US 3705364 A
Description (OCR text may contain errors)
United States Patent Takeshima 1 Dec. 5, 1972 1541 APPARATUS FOR GENERATING 3,465,265 9/1969 1mm ..332/30 v MICROWAVES HAVING A 3,524,149 8/1970 Socci ..332/16 1 GENERATING ELEMENT AND OTHER PUBLICATIONS VARIABLE REACTANCE ELEMENT IN A CAVITY RESONATOR, Fenner, Internal Frequency Modulation of GaAs Junction L se s b1 qa'nalhelnskx9Bfr ti  Inventor: Masumi Takeshlma, Takatsuki-shi, b 'g' Injection 15 1964, vol. 5
Japan No. 10, pp. l98-l99 1 Fleming Electronic FM Modulation of GaAs Osc.
M h E t C t  Assgnee 'fig gg V01. 8, NO. 8, Jan. 1966 p. 1077 IBM TechJDisclosure Bulletin  Filed: Sept 29, 1969 Eastman, Gunn Effect with Control Electrode" R.C.A. Tech. Notes 756, Apr. 1968 ] L671 Standley et 61., ASO-GHz lMPA'I'I Diode Osc. &
' Amppp. 741-747 Oct. 1968  Foreign Application Priority Data Primary Examiner-Alfred L. Brody Oct. 4, Japan At t0rney Stevens, Davis Miller & Masher  US. Cl. ..332/18, 307/303, 307/307, 57 ABSTRACT 307/320,331/l07 R, 331/107 G,332/30V 1  Int. Cl. ..H03c 3/08 Apparatus mlcl'owaves p a  Field of Search; ..332/18, 30, 30 V; 307/299, cavity resonator microwave generating element and 307/303 320 331/107 R"1O7 G, 107 S, a solid-state variable reactance element such as a vari- 107 T, 107 A; 317/234 able capacitance diode, both of these elements being disposed within the cavity resonator. It is possible to  References Cited obtain a controlled and/or a modulated microwave 1 output from the apparatus by varying the reactance of UNITED STATES PATENTS and/or by supplying a modulating signal to the varia ble reactance element. 3,141,141 7/1964 Sharpless ..33l/l07 T 3,307,115 2/1967 Tschannen ..33 1136 C X 2 Claims, 2 Drawing Figures 9 Y 5 l l 1 0 C. MPL/F/ER POWERmI/RCE SIGNAL 4 Mr-il- SOURCE 0C POI 11:7? SOURCE IMP/l rT DIODEI VAR/1670f? APPARATUS FOR GENERATING MICROWAVES HAVING A GENERATING ELEMENT AND VARIABLE REAcTANcE ELEMENT IN A CAVITY RESONATOR I The present invention relates to apparatuses for generating microwaves, particularly to those capable of generating controlled microwave outputs. I
Heretofore, the frequency control of a generation output from a microwave generating element such as a known avalanche diode (also called an IMPATT diode, an abbreviation for Impact ionization Avalanche Transit Time diode) has been performed by mechanical means of operation. Namely, at one end of a cavity resonator into which a generating element such as men.- tioned above is incorporated, a movable short-circuiting piston is provided andthis piston is adjusted to derivea generation outputresonant with the resonator, and then the derived output is supplied through a waveguide to a load terminal section. Such way of controlling a microwave output, being mechanically carried out, has poor practicability and is troublesome to achieve fine adjustment. I
Another way of controlling the frequency and/or the amplitude of=a microwave output froma usual solidstate generating element such as an IMPATT diode conventionally employed is that an AC. or a DC control signal is applied directly to the diode thereby to vary the operating point of the diode itself for effecting the frequency modulation. In this way of modulation, however, thereexisted such a danger that the element might be led to a thermalbreakdown due to an excess power caused by a modulation signal.
An object of the present invention is to provide an apparatus for generating microwaves free from the above-mentioned drawbacks heretofore experienced.
Another object of the present invention isto provide an apparatus for generating controlled microwaves without changing the operating state of a generating element.
To this end, the apparatus of the present invention comprises a cavity resonator, a generating element disposed within the cavity resonator, a variable reactance element placed in the vicinity of the generating element within the'cavity resonator and means for applying a control signal to'the variable reactance element. The arrangement of thevariable reactance element should be such that when in the resonator the variable reactance element is on one side of the generating element on which a load exists the reactance element be within a distance from the generating element as large as two wavelengths of a microwave to be generated from the apparatus while when in the resonator the variable reactance element is on the opposite side of the generating element the reactance element be between the generating element and a short-circuiting piston. By the apparatus of the present invention, a controlled microwave output resonant with the resonator can be derived owing to the operation of the variable reactance element.
The present invention will now be described in detail referring to a preferred embodiment in conjunction with the accompanying drawings, in which: a
FIG. 1 is a block diagram illustrating an example of the apparatus for generating microwaves as well as an example of an application of the apparatus in accordance with the present invention; and
FIG. 2 is a graph showing a characteristic curve of a Variable reactance element which may be used in the apparatus shown in FIG. 1.
. Referring to FIG. 1 showing a preferred embodiment of the present invention, within a cavity resonator 1 there are disposed a microwave generating element 2, for example, an IMPATT diode and a variable reactance element 3, for example, a variable capacitance diode known as a varactor in the vicinity of the IMPATT diode 2. Separate DC. power sources 4 and 5 are provided for the IMPATT diode 2 and the variable reactance element 3 respectively. One end of the cavity resonator l is provided witha variable shortcircuiting piston 6. In operation, the short piston 6 is operated to adjust the effective cavity of the resonator 1, and by adjusting the bias voltage to be applied to the variable reactance element 3 to aproper value, the apparatus can be tuned to a desired frequency. That is, when the IMPATT diode 2 is given a bias by the DC. power source 4 and is put in a microwave generating state, a predetermined microwave is generated. The frequency of oscillation can be varied only by varying the bias voltage applied to the variable reactance element 3. Thus, in the present invention, the tuning of the cavityresonator l is electrically performed by the variable reactance element 3 though conventionally the A tuning is performed almost mechanically by the short piston 6.
The variable reactance element 3 serving as a variable reactance element may have a well-known variable capacitance characteristic depending on the voltage V applied to the pn junction of the variable reactance element 3, the change in the capacitance C of the element covering several to 10 picofarads, as shown in FIG. 2. Therefore, by incorporating the variable reactance element 3 along with the microwave generating element 2 into the resonator 1, electrical adjustment of the tuning frequency of the resonator is possible owing to the variable capacitance characteristic as shown in FIG. 2 of the element 3 in accordance with the adjustment of the DC. power source 5.
In accordance with the experiments of the present inventor, the positioning of the variable reactance element 3 with respect to the microwave generating element 2 within the cavity resonator should be such that the variable reactance element 3 is disposed within a distance as large as two wavelengths of the generated microwave from the apparatus measured from the element 2 towards the load or is disposed between the element 2 and the terminator or short piston 6. When. the positioning of the element 3 was not being such as mentioned above, the resulting microwave output was not satisfactory with the tuning sensitivity dulled while use of a single semiconductor substrate in which both of the elements 2 and 3 were formed under the so-called IC technique in an effort to realize close positioning of the elements or positioning of the element 3 at a distance three-eighths wavelengths or seven-eighths wavelengths of a generated microwave apart from the element 2 resulted in a high performance, miniaturized structure of the apparatus.
Furthermore, by superposing an A.C. signal on a proper DC. bias potential applied to the variable reactance element 3 such as a variable capacitance diode, a frequency modulation can be achieved. That is, as shown in FIG. 1, the varactor or the variable reactance element 3 is provided with a proper DC. bias by the DC. power source 5, and at the same time a modulating signal is supplied to the variable reactance element 3 from a signal source 7. As the operating point of the variable reactance element 3 is varied depending on the supplied modulating signal from the source 7, the generated output of the apparatus is frequency modulated and fed to the load. In one example of the apparatus of the present invention, use of a modulating signal at 2 MHz yielded a width of frequency modulation of about I MHz/V.
Furthermore, even if the frequency of the generated I microwave is changed by some unexpected reason, for
example, the operating condition of the IMPATT diode 2 is fluctuated by accident, such fluctuation can be automatically compensated for according to the present invention.
That is, as shown in FIG. 1, a portion of the output of the apparatus is used to detect a frequency deviation or difference of the output from the normal state and the detected frequency difference is fed to an converted into a voltage signal by a frequency discriminator 8. The output of the frequency discriminator 8 is negatively fed back to the varactor 3 through an amplifier 9. As a result, automatic frequency control of the apparatus is attained.
Although in the foregoing description of the apparatus of the present invention, reference is made to an IMPATT diode as a microwave generating element, other solid-state generating elements such as a Gunn diode, LSA diode and a tunnel diode can equally be used. As for the variable reactance element, apart from the varactor, use may be made of any semiconductor elements having characteristics similar to those of the varactor such as a usual pn junction diode, a Schottky barrier diode, an MOS type diode and a point contact diode.
As has been described above, as the apparatus for generating microwaves in accordance with the present invention comprises a cavity resonator, a generating element disposed within the cavity'resonator, a variable reactance element positioned in the vicinity of the generating element in the resonator and means for applying a control signal to the reactance element so that any output signal in the microwave range is available without varying the operating point of the generating clement itself, the generating element is operated in a desirable stabilized state and therefore any thermal breakdown of the generating element no longer occurs. The design of the apparatus is considerably facilitated. In addition, since the variable reactance element such as a variable capacitance diode has a high impedance with respect to a modulating signal source, advantageously a modulating signal may have an amplitude smaller than that used conventionally.
What is claimed is:
1. An apparatus for generating microwaves, comprising: a cavity resonator; a generating element disposed within said resonator; a load coupled with said resonator on one side thereof; a short-circuiting piston provided on the opposite side of said resonator from said load; a variable reactance element formed on a single substrate with said generating element and axially positioned in said resonator on the same side of generating element as said load, wherein the distance between said generating element and said variable reactance element is between three-eighths and seven-eighths wavelength of a microwave generated by said apparatus; means applying a control signal to said variable reactance element; means, including a frequency discriminator, for producing a signal representative of the difference between the actual output of said apparatus and a predetermined reference; means for feeding back said difference signal to said variable reactance element; and means for superimposing a modulating signal on said control signal.
2. An apparatus for generating microwaves, comprising: a cavity resonator; a generating element disposed within said resonator; a load coupled with said resonator on one side thereof; a short-circuiting piston provided on the opposite side of said resonator from said load; a variable reactance element formed on a single substrate with said generating element and axially positioned in said resonator on the opposite side of said generating element as said load, wherein the distance between said generating element and said variable reactance element is between three-eighths and seveneighths wavelength of a microwave generated by said apparatus; means applying a control signal to said variable reactance element; means, including a frequency discriminator, for producing a signal representative of the difference between the actual output of said apparatus and a predetermined reference; means for feeding back said difference signal to said variable reactance element; and means for superimposing a modulating signal on said control signal.