JPH0685542A - Variable frequency microwave oscillator - Google Patents

Abstract

PURPOSE:To provide the variable frequency microwave oscillator which is equipped with a low loss, wide variable width and stable temperature. CONSTITUTION:A microwave resonator combining a variable electrostatic capacitor 1 for changing electrostatic capacity by changing a gap (d) between two parallel metallic plates 5 and 5a with a mechanical displacing element and a low-loss inductance element 2 is combined with a negative resistance circuit. On the other hand, an electrically controllable piezoelectric element or magnetostriction element is used as the mechanical displacing element. Further, the inductance element is composed of a microstrip line.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention responds to downsizing, high frequency, and low power consumption of electronic equipment in a high frequency band, and is an important component used in these equipments. Regarding variable width and temperature stabilization.

[0002]

2. Description of the Related Art With the progress of integrated circuits, downsizing, high frequency, and low power consumption of electronic devices in the high frequency band have been rapidly progressing. Among them, it can be said that the performance improvement of the variable frequency microwave oscillator is delayed as compared with other elements. In particular,
In the 10 MHz to 5 GHz band, development of a temperature variable frequency microwave oscillator with low loss and a wide variable width is strongly desired. In order to meet these requirements, as shown in FIG. 9, a variable frequency microwave oscillator in which a variable capacitance element 1 ′ using a PN junction of a semiconductor diode and an inductance element 2 are combined is widely used. The microwave resonator in FIG. 9 shows a case where the variable capacitance element 1 ′ and the inductance element 2 are connected in parallel. Reference numeral 3 is a negative resistance circuit composed of transistors. Terminals 4 and 4a are microwave oscillation output terminals. This negative resistance circuit is constructed in the form of an emitter E-coupled collector C output having a base B grounded. The frequency variable microwave oscillator is characterized by being small and inexpensive.

[0003]

However, in the variable capacitance element 1 ', a voltage is applied to the semiconductor diode in the opposite direction to form a depletion layer without carriers, and its thickness is controlled by the magnitude of the voltage. Since the material is a semiconductor, there are drawbacks such as a large loss in a high frequency band due to a conductor loss and a large temperature change. Further, there is a problem that the circuit configuration becomes complicated in order to ensure the insulation between the control system and the signal system. Therefore, the present invention solves the above-mentioned drawbacks and problems of the prior art,
It is an object of the present invention to provide a temperature variable frequency microwave oscillator with low noise and wide variation range.

[0004]

The variable frequency microwave oscillator according to the present invention is a combination of a variable capacitance element and an inductance element which change the capacitance by changing the distance between two metal flat plates. A mechanical method that can be electrically controlled is used as a means for changing the distance between the two metal flat plates.

[0005]

According to the above structure, the variable capacitance element is basically based on the structure of a parallel plate capacitor using air or the like having a small loss as an insulating medium, and the distance between the parallel plates can be electrically controlled mechanically. Since it can be changed subtly by the displacement element, by combining it with a low-loss inductance element, it is possible to realize a temperature stable frequency variable microwave oscillator with low noise and a wide frequency variation range.

[0006]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a diagram for explaining the basic configuration of the present invention. The left part of the figure shows an example of parallel connection of the variable capacitance element 5 having parallel plates 5 and 5a and the inductance element 2. Reference numeral 3 is a negative resistance circuit composed of transistors. Terminals 4 and 4a are microwave oscillation output terminals. This negative resistance circuit is constructed in the form of an emitter E-coupled collector C output having a base B grounded. The variable capacitance element 1 is configured to change the distance d between the two metal parallel plates 5 and 5a by Δd by a mechanical means. When the surface area of the metal flat plates 5 and 5a is S and the relative permittivity of the insulating medium is ε, the capacitance C of the variable capacitance element 1 is

## EQU1 ## C = K ₁ εε _o S / d Here, ε _o is the dielectric constant of vacuum, and K ₁ is a proportional coefficient smaller than 1. One of the two metal flat plates 5,
When the distance d of 5a is reduced by Δd, the electrostatic capacitance at this time is

## EQU2 ## It changes as C = K ₁ εε _o S / (d−Δd). At this time, assuming that the inductance of the inductance element 2 is L, the resonance frequency f of the parallel resonance circuit of FIG.

F = 1 / (2π√LC) = √d−Δd / (2π√K ₁ εε _o SL) Along with this, only the microwave of the frequency component expressed by the equation 3 is amplified by the negative resistance circuit 3, and the microwave of the same frequency is output to the terminals 4 and 4a. FIG. 2 shows one embodiment of the present invention. As the inductance element 2, a strip line 2a with a short-circuited termination is used. In addition, as the variable capacitance element 1, a configuration in which the distance between the two metal parallel plates 5 and 5a is changed by the mechanical displacement element 6 is used. In the figure, 7 is a ground conductor, 8 is an insulator, and 9 is a structure for fixing the mechanical displacement means 6. A part of the ground conductor 7 rises, and one of the parallel plates 5a is fixed thereon. The strip line 2a and the metal flat plate 5 are connected. Also, they are connected to the emitter E of the transistor Tr. The base is a coupling capacitor C
It is connected to the ground conductor 7 via 2. The collector C becomes the output terminal 4 via the coupling capacitor C1. One of the output terminals 4a is connected to the ground conductor 7. As a result, the variable frequency microwave oscillator using the parallel resonator of the variable capacitance element 1 having the capacitance C with respect to the ground conductor and the inductance element 2 was realized. In this embodiment, the distance d between the two parallel plates is about 20 μm. FIG. 3 shows another embodiment of the present invention for series resonance. The difference from FIG. 2 is that the two metal parallel plates 5 and 5a are strip lines 2
It is a point connected in series with a. As a result, a series resonator in which the variable capacitance element 1 having the capacitance C is connected to the inductance element 2 in series is realized, and a variable frequency microwave oscillator in which this and a negative resistance circuit are combined can be realized. . In this embodiment, the distance d between the two parallel plates is about 20 μm. FIG. 4 shows the structure of the piezoelectric element 6a as the mechanical displacement element 6 used for carrying out the above-described FIG. 2 and FIG. This element is terminal 1
The displacement is obtained by applying a voltage V to 0 and 10a. By applying a voltage of 150 V to the terminals 10 and 10a, Δd = 10 μm was obtained. In general, the displacement amount Δd of the piezoelectric element 6a is proportional to the terminal voltage V, as in Δd = K ₂ V, and therefore the equation 2 is as follows.

## EQU4 ## C = K ₁ ε ε _o S / (d−K ₂ V) Thus, the capacitance C can be changed by changing the terminal voltage V, and the oscillation frequency changes according to Expression 3. A variable frequency microwave oscillator has been realized. FIG. 5 shows the structure of a magnetostrictive element 6b as a mechanical displacement means 6 used to execute the above-described FIG. 2 and FIG. In this element, a magnetic field is generated by the coil 12 when a current I is applied to the terminals 11 and 11a, whereby the displacement of the magnetostrictive element is obtained. 2A for terminals 11 and 11a
Δd = 10 μm was obtained by applying the current of. In general, the displacement amount Δd of the magnetostrictive element 6b is proportional to the square of the terminal current I, as in Δd = K ₃ I ^2. Therefore, the equation 2 is as follows.

[Equation 5] C = K ₁ εε _o S / (d−K ₃ I ² ) Thus, the capacitance C can be changed by changing the terminal current I, and the oscillation frequency can be changed according to Equation 3. A variable frequency microwave oscillator 5 that changes can be realized. FIG. 6 shows the piezoelectric element 6 of FIG. 4 in the embodiment of FIG.
It is a figure which shows the characteristic of the frequency variable microwave oscillator of this invention when a is used. The oscillation frequency could be changed from 1.6 GHz to 1.13 GHz by changing the terminal voltage from 0 to 150V. FIG. 7 shows FIG.
6 is a diagram showing the characteristics of the variable frequency microwave oscillator of the present invention when the magnetostrictive element 6b of FIG. 5 is used in the example of FIG. The oscillation frequency could be changed from 1.6 GHz to 1.2 GHz by changing the terminal current from 0 to 2A. FIG. 8 shows an application example of the variable frequency microwave oscillator of the present invention. A part of the microwave output from the oscillator is guided to the divider by the directional coupler. Here, the frequency is divided and enters the divider. The frequency divider outputs a signal controlled by the computer which sets the frequency. This output and the signal of the crystal oscillator are compared by the phase comparator, and the control signal corresponding to the difference between these signals is introduced to the terminal of the mechanically controllable mechanical displacement element. By such an operation, the microwave output whose frequency is stabilized is supplied to the outside through the amplifier. The variable frequency microwave oscillator of the present invention is an oscillator that is extremely suitable for the above applications.

[0007]

According to the present invention, as compared with the prior art, a parallel plate capacitor using a low-loss insulator as a medium is used as a variable capacitance element, and the distance between the parallel plates is set to a mechanical displacement element. It is possible to provide a low-noise, wide-variable, temperature-stable, and frequency-variable microwave oscillator by combining this with a low-loss inductance element.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a basic principle of the present invention.

FIG. 2 is a sectional view showing the structure of the embodiment of the present invention.

FIG. 3 is a sectional view showing the structure of the embodiment of the present invention.

FIG. 4 is a structural cross-sectional view of a component for realizing an embodiment of the present invention.

FIG. 5 is a structural cross-sectional view of a component for realizing an embodiment of the present invention.

FIG. 6 is a characteristic diagram of an example of the present invention.

FIG. 7 is a characteristic diagram of an example of the present invention.

FIG. 8 is a block diagram showing an application example of the present invention.

FIG. 9 is a component symbol diagram showing a conventional technique.

[Explanation of symbols]

 1 Variable Capacitance Element 2 Inductance Element 3 Negative Resistance Circuit 4 Output Terminal 5 Metal Parallel Plate 6 Mechanical Displacement Element 7 Ground Conductor 8 Insulator 9 Structure 10 Control Terminal 11 Control Terminal 12 Coil

Claims (4)

[Claims] 1. A microwave resonator including a combination of an electrostatic capacitance element and an inductance element, and a microwave oscillator in which the microwave resonator and a negative resistance circuit are coupled to each other. The microwave resonator whose resonance frequency changes by changing the capacitance,
In the frequency variable microwave oscillator, in which the oscillation frequency of the microwave oscillator changes in accordance with the change of the resonance frequency of the microwave resonator, the capacitance element is
A variable frequency microwave oscillator using a variable capacitance element capable of changing a distance between metal flat plates by a mechanical means capable of being electrically controlled. 2. The variable frequency microwave oscillator according to claim 1, wherein a piezoelectric element is used as an electrically controllable mechanical means for changing a distance between the two metal flat plates. 3. The frequency variable microwave oscillator according to claim 1, wherein a magnetostrictive element is used as an electrically controllable mechanical means for changing a distance between the two metal flat plates. 4. The frequency variable microwave oscillator according to claim 1, wherein the inductance element is formed of a microstrip line.