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Publication numberUS2679595 A
Publication typeGrant
Publication dateMay 25, 1954
Filing dateNov 18, 1950
Priority dateNov 18, 1950
Publication numberUS 2679595 A, US 2679595A, US-A-2679595, US2679595 A, US2679595A
InventorsSpencer Percy L
Original AssigneeRaytheon Mfg Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
High-frequency protective circuits
US 2679595 A
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Description  (OCR text may contain errors)

May 25, 1954 P. L. SPENCER HIGH-FREQUENCY PR OTECTIVE CIRCUITS Filed Nov. 18, 1950 wdwh Patented May 25, 1954 UNITED STATES PATENT OFFICE HIGH-FREQUENCY PROTECTIVE CIRCUITS .Percy L. Spencer, West Newton, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application November 18, 1950, Serial No. 196,434

8 Claims. 1

This invention relates to electrical circuits, and more particularly to a system for automatic pro tection of a microwave oscillator producing continuous waves.

In electron tubes used to produce microwave energy such as magnetrons, for greatest elliciency the device should work into a load of op timum value. When this is the case, the voltage standing wave ratio in the transmission line connecting the tube and the load will be found to be unity. When this is not the case, the ratio will be at some higher value. Thus the voltage standing wave ratio may be taken as an indication of match or mismatch of the load and generator. As the standing wave is created by the presence of reflected energy'in the transmission line, a device, such as a directive coupler adapted to transmit energy in one direction only and terminated in a detector, can be used to detect the presence of standing waves in the transmission line.

The effect of reflected energy on the magnetron is to bombard the cathode with electrons and heat it. If this condition is not corrected prompt- 1y, serious damage may be done to the tube. Further increase in temperature of the cathode may be prevented if the filament voltage is promptly reduced.

It is the purpose of the present invention to provide means for sensing an increase in the refiected power and in response reduce the filament power. This is done by inserting a directive coupling in the transmission line and deriving from it a control voltage that in turn controls the current through a saturating winding on the filament transformer supplying filament power to the magnetron.

Such a control system automatically maintains the cathode of the tube at the optimum temperature in spite of considerable variation in load conditions. Thus the cathodes and other structures of the tube are not exposed to excessive heat for any appreciable length of time, thus prolonging the life of these relatively expensive tubes. Other automatic control devices for micro-wave tubes, such as that disclosed in Patent No. 2,498,719, depend upon critical spacing of one or more probes within the transmission line from generator to load. The present device is independent of the phase of the standing wave and so does not have to be positioned at any particular point in the transmission line.

These features make the device particularly useful in industrial application of microwave energy where the energy is used to heat various substances presenting various loads to the generator. It is also useful in unattended microwave communication links, such as television relays where the load conditions may change suddenly in the absence of a skilled operator.

Other and further advantages of this invention will be apparent as the description thereof progresses, reference being had to the accompanying drawing, wherein the single figure is a diagrammatic representation of a protective system according to this invention.

Now referring to the drawing, the numeral I0 refers generally to the magnetron generating microwave energy that is picked up by the an.- tenna probe I I and introduced into a wave guide I2. At a convenient distance a loop I3, of the type described by H. C. Early in the November, 1946, Proceedings of the Institute of Radio Engineers at page 883 and shown schematically in Fig. 1 of that article, and in greater detail in Figs. 6 and '7, is inserted into the wave guide I2 through a slot I4. One side of the loop may be connected through a coaxial cable I5 to an incident power indicator, not shown as it is no part of the present invention. The far side of the loop is connected through a length of coaxial cable I!) to a crystal rectifier [6 that is connected to ground through a resistor I1. The crystal I6 is connected in such polarity that, as the reflected power picked up by the loop I3 becomes greater, the junction point I8 becomes increasingly negative. The point I8 is connected to an amplifier 20 which may be of any conventional design adapted to amplify a slowly varying D. C. potential. The input should be of high impedance and the output of low impedance. This output is connected in series to a saturating winding 2| on the core 22 of a filament transformer 23. The primary 24 of this transformer is connected to a source of A. C. power 25. The secondary 26 is connected to the filament 2'! of the magnetron I0.

When the magnetron I0 is operating normally into a matched. load, the voltage standing wave ratio will be unity and there will be no reflected power to be picked up by the loop I3 and detected by crystal IS. The amplifier 20 passes a normal amount of current through the winding 2| leaving the core 22 unsaturated and permitted the magnetron filament 21 to receive its normal amount of energy.

When the load changes to create a mismatch and cause reflected energy to be picked up by the loop I3 and detected by the crystal I6, the flow of current through the saturating winding 2| increases to saturate the core 22 of the filament transformer 23. This reduces the amount of power transferred to the secondary 26 and delivered to the filament 21 of the magnetron, thus reducing the temperature of its cathode.

When the load conditions return to normal, the standing wave ratio in th transmission line i2 returns to unity and there is no reflected energy to be detected and no signal at the input of the amplifier 20. This reduces the flow of current through the saturating winding 2| on the core 22 of the transformer 23 permitting full heater energy to pass to the filament 21 of the magnetron in increasing its temperature, thus maintaining the cathode of the magnetron H3 at a constant temperature under a wide range of load conditions.

Any type of directional coupler could be used in place of the loop l3 shown. Also any con venient type of rectifier could be used in place of the crystal type I6 shown.

This invention is not limited to the particular details of construction and materials described, as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

l. A protective system comprising a source of radio frequency energy, a heater for said source, means for delivering energy to said heater, a transmission line for coupling said source to a load, means for detecting reflected energy in said transmission line, and means for varying the energy delivered to said heater in response to the output of the detecting means.

2. A protective system comprising a source of radio frequency energy, a heater for said source, means for delivering energy to said heater, comprising a transformer with a core and a saturating winding on said core, a transmission line for coupling said source to a load, means for detecting reflected energy in said transmission line, and means for varying the energy delivered to said heater in response to the output of the detecting means, comprising a saturable core reactance in said means for delivering energy to said heater.

3. A protective system comprising a source of radio frequency energy, a heater for said source,

means for delivering energy to. said heater, comprising a transformer with a core and a saturating winding on said core, a transmission line for coupling said source to a load, means for detecting reflected energy in said transmission line,

and means for varying the energy delivered to a said heater in response to the output of the detecting means, comprising means for coupling the output of said detector to the said saturating Winding.

4. A protective system comprising a source of radio frequency energy, a heater for said source, means for delivering energy to said heater, a transmission line for coupling said source to a load, means for detecting reflected energy in said transmission line, said means comprising a rectifier coupled to said transmission line through a directional coupling means, and means for varying the energy delivered to said heater in response to the output of the detecting means.

5. A protective system comprising a source of radio frequency energy, a heater for said source, means for delivering energy to said heater, comprising a transformer with a core and a saturating winding on said core, a transmission line for coupling said source to a load, means for detecting reflected energy in said transmission line, said means comprising a rectifier coupled to said transmission line through a directional coupling means, and means for varying the energy delivered to said heater in response to the output of the detecting means, comprising a saturable core reactance in said means for delivering energy to heater.

6. A protective system comprising a source of radio frequency energy, a heater for said source, means for delivering energy to said heater, comprising a transformer with a core and a saturating winding on said core, a transmission line for coupling said source to a load, means for detect- 25 ing reflected energy in said transmission line, said means comprising a rectifier coupled to said transmission line through a directional coupling means, and means for varying the energy delivered to said heater in response to the output of .0 the detecting means, comprising means for coupling the output of said detector to the said saturating Winding.

'7. A protective system comprising a source of radio frequency energy, an energy control for 35 said source, means for delivering energy to said energy control, a transmission line coupling said source to a load, an alternating current directional coupler connected to said transmission line for detecting substantially only reflected energy 4.0 in said transmission line, and means for varying said energy control in response to the output of said detecting means.

8. A protective system comprising a source of radio frequency energy, an energy control for said source comprising a saturable core reactance, means for delivering energy to said energy control, a transmission line coupling said source to a load, an alternating current directional coupler connected to said transmissionline for detecting substantially only reflected energy in said transmission line, and means for varying said energy control in response to the output of said detecting means.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,930,545 Wensley Oct. 17, 1933 2,149,080 Wolff Feb. 28, 1939 2,175,694 Jones Oct. 10, 1939 2,236,195 McKesson Mar. 25, 1941 2,262,044 Philpott Nov. 11, 1941 2,386,040 Edwards Oct. 2, 1945 2,408,091 Olesen Sept. 24, 1946

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US1930545 *Nov 13, 1929Oct 17, 1933Westinghouse Electric & Mfg CoCurrent-controlling apparatus
US2149080 *Nov 28, 1936Feb 28, 1939Rca CorpCurrent or voltage regulator
US2175694 *Jul 30, 1938Oct 10, 1939Rca CorpOscillator
US2236195 *Dec 15, 1938Mar 25, 1941Rca CorpAutomatic cathode voltage adjusting device
US2262044 *Mar 2, 1938Nov 11, 1941Philpott La Verne RTemperature control for magnetron filament
US2386040 *Sep 28, 1942Oct 2, 1945Gen ElectricElectric control system
US2408091 *May 19, 1944Sep 24, 1946Cons Eng CorpElectrical regulating system
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3069624 *Mar 14, 1961Dec 18, 1962David S FriedmanAutomatic power trip switch for a transmitter having high reflective power
US4196332 *May 1, 1978Apr 1, 1980Canadian Patents And Development LimitedControlled heating microwave ovens
US4449043 *Oct 30, 1981May 15, 1984The United States Of America As Represented By The Secretary Of The Air ForceOptical power source control system
US4757171 *Jun 30, 1987Jul 12, 1988Litton Systems, Inc.Continuous transformer and motor
US4801775 *Feb 1, 1988Jan 31, 1989Microwave Products Of America, Inc.Shading band compensation for continuous transformer and motor
US4801776 *Feb 1, 1988Jan 31, 1989Microwave Products Of America, Inc.Flux reduction compensation for continuous transformer and motor
US4812607 *Sep 2, 1987Mar 14, 1989Microwave Products Of America, Inc.Compensation for improved continuous transformer and motor
US4827097 *May 7, 1986May 2, 1989Litton Systems, Inc.Continuous transformer and motor
US6850010Jul 16, 2003Feb 1, 2005Fusion Uv Systems, Inc.Microwave powered lamp with reliable detection of burned out light bulbs
EP1499164A2 *Jul 16, 2004Jan 19, 2005Fusion Uv Systems, Inc.Microwave powered lamp with reliable detection of burned out light bulbs
Classifications
U.S. Classification331/62, 331/88, 219/737
International ClassificationH03F1/54, H03F1/52, H05B6/66
Cooperative ClassificationH03F1/544, H05B6/666
European ClassificationH05B6/66S, H03F1/54C