JPH0366213A - Microwave oscillator - Google Patents

Abstract

PURPOSE:To suppress spurious oscillation by connecting a FET to ground through a parallel circuit comprising a series resonance element and a sustenance element. CONSTITUTION:A parallel circuit 16 is connected to a drain terminal 6. A drain terminal 6 of a FET 3 is connected to ground similarly as a conventional constitution at a frequency fOSC by selecting an electric length of a 2nd microstrip line 9 to be nearly 90 deg. to obtain a required oscillation wave. On the other hand, the susceptance B' of a 3rd microstrip line 15 is set to be B+B'=0 at a resonance frequency fX in the undesired mode of a dielectric resonator 2, where B is the susceptance of the 2nd microstrip line 9. Thus, a voltage across the parallel circuit 16 is increased and acts like a negative feedback voltage with respect to an input voltage to a gate terminal 4 to cancel the reflection gain of the FET 3.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a microwave oscillator that suppresses spurious oscillations at frequencies other than desired frequencies.

[Prior art] Here, an FE with a grounded drain is used as a three-terminal semiconductor device.
Explanation will be given by taking as an example a microwave oscillator using T and a dielectric resonator as a resonant circuit. FIG. 5 shows, for example, the Journal of the Institute of Electronics and Communication Engineers Vol. J69-B No. 11 (
This is an example of the configuration of a microwave oscillator having a conventional configuration as described in pages 1415 to 1421 of the following publication (November 1986), in which figure (a) is a perspective view and figure (b) is an equivalent circuit. In FIG. 5, (■) is a dielectric substrate, (2
) is a dielectric resonator, (3) is a FET, (4) is a FET (
3) is the gate terminal, (5) is the source terminal of FET (3), (6) is the drain terminal of FET (3), (7> is the first micro terminal loaded with dielectric resonator (2) 1-slip line, (8> is a terminating resistor, (9> is a second microstrip line with an open end, (10) is an output matching circuit, (11) is an output terminal, (12) is a choke inductor , (13) are power supply terminals, and (1, 4) are bias circuits.

Next, the operation will be explained. In general, an FET with a grounded drain has a large amount of internal feedback and operates as an in-phase amplifier circuit, so it is often used as a semiconductor element for oscillation. In the microwave oscillator with the conventional configuration shown in Fig. 5,
The required oscillation frequency (hereinafter f″O
By connecting the second microstrip line (9) with an electrical length of approximately 90 degrees at the angle of 90°, the FET (3)
The drain terminal (6〉) of SC is grounded.At this time, a positive power supply voltage is applied to the power supply terminal (t3), and a DC current is applied to the choke inductor (12), FET (3), and output matching circuit (
10>, and then the bias circuit (14), and then the FE
T(3) is operating. Furthermore, gate terminal (4)
A suitable output matching circuit (10) is connected to the SC source terminal (5) so that the FET (3) seen from the source has a reflection gain at the frequency f. Then, the dielectric resonator (2), which resonates at the frequency f and causes a large reflection SC, is connected to the terminal (/ By connecting to the SC output terminal (11), this microwave oscillator oscillates at a frequency f.At this time, the oscillation wave is output to the SC output terminal (11).

[Problems to be Solved by the Invention] In a microwave oscillator with such a conventional configuration, the drain terminal (6>) is connected to the second microstrip line (
9), it is grounded with low impedance near the frequency f.

SC Therefore, near the frequency f, I? as seen from the gate terminal (4) SC? ET(3) has anti-body gain. on the other hand,
The dielectric resonator (2) is designed so that SC resonance of TEol, mode occurs at f, but at the same time resonance due to other unnecessary modes also occurs near the frequency f. In the wave oscillator, as shown in FIG. 6, in addition to the frequencies r., . . . , the oscillation condition is easily satisfied at the resonance frequency f SC due to an unnecessary mode in the vicinity of f, and there is a problem in that spurious oscillation is likely to occur.

This invention was made to solve the above-mentioned problems, and aims to provide a microwave oscillator that does not generate spurious oscillations.

[Means for Solving the Problems] A microwave oscillator according to the present invention has an FET (3) grounded by a parallel circuit consisting of a series resonant element and a susceptance element.

Function] In the microwave oscillator according to the present invention, FET (3>
is grounded by a parallel circuit consisting of a series resonant element and a susceptance element. The constant SC of this series resonant element is set so that it resonates in series at a frequency f 2 , and the constant of the susceptance element is set so that the entire parallel circuit resonates in parallel at a frequency f 2 . Therefore,
FET (3) operates similarly to the conventional configuration since at frequency f the SC parallel circuit has a low impedance, and at frequency r the parallel circuit has a high impedance. Therefore, at frequency f, the voltage across the parallel circuit acts as a negative feedback voltage with respect to the input voltage to terminal (4) to terminal (4), so the reflection gain of FET (3) seen from terminal (4) Due to the effect of this parallel circuit, even if there is resonance due to an unnecessary mode of the dielectric resonator (2) at the frequency f, the gate terminal (4)
Since the reflection gain of the FET (3) seen from above is reduced, no spurious oscillation occurs.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. Here, as a parallel circuit, a parallel circuit of two microstrip lines each having an open end and different electrical lengths will be described as an example. FIG. 1 shows a microwave oscillator according to the present invention; FIG. 1(a) is a perspective view, and FIG. 1(b) is an equivalent circuit. In Figure 1, (15) is the third microstrip line with an open end, and (16> is the second and third microstrip line (9) connected in parallel).
This is a parallel circuit consisting of (15). Next, the operation will be explained. In the microwave oscillator according to the configuration of the present invention shown in FIG. 1, a parallel circuit (16) is connected to the drain terminal (6). Frequency f. ,.

Now, by setting the electrical length of the second microstrip line (9) to approximately 90 degrees, the drain terminal (6) of the FET (3) can be grounded as in the conventional configuration, and the desired oscillation wave can be obtained. On the other hand, at the resonant frequency f due to the unnecessary mode of the dielectric resonator <2>, the susceptance B of the second microstrip line (9>) is capacitive (f > f).
Some x osc or it becomes inductive (f<f). Frequency fxX
In O3C, the septance B° of the third microstrip line (1, 5) is set so as to satisfy the following equation with respect to the susceptance B of the second microstrip line (9).

B+B'2O(1) At a frequency that satisfies this first equation, the parallel circuit (16) resonates in parallel and becomes high impedance. Therefore, at frequency f, the voltage across the parallel circuit (↑6) increases, and this voltage acts as a negative feedback voltage with respect to the input voltage to terminal (4) to terminal (4), so that The reflection gain of F"ET (3) is canceled out. Therefore, the microwave oscillator configured according to the present invention satisfies the oscillation condition at frequency f as shown by the solid line in FIG. Since the gain is reduced, the oscillation × condition is not satisfied, so spurious oscillation does not occur.

In the above embodiment, the parallel circuit (16) is a parallel circuit of two microstrip lines of different lengths, but a parallel circuit of three or more microstrip lines of different lengths may be used. FIG. 3 shows an example in which three microstrip lines of different lengths are used as a parallel circuit. In FIG. 3, (7) is the fourth microstrip line with an open end. In this case, f
os.

This is effective when there are two resonance frequencies due to unnecessary modes of the nearby dielectric resonator (2) (the respective resonance frequencies are abbreviated as fxl and fx2). In this case, the second microstrip line is set to approximately 90 degrees SC at the frequency f, and the susceptance B- of the third microstrip line and the fourth microstrip line (17
) at frequencies f1 and fx2, the third and fourth microstrip lines (15
) (19>).In this case, at frequencies fxl and fx2, the FE seen from the gate terminal (4)
Since the reflection gain of T(3) is reduced, no spurious oscillations occur at these frequencies.

Further, in the above embodiment, a microstrip line is used as the parallel circuit (16), but a coplanar line or a slot line may be used depending on the form of the line used for the microphone D-wave oscillator. Also, as a parallel circuit (↑6),
A lumped constant circuit may also be used. Figure 4 shows a parallel circuit (16
) is an example in which all lumped constant circuits are used. In Figure 4, (18) is a series resonant circuit consisting of capacitor C1 and inductor L, and (19) is capacitor C2. In this case as well, the resonant frequency due to the unnecessary mode of the dielectric SC body resonator (2) near f is
Then, the values of C1 and C2L should be set so as to satisfy the following equation.

2πr −(C1·L)′. 5 (3) 5C ((2πfC□ )-1 +2πf C2 In this case as well, the frequency fx 2πfL)-1 O(4) Since the reflection gain of FET (3) related to the Gerd terminal (4) is reduced, these Spurious oscillation at the frequency does not occur, and the same effect is achieved.

In addition, in the above embodiment, an FET (
Although explained in 3), other transistors such as bipolar transistors may also be used, and similar effects can be achieved.

In addition, in the above embodiment, a dielectric resonator (2
Although described above, a resonant circuit using a YIG resonator, a SAW resonator, or a variable capacitance diode may be used, and the same effect can be achieved.

[Effect of the invention 1 As described above, according to the present invention, the FET is grounded in a parallel circuit that has low impedance at the required oscillation frequency and high impedance at the resonant frequency caused by the unnecessary mode of the dielectric resonator. By doing this, spurious oscillation can be suppressed.

[Brief explanation of drawings]

0 FIG. 1 is a perspective view and an equivalent circuit of a microwave oscillator according to an embodiment of the present invention, FIG. 3 and 4 are equivalent circuits of parallel circuits according to other embodiments of the present invention, FIG. 5 is a perspective view and equivalent circuit of a microwave oscillator with a conventional configuration, and FIG. 6 is a microwave oscillator with a conventional configuration. FET seen from the oscillator gate terminal
FIG. 3 is a gain and oscillation spectrum diagram of FIG. In the figure, (1) is a dielectric blocking plate, (2) is a transparent resonator, and (3
〉 is FET, (7〉, (9〉, (15), and (17
〉 is a micro strip line, (8) is a terminating resistor, (
10) is the output matching circuit, (1) is the output terminal, (■2)
is the choke inductor, (13> is the power supply terminal, (14)
is a bias circuit, and (16> is a parallel circuit. In the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] A three-terminal semiconductor element having an input terminal, an output terminal, and a common terminal, a resonant circuit connected to the input terminal of the three-terminal semiconductor element, and a matching circuit connected to the output terminal of the three-terminal semiconductor element. A microwave oscillator, characterized in that a parallel circuit consisting of a series resonant circuit and an element having a predetermined susceptance is connected between a common terminal of the three-terminal semiconductor element and a ground conductor.