart from the axis of rotation by a distance that is approximately one-quarter the lo wavelength of the hollow waveguide, their phase effect is changed from capacitive to inductive. In addition, as well as the phase, the amount of the reflection factor also changes, since the distance of the stubs 2 and 3 from the centre of the waveguide also changes.
1~ Unlike the embodiment shown in Figure 1, instead of the two stubs 2 and 3 it is possible to rotate either a single stub or more than two stubs. In the same way, as is shown in Figure 3, in place of capacitive stubs, one or a plurality of inductive loops 5 can be rotated about the axis 4 within the hollow 2~ waveguide 1. The number of tuning elements, the type of these (stubs or loops) and their distance from the axis of rotation will be determined according to which variation of the phase and the amount of the reflection factor that is to be achieved.
CA 02261~83 1999-01-20 One or more fixed tuning elements 6 can also be installed in the hollow waveguide in addition to the rotatable tuning elements. Because of the interaction of the rotating tuning element(s) 2,3,5 relative to the fixed tuning element(s) 6, the total reflection factor traces a curve in the Smith diagram that can be approximated to a desired curve by suitable dimensioning of the tuning elements and by their spacing relative to each other.
As can be seen from the longitudinal cross sections through the hollow waveguide l shown in Figures 1 and 3 and the plan view of the hollow waveguide, in direction A, shown in Figure 2, the tuning elements 2,3,5 are arranged on a circular disk 7 that is supported so as to be able to rotate within the hollow waveguide wall. The disk 7 is mounted on a drive shaft 8 l~ by which the disk 7 can be rotated by means of a motor. The disk 7 is supported in such a way in an opening in a wall of the hollow waveguide that it is free of contact. In order to avoid interruption of the hollow waveguide wall currents to the rotating disk 7, a collar 9 is installed on the wall of the hollow waveguide at the edge of the opening, and in the same way, a collar 10 is installed on the edge of the disk 7. Both collars g and 10 are of a height that is approximately that of one-quarter of the wavelength ~ and form a choke, i.e., the open CA 02261~83 1999-01-20 circuit at the upper end of the gap between the two collars 9 and 10 is transformed into a short circuit at the lower end (in the wall of the hollow waveguide).
A plurality of rotating disks with one or more tuning S elements can also be used in the hollow waveguide.
As has already been discussed, the tuning device that has been described can be connected to a magnetron 11 in order to adjust its frequency on a periodic basis. In order to tune the frequency of a magnetron it is possible to use the fact that the frequency and the output power of a magnetron are dependent on the value of the load resistance, which can be adjusted by means of the tuning device. This dependency is illustrated in the Rike diagram that is shown in Figure 4. The Rike diagram shows the frequency and power behaviour of a magnetron that is connected to 1~ different load resistances of various reflection factors. On connection with the characteristic impedance (mid-point of the diagram), the maximum power (> 12kW) will be at the frequency f0.
The constant-power curves are arranged elliptically around the~
mid-point. The dashed lines are constant-frequency curves. The 2() hashed area represents the prohibited zone. If the magnetron is operated with reflection factors within this prohibited zone, mode shifts that could result is its destruction may occur within the magnetron. If a magnetron is to be tuned periodically over a CA 02261~83 1999-01-20 wide range of frequencies, without any notable loss of output power, the reflection factor of the terminal resistance can-, for example, conform to the power curve for 11.5 kW, from the left-hand limit of the prohibited zone as far as the right-hand limit, along the constant-power curve and back.
Claims (5)
1. An apparatus for tuning the frequency of a magnetron, characterized in that at least one tuning element (2,3), which acts inductively or capacitively, is so arranged in a hollow waveguide (1) that is connected to the magnetron (11) that it affects the frequency of the magnetron (11); and in that at least one tuning element (2,3) is supported so as to be rotatable about an axis (4) that is oriented so as to be perpendicular to the longitudinal axis of the hollow waveguide, so that incremental frequency tuning of the magnetron (11) results.
2. An apparatus as defined in Claim 1, characterized in that one or a plurality of tuning elements (2,3,5) are arranged on a disk (7) that is supported so as to be rotatable in a wall of the hollow waveguide.
3. An apparatus as defined in Claim 1 or Claim 2, characterized in that a plurality of disks with tuning elements are supported so as to be rotatable within one or more of the walls of the hollow waveguide.
4. An apparatus as defined in Claim 2 or Claim 3, characterized in that an annular collar (10) on the disk (7) and an annular collar (9) that is mounted on the wall of the hollow waveguide and encircles the disk (7) form a choke; and in that both collars (9,10) are of a height that is approximately equal to one-quarter the wavelength of the hollow waveguide.
5. An apparatus as defined in one of the preceding claims, characterized in that apart from the rotatably supported tuning element(s) (2,3,5) at least one fixed tuning element (6) extends into the hollow waveguide (1)
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19629864 | 1996-07-24 | ||
| DE19629864.4 | 1996-07-24 | ||
| DE19634416.6 | 1996-08-26 | ||
| DE19634416A DE19634416A1 (en) | 1996-07-24 | 1996-08-26 | Device for tuning a microwave arrangement |
| PCT/DE1997/001463 WO1998005086A1 (en) | 1996-07-24 | 1997-07-07 | Device for tuning a microwave system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2261583A1 true CA2261583A1 (en) | 1998-02-05 |
Family
ID=26027781
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002261583A Abandoned CA2261583A1 (en) | 1996-07-24 | 1997-07-07 | Device for tuning a microwave system |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0913011A1 (en) |
| JP (1) | JP2000515348A (en) |
| CA (1) | CA2261583A1 (en) |
| WO (1) | WO1998005086A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1700610B1 (en) * | 2000-09-22 | 2020-04-01 | Environmental Waste International Inc. | Magnetron assembly |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB681801A (en) * | 1951-08-03 | 1952-10-29 | Standard Telephones Cables Ltd | Improvements in or relating to matching arrangements for electromagnetic waveguides |
| FR1069351A (en) * | 1952-01-01 | 1954-07-07 | Int Standard Electric Corp | Improvements to the elements making up the waveguides |
| DE1002053B (en) * | 1955-08-06 | 1957-02-07 | Siemens Ag | Arrangement for achieving an adjustable transformation in waveguides |
| US2910659A (en) * | 1956-05-21 | 1959-10-27 | Bell Telephone Labor Inc | Microwave impedance branch |
| US2863128A (en) * | 1956-09-19 | 1958-12-02 | Gen Precision Lab Inc | Waveguide tuner |
| FR2583597A1 (en) * | 1985-06-13 | 1986-12-19 | Alcatel Thomson Faisceaux | HYPERFREQUENCY PASSPORT FILTER IN EVANESCENT MODE |
| DE3818490A1 (en) * | 1988-05-31 | 1989-12-07 | Bosch Siemens Hausgeraete | MICROWAVE HOUSEHOLD APPLIANCE |
-
1997
- 1997-07-07 EP EP97933626A patent/EP0913011A1/en not_active Withdrawn
- 1997-07-07 CA CA002261583A patent/CA2261583A1/en not_active Abandoned
- 1997-07-07 JP JP10508370A patent/JP2000515348A/en active Pending
- 1997-07-07 WO PCT/DE1997/001463 patent/WO1998005086A1/en not_active Application Discontinuation
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1700610B1 (en) * | 2000-09-22 | 2020-04-01 | Environmental Waste International Inc. | Magnetron assembly |
Also Published As
| Publication number | Publication date |
|---|---|
| JP2000515348A (en) | 2000-11-14 |
| EP0913011A1 (en) | 1999-05-06 |
| WO1998005086A1 (en) | 1998-02-05 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |