JPS592407A - Microwave oscillator - Google Patents

Abstract

PURPOSE:To improve the degree of freedom of QL value selection of a main resonator, to increase easily the value and to make the value of QL stable by providing a coupling line between a connecting point of the main resonator and a transistor (TR). CONSTITUTION:One end of a coupling line 21 is connected to the connecting point 23 on the main resonator 1 made of the transmission line of about lambda/4 in an objective frequency, one end of which is grounded, and the other end of the line 21 is connected to the base of the TR2 for forming an oscillating circuit. The coupling line 21 is arranged between the connecting point 23 of the main resonator 1 and the base of the TR2 and the length l2 is selected so that the reflecting factor viewed from the TR2 to the main resonator 1 is an optimum phase. Further, the QL of the main resonator 1 is set optionally with the ratio of the characteristic impedance of the main resonator 1 and the line 21 and the position of the connecting point 23, that is, the ratio of the length l1 from the grounding point to the connecting point 23 to the length l0 of the main resonator 1. The degree of freedom of the decision of the QL is increased in this way, the QL is improved easily and the QL is kept stable.

Description

[Detailed Description of the Invention] (Technical Field of the Invention) The present invention relates to a microwave oscillator configured by a planar circuit, which has a large degree of freedom in determining the load Q and can easily increase the load Q. be.

(Prior art and problems) When constructing a microwave oscillator using a planar circuit, the main resonator is a λ/4 oscillator made of a microstrip line.
(λ is the wavelength on the line) A resonator is generally used. In a microwave oscillator configured as a planar circuit in this way, as long as the main resonator is configured with a microstrip line, the Q (Qo) of the resonator itself is not high, so when an active element circuit such as an oscillation transistor is coupled The load Q (QL) tends to be low, and therefore the oscillation frequency stability is poor. Therefore, it is desirable to configure the circuit so that QL is as high as possible. Furthermore, when using a microwave oscillator as a frequency modulator, the lower Chr is, the more advantageous it is to widen the modulation frequency bandwidth. However, even in the case of a frequency modulator, QL must be maintained at a required value or higher in order to keep FM noise low.

As described above, in a microwave oscillator configured by a planar circuit, it is very important that QL can be easily designed to a desired value and that QL has good reproducibility in manufacturing. However, conventional microwave generators generally have a main resonator and an active element circuit coupled directly, or a main resonator and an active element circuit coupled via a capacitor. It has been difficult to arbitrarily determine the value of and maintain it.

FIG. 1 shows an example of a conventional microwave oscillator, in which a transistor circuit is directly connected to one end of a main resonator. In the figure, 1 is a λ/4 main resonator whose one end is grounded, and the base of a transistor 2 is directly connected to the other end to form an oscillator. The collector of the transistor 2il-i is grounded, and the output is taken out to the output terminal 4 via the matching circuit 6. The transistor 2 is supplied with an emitter bias voltage from a terminal 6 via a choke 5, and is supplied with a base bias voltage from a terminal 8 via a choke 7. 9 and 10 are decoupling capacitors, respectively. Note that 11 is a coupling line arranged close to and parallel to the main resonator 1, and together with a capacitor 12 constitutes a sub-resonator. The device operates as a frequency modulator by changing the oscillation frequency by applying a bias voltage.

15 is a decoupling capacitor.

In the microwave oscillator shown in Figure 1, the transistor is directly connected to the main resonator and the load Q is low, so the S/u is poor.
Transistor parameters have a large effect on the oscillation frequency, making it difficult to improve temperature stability. Furthermore, even when a frequency modulator is formed by providing a coupling line, the degree of coupling via the gap between the coupling line and the main resonator is likely to be influenced by the etching accuracy of the gap.

FIG. 2 shows another example of a conventional microwave oscillator, in which a main resonator and a transistor circuit are connected via a capacitor. In this figure, the same parts as in FIG. 1 are indicated by the same numbers, and 16 is a coupling capacitor which connects the main resonator 1 to the base of the transistor 2, thereby forming an oscillator. In other respects, it is similar to the circuit shown in FIG.

In the microwave oscillator shown in FIG. 2, the degree of coupling between the main resonator and the transistor circuit can be changed by selecting the capacitance value of the capacitor, and therefore the QL can be changed to some extent. However, this requires a capacitor with high precision, and the temperature characteristics of the capacitor do not affect the oscillation frequency, so there are many difficulties in actual manufacture.

□In this way, in a conventional microwave oscillator, for example, in the circuit format shown in Figure 1, the transmission line serving as the main resonator is directly connected to the oscillation active element circuit, and QL is the characteristic impedance of the main resonator 1. It is determined by However, it is difficult to maintain the value accurately and stably.Furthermore, in both image formats, the coupling degree of the sub-resonator is adjusted by the gap between the transmission lines, so variations due to etching accuracy are large. Hey.

(Objective of the Invention) The present invention attempts to solve the problems of the prior art, and its purpose is to select a QL value in the main resonator in a microwave oscillator using a planar circuit structure. It is an object of the present invention to provide a circuit type that has a large degree of freedom, is easy to increase its size, and can maintain a stable QL value.

(Embodiment of the Invention) FIG. 6 shows the configuration of an embodiment of the microwave oscillator of the present invention. In the figure, the same parts as in Figures 1 and 2 are indicated by the same numbers, 21 is a coupling line, 22 is a DC blocking capacitor, 26 is a coupling point, 2
4 is an inductance, and 25 is a coupling point.

In FIG. 2, one end of the coupling line 21 is connected to a connection point 23 on the main resonator 1, which is made up of a transmission line of approximately λ/4 at the target frequency and whose one end is grounded.
The other end is connected to the base of the transistor 2 via a DC blocking capacitor 22 to form an oscillation circuit. The coupling line 21 is arranged between the connection point 26 of the main resonator 1 and the base of the transistor 2, and its length t2 is set so that the reflection coefficient when looking at the main resonator 1 from the transistor has an optimal phase. selected. Further, the ratio of the respective characteristic impedances of the main resonator 1 and the coupling transmission line 21,
By the ratio of the length tl from the ground to the connection point 26 and the length 1 of the main resonator 1,
The QL of the main resonator 1 can be set arbitrarily. A capacitor 22 is provided on the side of the main resonator 1 to block the base bias voltage.

In this way, in the microwave oscillation circuit shown in FIG.
There is a large degree of freedom in determining the value of QL, and it is easy to increase QL. Since the value of QL is determined by the shape and positional relationship of the main resonator 1 and the coupling transmission line 21,
The value of QL is stable and the oscillation frequency changes little.

In the circuit shown in FIG. 6, an auxiliary resonator is formed by the inductance 24 and the capacitor 12, and a varactor diode 16 is connected to this to change the varactor diode voltage applied from the terminal 14 to operate as a frequency modulator. be able to. At this time, inductance 2
4, that is, the length t3 from the ground to the connection point 25, and the length 1.4 of the main resonator 1. By changing the ratio between the sub-resonator and the main resonator, the amount of coupling between the sub-resonator and the main resonator can be changed, thereby allowing the modulation sensitivity and linearity to be freely determined. Therefore, the degree of coupling is not affected by etching accuracy as in the conventional circuits shown in FIGS. 1 and 2.

FIG. 4 shows the structure of another embodiment of the microwave oscillator of the present invention. In this figure, the same parts as in FIG. 3 are designated by the same numbers, 26 is a field effect transistor (FET), 27 is a gate bias terminal, and 28 is a source bias terminal.

In the embodiment shown in FIG. 4, an FET 26 is used in place of the transistor 2 in the embodiment shown in FIG.
The gate G of the FET 26 is connected to one end of the coupling line 21 via the DC blocking capacitor 22, the drain D is grounded, and the source S is connected to the matching circuit 6. Furthermore, a gate bias is supplied from a gate bias terminal 27 via a choke 7, and a source bias is supplied from a source bias terminal 28 via a choke 5. As a result of this configuration, the microwave oscillator shown in FIG. 4 operates in the same manner as the microwave oscillator shown in the embodiment shown in FIG. 6, and has a large degree of freedom in determining QL. In addition, it is easy to increase the QL, and the QLO value is stable and the oscillation frequency stability is high.

(Effects of the Invention) As explained above, according to the microwave oscillator of the present invention, the QI
, the degree of freedom in decision making is large, and it is easy to increase the QL, and it is also possible to keep the QL stable. Therefore, the oscillation frequency stability can be increased, and manufacturing reproducibility can be improved, which is extremely effective.

[Brief explanation of drawings]

1 and 2 are diagrams showing an example of the configuration of a conventional microwave oscillator, and FIGS. 6 and 4 are diagrams each showing the configuration of an embodiment of the microwave oscillator of the present invention. 1...λ/4 main resonator, 2...transistor, 6...
...matching circuit, 4...output terminal, 5...choke,
6... Emitter bias terminal, 7... Choke, 8
・・・He-7, 7: Earth terminal, 9.10... Decoupling capacitor, 11... Coupling line, 12.
・・Capacitor, 1 ・・Nokurakta diode, 1
4... (actor diode terminal, 15.
...decoupling capacitor, 16...coupling capacitor, 21...coupling line, 22...DC blocking capacitor, 23...coupling point, 24...inductance, 25...coupling point , 26... Field effect transistor (FET), 27... Gate terminal (earth terminal,
28... Source bias terminal patent applicant Fujitsu Ltd. Representative Patent Attorney Kugo Tamamushi (3 others) No. 10 Ri M 2 Figure 3 Figure 4I21

Claims (1)

[Claims] In a microwave oscillator in which a main resonator consisting of a λ/4 transmission line with one end grounded is connected to an active element circuit such as a transistor to form an oscillation circuit, a connection point selected on the main resonator and the A microwave oscillator characterized in that a transmission line for coupling is provided between an active element circuit and an active element circuit.