JPS643403B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a microwave oscillator used as a local oscillator for microwave communication equipment, SHF receivers, and the like.

Prior Art FIG. 8 shows an example of the configuration of a conventional microwave oscillator using a field effect transistor (FET).
1 is an FET, and a strip line 3 with an open end and a length of about 1/4 wavelength of the oscillation frequency is connected to the drain terminal 2 of the FET 1. A strip line 5 is connected to the gate terminal 4 of the FET 1, and the strip line 5 is further terminated with a dummy resistor 6. Reference numeral 7 denotes a dielectric resonator, which is arranged so as to be coupled to the strip line 5. A strip line 9 is connected to the source terminal 8, and a dielectric resonator 7
The output of the oscillator oscillated at the resonant frequency is taken out from the strip line 9 and supplied to the load. 10
is a low-pass filter for the bias supply circuit, and is composed of a high impedance line and a low impedance line. 11 is a resistor, one end of which is connected to the low impedance line of the low pass filter 10, and the other end connected to the capacitor 12.
And the bias power supply is connected to the FET through resistor 11.
1 is supplied.

Problems to be Solved by the Invention Generally, the gain of a transistor increases as the frequency decreases, so parasitic oscillations often occur at frequencies lower than the oscillation frequency of the oscillator. In FIG. 8, if the reflection coefficient when looking from the gate terminal 4 of FET 1 to the FET 1 side is S ₁₁ and the reflection coefficient when looking from the gate terminal 4 to the dummy resistor 6 side is Γ _R , then S ₁₁ ×Γ _R = 1...(1 ) Oscillation is performed when the following conditions are satisfied. The reflection coefficient Γ _R is only near the resonance frequency of the dielectric resonator 7 |Γ _R |1
If the resonant circuit on the gate terminal 4 side is set so that |Γ _R |0 at other frequencies, the oscillator shown in FIG. 8 stably oscillates at the resonant frequency of the dielectric resonator 7. However, the dummy resistor 6 has a reflection coefficient |Γ|
However, at other low or high frequencies, it is not necessarily configured to be |Γ|0. For example, 50Ω
An example of this is a dummy resistor consisting of a resistor and an open-ended 1/4 wavelength line. With a dummy resistor composed of a 50Ω resistor and a short-terminated low-pass filter containing a 1/4-long line with an open terminal, if the operating frequency is 11 GHz, then in the frequency range of 1 GHz or less or 7 to 14 GHz, |Γ| It shows characteristics close to 0, but 2
In the range of ~6 GHz, it exhibits characteristics close to |Γ|1.
On the other hand, since FET1 has the characteristic that the gain increases as the frequency decreases,
The reflection coefficient |S′ ₁₁ | for a small signal looking at the FET1 side is
Shows negative resistance down to low frequencies, |S′ ₁₁
|>1. Furthermore, the low-pass filter 10 also makes the drain terminal 2 more likely to be grounded at high frequencies at frequencies below the operating frequency, which causes |S' ₁₁ | to further increase. Therefore, the characteristics of the dummy resistor 6 come to satisfy the condition of S ₁₁ ×Γ _R =1 even at frequencies close to |Γ|1, which causes parasitic oscillation. And that parasitic oscillation is likely to occur at a frequency somewhere in the range of 3 to 5 GHz.

The present invention solves the conventional problem of parasitic oscillation as described above, and the FET or bipolar transistor's gate terminal or base terminal
Or, create a microwave oscillator that prevents parasitic oscillation by reducing the small signal reflection coefficient |S′ ₁₁ | looking at the bipolar transistor side at the parasitic oscillation frequency, eliminating negative resistance, or weakening negative resistance. The purpose is to provide

Means for Solving the Problems In the present invention, a resistor whose one end is connected to a low-pass filter for a bias supply circuit composed of a high impedance line and a low impedance line has a length that causes parasitic oscillation. This is a connection of open-ended strip lines at 1/4 wavelength of the frequency.

Effect With the above configuration, the impedance seen from the drain or collector terminal of the FET or bipolar transistor to the low-pass filter side for the bias supply circuit can satisfy the matching condition around the parasitic oscillation frequency, and small signal reflection Coefficient｜
S′ ₁₁ | can be made small at that frequency,
It prevents parasitic oscillation by eliminating or weakening the negative resistance of the impedance when looking at the FET or bipolar transistor side from the gate or base terminal of the FET or bipolar transistor.

Examples Examples of the present invention will be sequentially described below. Although FIG. 1 shows one embodiment of the present invention, the same parts as in FIG. 8 are given the same numbers and will be explained.

The drain terminal 2, gate terminal 4, and source terminal 8 of the FET 1 are connected to a strip line 3 whose length is approximately 1/4 wavelength of the oscillation frequency with an open end, a strip line 5 terminated with a dummy resistor 6, and a strip line 5 that is connected to the load. A strip line 9 for supplying oscillation output is connected. Reference numeral 7 denotes a dielectric resonator, which is arranged so as to be coupled to the strip line 5. A low-pass filter 10 for a bias supply circuit composed of a high impedance line and a low impedance line is connected to the strip line 3, and a resistor 11 is connected to the strip line 3.
A bias power supply is supplied to FET1 via. An open-ended strip line 13 is connected to one end of the resistor 11 connected to the bias power supply side and has a length of about 1/4 wavelength of the frequency of parasitic oscillation that occurs in the conventional example. The capacitor 12 is a capacitor that serves not only as a direct current blocker but also as a high frequency bypass.

In the embodiment shown in FIG. 1, the reflection coefficient |Γ _d | of the impedance viewed from the drain terminal 2 of the FET 1 to the low-pass filter 10 side becomes small at the parasitic oscillation frequency. This is because the bias power supply side terminal of the resistor 11 is connected to the resistor 11 due to the open-ended strip line 13 (regardless of the state of impedance seen from the ground point side from the terminal of the capacitor 12 connected to the resistor 11), and the parasitic oscillation frequency is high frequency. This is because the resistor 11 operates as a damping resistor since it is short-circuited. Therefore, from gate terminal 4 of FET1
The reflection coefficient S' ₁₁ for a small signal looking at the FET 1 side also eliminates negative resistance at the parasitic oscillation frequency or weakens the negative resistance, thereby preventing parasitic oscillation.

Here, the reason why the small signal reflection coefficient |S′ ₁₁ | becomes smaller as the above-mentioned reflection coefficient |Γ _d | becomes smaller will be explained in more detail.

FIG. 2 is a block diagram for explaining each coefficient, and is a circuit in which a strip line 20 of length l is connected to the drain terminal 2, and a load resistor 21 is connected to the terminal end of the strip line 20. In the circuit shown in Figure 2, the small signal reflection coefficient when looking from the gate terminal 4 of FET 1 to the FET 1 side |
FIG. 3 is a computer simulation showing the relationship between S′ ₁₁ | and the reflection coefficient |Γ _d ′| when looking from the drain terminal 2 of the FET 1 to the resistor 8 side. however,
The length l of the strip line 5 is the resistance value R of the resistor 8 =
It is selected so that |S′ ₁₁ | shows the maximum value near the frequency = 4.25 GHz when ∞. The reason why the length l of the strip line 5 was selected in this way is that
In the figure, when the oscillation frequency was 11 GHz, parasitic oscillation occurred at approximately 4 GHz.In response to this, when R = ∞ (corresponding to the open end of the strip line 20) in the circuit configuration shown in Figure 2, This is to ensure that the negative resistance value is greatest near 4 GHz.

As is clear from FIG. 3, as |Γ _d ′| decreases, |S′ ₁₁ | or the magnitude of the negative resistance decreases. This can be seen in the example shown in Figure 1.
If the reflection coefficient |Γ _d | viewed from the drain terminal 2 of FET 1 to the low-pass filter 10 side is reduced,
This means that parasitic oscillations that occur at approximately 4 GHz can be prevented.

Note that the low-pass filter 10 does not cut off the parasitic oscillation frequency (approximately 4 GHz in the above example). For example, when the pass characteristic |S ₂₁ |dB is actually measured using a circuit as shown in FIG. 4, it becomes as shown in FIG. That is, although it is attenuated to some extent, the terminal 40
The signal of the parasitic oscillation frequency is sufficiently transmitted to the strip line 13 (in FIG. 1).

Furthermore, if the oscillation frequency is 11 GHz (described above), the signal at this oscillation frequency is cut off by the low-pass filter 10 and does not reach the terminal 40 in FIG. The resistor 11 also has no effect on the oscillation operation. On the other hand, the signal at the parasitic oscillation frequency (approximately 4 GHz) is transmitted to the resistor 11 as described above, and the signal is attenuated by the resistor 11 (the aforementioned damping operation), so that the parasitic oscillation is suppressed.

FIG. 6 compares the reflection coefficient |Γ _d | viewed from the drain terminal 2 of the FET 1 to the low-pass filter 10 side between the conventional example (FIG. 8) and the embodiment shown in FIG. Resistance value R of resistor 11 and strip line 1
It is understood that parasitic oscillation can be prevented by appropriately selecting the line length of No. 3. If the oscillation frequency is
When a 11GHz oscillator is configured as in the conventional example, approximately
Parasitic oscillation occurred at 4 GHz, but in this example, it has been confirmed that if the resistance value R of the resistor 11 is selected in the range of several Ω to about 60 Ω, the parasitic oscillation at about 4 GHz is stopped.

In FIG. 6, in this embodiment, there is a place near 3 GHz where the impedance reflection coefficient |Γ _d | when looking from the drain terminal 2 to the low-pass filter 10 side is large. If we look at this using the small signal reflection coefficient S′ ₁₁ or negative resistance, it similarly shows a relatively large value near 3 GHz (｜S′ ₁₁
|=3.5~5dB). (In the conventional example shown in Figure 8, the small signal reflection coefficient S' ₁₁ has a similarly large value around 4.2 GHz.) However, in order for parasitic oscillation to occur at 3 GHz, S ₁₁ ×Γ The condition _R = 1 must be satisfied. In order for this condition to hold, the length of the strip line 5 on the gate terminal 4 side must be approximately 1/4 at 3 GHz.
Conditions are required, such as the wavelength and the characteristics of the dummy resistor 6 being very poor at 3 GHz. This example (first
In the conventional example (Fig. 8) shown in Fig. 8, parasitic oscillation occurred at about 4 GHz, so it is considered that S ₁₁ ×Γ _R =1 is established at this frequency of about 4 GHz. Therefore, unless the length of the strip line 5 or the value of the dummy resistor 6 is changed, parasitic oscillation will not occur even if only the negative resistance value becomes slightly large near 3 GHz.

As described above, in this embodiment, the configuration is simple because it is sufficient to simply add the strip line 13.
Moreover, it has the advantage that only a simple modification of the configuration of the entire oscillator is required.

In addition, although the case where parasitic oscillation occurs at approximately 4 GHz has been explained above, if the parasitic oscillation frequency becomes another when tuning to another oscillation frequency, the line length of the strip line 13 should be adjusted to that parasitic oscillation frequency. Just change it accordingly, and since this line length change has nothing to do with the desired oscillation frequency,
It also has the advantage of easily suppressing parasitic oscillations. Furthermore, the usable range of resistor 11 is from several ohms to approx.
Since it has a wide range of up to 60Ω, it also has the advantage that the resistance value of the resistor 11 can be selected in accordance with the magnitude of the voltage of the bias power supply.

FIG. 7 shows another embodiment of the present invention, and the same parts as in FIG. 1 are given the same numbers and will be described. The structure is completely the same as that in FIG. 1 except that a feedthrough capacitor 14 is used in FIG. 7 instead of the capacitor 12 in FIG. 1. Since the effect of the strip line 13 and resistor 11 on parasitic oscillations is exactly the same as in FIG. 1, the embodiment of FIG. 7 has the same advantages as the embodiment of FIG. 1.
In particular, in the embodiment shown in Fig. 7, the feedthrough capacitor 1 is used as a DC blocking and high frequency bypass capacitor
4, it has the effect of eliminating fluctuations in the oscillation frequency due to movement of the lead wire leading from the bias power supply to the feedthrough capacitor.

In the embodiment described above, as an oscillation element,
Although the explanation was made using FET, as an oscillation element,
Needless to say, a bipolar transistor may also be used. In that case, the drain in the description corresponds to the collector, and the gate corresponds to the base.

Effects of the Invention As described above, according to the present invention, as a measure to prevent parasitic oscillation, parasitic oscillation at a wide range of frequencies can be prevented by simply adding an open-ended strip line with a quarter wavelength of the parasitic oscillation frequency. This has the effect of easily dealing with the situation. Moreover, the range of use of the oscillator's drain or collector bias resistor, which acts as a damping resistor to prevent parasitic oscillation, is wide, from several Ω to about 60 Ω. It also has the effect of allowing you to choose the size.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a microwave oscillator according to an embodiment of the present invention, Fig. 2 is a block diagram of a circuit for explaining each coefficient, and Fig. 3 is a view of the drain bias circuit side from the drain terminal of the FET. reflection coefficient of impedance |Γ _d ′| and small signal reflection coefficient |
S' ₁₁ | characteristic diagram, Figure 4 is a configuration diagram for explaining the low-pass filter, Figure 5 is its low-pass characteristic diagram, Figure 6 is the frequency characteristic diagram of |Γ _d |, and Figure 7 is The figure is a block diagram of another embodiment, and FIG. 8 is a block diagram of a conventional example. 1...FET, 2...Drain terminal, 4...Gate terminal, 6...Dummy resistor, 7...Dielectric resonator, 10...Low pass filter, 11...Resistor,
12... Capacitor, 13... Open terminated strip line having a length of 1/4 wavelength of the parasitic oscillation frequency.

Claims (1)

[Scope of Claims] 1. A first transmission line with an open end and a length of about 1/4 wavelength of the oscillation frequency is connected to the drain or collector terminal of the field effect transistor or bipolar transistor, and the field effect transistor or bipolar transistor A resonant circuit using a dielectric resonator is added to the gate or base terminal of the first transmission line to configure a drain or collector-grounded microwave oscillation circuit. One line with four wavelengths and high characteristic impedance, and one line with length approximately 1/4 wavelength of the oscillation frequency and low characteristic impedance.
Connect one end of a low-pass filter consisting of one end to the other end of the low-pass filter, connect one end of the drain or collector resistor to the other end of the low-pass filter, and connect the other end of the drain or collector resistor to the length of the microwave oscillation filter. A second open-ended transmission line is connected at approximately 1/4 wavelength of the unnecessary oscillation frequency of the circuit, and a bias voltage of the field effect transistor or bipolar transistor is applied from the other end of the drain or collector resistor. A microwave oscillator featuring: 2. The resistance value of the drain or collector resistor is set so that the reflection coefficient of the impedance when looking at the low-pass filter side from the drain or collector terminal of the field effect transistor or bipolar transistor is small at the unnecessary oscillation frequency of the microwave oscillation circuit. A microwave oscillator according to claim 1, characterized in that: