JP3645951B2 - Microwave dielectric oscillator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a parallel feedback type microwave dielectric oscillator using a dielectric resonator, which is used in, for example, a Doppler module and other sensors using microwaves.
[0002]
[Prior art]
FIG. 4 shows an example of a configuration of a conventionally used parallel feedback type microwave dielectric oscillator. The microstrip input matching circuit 2 is connected to the gate of the FET 1, the microstrip output matching circuit 3 is connected to the drain, and the choke coils 4 and 5 for preventing the microwave signal from passing are connected to these 2 and 3, respectively. Is configured.
The gate bias and the drain bias of the FET 1 are supplied from a bias circuit (not shown) to the gate bias supply terminal 6 and the drain bias supply terminal 7, respectively. On the other hand, the dielectric resonator 12 is coupled to the microstrip line 10 and the microstrip line 11 at coupling points 13 and 14 at the resonance frequency fo, thereby forming a resonance circuit 16. The amplifier circuit 15 and the resonance circuit 16 are connected in parallel via terminals 8 and 9 to constitute a parallel feedback dielectric oscillator.
[0003]
At the resonance frequency fo of the dielectric resonator 12, the loop gain which is the sum of the gain of the amplifier circuit and the signal passing loss in the signal path 9 → 11 → 14 → 12 → 13 → 10 → 8 of the resonance circuit is 0 db or more, and When the loop phase determined by the sum of the phase change amount of the amplifier circuit and the phase change amount in the signal path 9 → 11 → 14 → 12 → 13 → 10 → 8 of the resonance circuit becomes 360 °, the dielectric oscillator of FIG. Is transmitted at fo, and the oscillation output signal is taken out from the output terminal 18 via the DC cut capacitor 17.
[0004]
[Problems to be solved by the invention]
In the microwave dielectric oscillator as described above, theoretically, if the loop phase is N × 360 ° (N = 1, 2, 3,...), Positive feedback is applied, and at a predetermined oscillation frequency fo. Oscillation will occur, but every time N increases by 1, the transmission line length must be increased by λ. The longer the transmission line length is, the more the line loss increases and the amplifier gain becomes insufficient for oscillation. . Therefore, the loop phase is kept at 360 ° so that the transmission line length is shortened. However, when the phase change of the amplifier circuit becomes large, the amount of phase change of the resonance circuit needs to be reduced by that much, and it becomes necessary to bring the amplifier circuit and the dielectric resonator close to each other. There has been a problem that the amplifier circuit and the dielectric resonator are electromagnetically coupled to each other and cannot operate normally.
[0005]
Further, the amplifier circuit is designed so that the gain is maximized at the resonance frequency fo of the resonance circuit, and the gain is lost at a frequency exceeding fo, but the gain cannot be suppressed as the frequency becomes lower in the band below fo. When resonance points exist at the following frequencies, there is a risk of causing unnecessary oscillation that is unrelated to the resonance frequency of the dielectric resonator.
Therefore, due to the above problems, design restrictions have increased and design man-hours have increased.
[0006]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a microwave dielectric oscillator that eliminates such drawbacks and has a stable operation with a simple configuration.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a dielectric oscillator according to the present invention includes a transistor, an amplifier circuit including an input / output matching circuit of the transistor, a dielectric resonator, and the dielectric resonator connected in parallel to the amplifier circuit. A parallel feedback dielectric oscillator comprising: a resonant circuit including two transmission lines that are electromagnetically coupled to the dielectric resonator and connected to an input terminal and an output terminal of the amplifier circuit, respectively. Pass the oscillation frequency of the dielectric oscillator between the input terminal and the transmission line connected to the input terminal or between the output terminal of the amplifier circuit and the transmission line connected to the output terminal. At least one high-pass filter, which is configured to suppress a loop gain in a frequency band lower than the oscillation frequency of the dielectric resonator .
[0008]
In addition, an amplifier circuit having a transistor and an input / output matching circuit for the transistor, a dielectric resonator, and an electromagnetic coupling with the dielectric resonator to connect the dielectric resonator in parallel to the amplifier circuit are coupled to the amplifier. A parallel feedback dielectric oscillator comprising: a resonant circuit comprising two transmission lines connected to an input terminal and an output terminal of the circuit; and the transmission line connected to the input terminal of the amplifier circuit and the input terminal A plurality of high-pass filters having a pass band of an oscillation frequency of the dielectric oscillator between the output terminal of the amplifier circuit and the transmission line connected to the output terminal, and the dielectric The loop gain in the frequency band lower than the oscillation frequency of the oscillator is configured to be low .
[0009]
With this configuration, the high-pass filter has the effect of advancing the phase, and accordingly, the distance between the amplifier circuit and the dielectric resonator can be increased, and electromagnetic coupling between the resonator and the amplifier circuit is prevented. be able to.
Furthermore, the high-pass filter can suppress the loop gain in a frequency band lower than fo.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram showing an embodiment in which the present invention is used in a microwave dielectric oscillator. 4, the same reference numerals as those in FIG. 4 denote the same or corresponding parts, 19 denotes a capacitor, 20 denotes an inductor 21 denotes a high-pass filter.
[0011]
One end of the resonance circuit 16 is connected to the output side of the amplifier circuit via the microstrip line 11 at the terminal 9, and the other end is connected via the microstrip line 10 to the capacitor 19 and the inductor 20 via the high pass filter 21. 8 is connected to the input side of the amplifier circuit. 17 is D.M. A C-cut capacitor 18 is a terminal for extracting an oscillation signal output.
[0012]
In such a parallel feedback type dielectric oscillator composed of the amplifier circuit 15, the resonance circuit 16, and the high-pass filter 21, the loop gain is 0 db or more and the loop phase is 360 ° at the resonance frequency fo of the dielectric resonator 12. When it becomes, it oscillates.
[0013]
In this case, the distance between the dielectric resonator 12 and the amplifier circuit 15 is determined according to the condition that the loop phase is 360 °, but the microstrip lines 10 and 11 are made longer by the effect of the phase advance of the high-pass filter 21. Therefore, the distance between the amplifier circuit 15 and the dielectric resonator 12 can be set such that electromagnetic coupling does not occur, that is, a stable operation is not a problem. In this case, the high-pass filter is designed to have a steep shoulder characteristic by determining the constants of the capacitor 19 and the inductor 20 so that the pass loss is reduced with the frequency fo as a pass band and the cut-off frequency is close to a frequency close to fo. As a result, the loop gain in the low frequency band can be greatly suppressed without sacrificing the loop gain at the frequency fo, so that unnecessary oscillation at a low frequency below fo can be prevented.
[0014]
FIG. 2 is a diagram showing an embodiment in which the high-pass filter 21 is multistaged. In this figure, the same reference numerals as those in FIG. 1 denote the same or corresponding parts.
As shown in the figure, the high-pass filter 21 is connected in multiple stages between the microstrip line 10 of the resonance circuit 16 and the input terminal of the amplifier circuit 15. Since the phase advance amount can be increased by this multi-stage connection, it is possible to adjust so that the distance between the dielectric resonator 12 and the amplifier circuit 15 can be further increased, and it is unnecessary because the loop gain in the low frequency region is further suppressed. The risk of oscillation is further reduced.
[0015]
As mentioned above, although embodiment of this invention was described, this invention is not restricted to this, A various change is possible. For example, when the use frequency band is relatively low, as shown in FIG. 3, it is possible to use a microwave BJT (bipolar transistor) 22 such as an HBT instead of the FET 1 of FIG. In the above embodiment, the high-pass filter is inserted between the input terminal of the amplifier circuit and the transmission line connected thereto, but is inserted between the output terminal of the amplifier circuit and the transmission line connected thereto. Also good.
[0016]
【The invention's effect】
As described above, according to the first aspect of the present invention, in the parallel feedback type microwave dielectric oscillator, the high-pass filter is inserted between the amplifier circuit and the resonance circuit. In order to satisfy a loop phase that is a condition for oscillation at a frequency, the dielectric resonator and the amplifier circuit can be stably operated without being too close, and unnecessary oscillation in a low frequency band can be prevented.
According to the invention of claim 2, the phase advance amount can be increased by connecting a plurality of high pass filters having the oscillation frequency as a pass band between the resonance circuit and the amplifier circuit, and the number of high pass filters can be selected appropriately. By doing so, the degree of freedom of design can be increased and the number of design steps can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of the present invention.
FIG. 2 is a diagram showing another embodiment of the present invention.
FIG. 3 is a diagram showing still another embodiment of the present invention.
FIG. 4 is a diagram showing an example of a conventional parallel feedback microwave dielectric oscillator.
[Explanation of symbols]
1 FET
2 Microstrip input matching circuit 3 Microstrip output matching circuit 4, 5 Bias supply choke coil 10, 11 Microstrip line 12 Dielectric resonator 15 Amplifying circuit 16 Resonant circuit 17 DC cut capacitor 18, oscillation signal output terminal 19, capacitor 20, inductor 21, high pass filter 22 BJT (bipolar transistor)

Claims (2)

An amplifier circuit comprising a transistor and an input / output matching circuit for the transistor; a dielectric resonator; and an electromagnetic coupling with the dielectric resonator for parallel connection of the dielectric resonator to the amplifier circuit, In a parallel feedback dielectric oscillator comprising: a resonance circuit comprising two transmission lines connected to an input terminal and an output terminal; and an input terminal of the amplifier circuit and the transmission line connected to the input terminal. during, or the provided output terminal of the amplifier circuit, at least one high-pass filter and the pass band of the oscillation frequency of the dielectric oscillator between the transmission line connecting the output terminal, wherein the dielectric resonator A microwave dielectric oscillator characterized by suppressing a loop gain in a frequency band lower than the oscillation frequency of the ceramic. An amplifier circuit comprising a transistor and an input / output matching circuit for the transistor; a dielectric resonator; and an electromagnetic coupling with the dielectric resonator for parallel connection of the dielectric resonator to the amplifier circuit, In a parallel feedback dielectric oscillator comprising: a resonance circuit comprising two transmission lines connected to an input terminal and an output terminal; and an input terminal of the amplifier circuit and the transmission line connected to the input terminal. during, or connects the output terminal of the amplifying circuit, a plurality of high-pass filter and the pass band of the oscillation frequency of the dielectric oscillator between the transmission line connecting the output terminals of the dielectric oscillator A microwave dielectric oscillator characterized by suppressing a loop gain in a frequency band lower than an oscillation frequency .

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