JPS5940708A - Microwave oscillator - Google Patents

Abstract

PURPOSE:To prevent parasitic oscillation, by connecting a strip line with open end and having 1/4 wavelength of parasitic oscillation frequency in length, to other end of a resistor one end of which is connected to a low-pass filter for bias supply circuit comprising a high impedance line and a low impedance line. CONSTITUTION:The strip line 13 with open termination and having about 1/4 wavelength of a frequency of parasitic oscillation generated conventionally in length is connected to one end of a resistor 11 connected to a bias power supply. A capacitor 12 is a capacitor used for DC blocking and high frequency by-pass. The reflecting coefficient ¦GAMMAd¦ of an impedance viewed from a drain 2 of an FET1 toward a low-pass filter 10 is decreased in the parasitic oscillation frequency. This is because a terminal at bias power supply side of the resistor 11 is short-circuited in terms of high frequency in the parasitic oscillating frequency by the strip line with open termination and the resistor 11 acts like a damping resistor. Thus, the parasitic oscillation is prevented for the reflecting coefficient S'11 at a small signal viewing the FET1 from a gate 4 of the FET1 by eliminating the load resistance at the parasitic frequency or weakening the load resistance.

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.

Conventional Structure and Its Problems FIG. 1 shows an example of the structure of a conventional microwave oscillator using a field effect transistor (FET).

1 is a FET, and the drain terminal 2 of FET 1 is a strip line 3 whose length is approximately three wavelengths of the oscillation frequency and whose ends are open.
is connected. A strip line ff%5 is connected to the gate terminal 4 of FET1, and an IJ tube line 6 is connected to the gate terminal 4 of FET1.
is terminated with a dummy resistor 6. A dielectric resonator 7 is arranged so as to be coupled to the strip line 6. A strip line 9 is connected to the source terminal 8, and the output of the oscillator oscillated at the resonant frequency of the dielectric resonator 7 is taken out from the strip line 9 and supplied to the load. 1° is a low-pass filter for the bias supply circuit, which 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 1o, and the other end connected to the capacitor 1.
2 is connected.

A bias power source is supplied to the FET 1 via a resistor 11.

Since the gain of a transistor generally increases as the frequency decreases, parasitic oscillations often occur at frequencies lower than the oscillation frequency of the oscillator. In FIG. 1, the reflection coefficient when looking from the gate terminal 4 of FET 1 to the FETI side is 811. If the reflection coefficient when looking from the gate terminal 4 to the dummy resistor 6 side is PR, then 811×FR-1...
...Oscillation is performed while satisfying the condition (1). The reflection coefficient FR becomes l/'n1 = 1 only near the resonance frequency of the dielectric resonator 7, and +7 at other frequencies.
If the resonant circuit on the gate terminal 4 side is set so that R1≧0, the oscillator shown in FIG. 1 stably oscillates at the resonant frequency of the dielectric resonator 7. However, the dummy resistor 6 is configured so that its characteristics are 1rl=0 in the band around the frequency used, but it is not necessarily configured so that 1rl=o at other low or high frequencies. There is no guarantee that it will be done. For example, a dummy resistor is made up of a 60Ω resistor and a broken wavelength line with an open end. If the operating frequency is 11 GHz, a dummy resistor composed of a 60Ω resistor and an open-ended blue wavelength line exhibits characteristics close to 1Fl=o below IGHz or in the frequency range of 7 to 14 GHz, but in the range of 2 to 6 GHz. Then Irl Sa1
It shows characteristics close to . On the other hand, FET! has a characteristic that the gain increases as the frequency decreases, so the reflection coefficient Is'1 for a small signal looking from the gate terminal 4 to the FET 1 side is
11 shows negative resistance down to low frequencies,
Is'111>1. Therefore, the characteristics of the dummy resistor 6 come to satisfy the condition of S11×rR=1 even at a frequency close to 17''l=1, which causes parasitic oscillation.The parasitic oscillation is 3~5αh It is likely to occur within the range of

OBJECTS OF THE INVENTION The present invention solves the conventional parasitic oscillation problems as described above, and provides a small signal reflection coefficient of 15'1. It is an object of the present invention to provide a microwave oscillator in which parasitic oscillation is prevented by reducing I at the parasitic oscillation frequency and eliminating or weakening negative resistance.

Structure of the Invention In the present invention, one end of a resistor is connected to a low-pass filter for a bias supply circuit composed of a high impedance line and a low impedance line, and the other end is connected to a resistor whose length is equal to the wavelength of the parasitic oscillation frequency. By connecting an open-ended strip line at , the impedance when looking from the drain or collector terminal of the FET or bipolar transistor to the low-pass filter side for the bias supply circuit is
Matching conditions should be satisfied around the parasitic oscillation frequency.

The gate of the FET or bipolar transistor also eliminates the negative resistance of the impedance when looking from the base terminal to the pFET or bipolar transistor side, but it weakens the negative resistance and prevents parasitic oscillation.

DESCRIPTION OF EMBODIMENTS Below, embodiments of the present invention will be sequentially explained. FIG. 2 shows one embodiment of the present invention, and the same parts as in FIG. 1 are given the same numbers and will be explained.

The drain terminal 2, gate terminal 4, and source terminal 8 of FET 1 are connected to an IJ tube line 3, a strip line 5 terminated with a dummy resistor 6, and a load. A strip line 9 is connected to supply oscillation output to ◇7 is a dielectric resonator,
It is arranged so as to be coupled to the strip line 5. A low-pass filter 1o for a bias supply circuit composed of a high impedance line and a low impedance line is connected to the strip line 3, and bias power is supplied to the FET 1 via a resistor 11.

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 approximately equal to the wavelength of the frequency of parasitic oscillation occurring 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. 2, the reflection coefficient IF,ll of the impedance viewed from the drain terminal 2 of the FET 1 toward the low-pass filter 1o becomes small at the parasitic oscillation frequency. This is because the bias power supply side terminal of the resistor 11 due to the open-terminated strip line 13 (regardless of the impedance state when looking from the terminal of the capacitor 12 connected to the resistor 11 to the ground point side), at the parasitic oscillation frequency. This is because the damper resistor 11, which is short-circuited at high frequencies, operates as a damping resistor. Therefore, the reflection coefficient S'11 for a small signal looking from the gate terminal 4 of FET 1 to the FET 1 side is such that the negative resistance is eliminated or weakened at the parasitic oscillation frequency, and parasitic oscillation is prevented. be.

FIG. 3 compares the reflection coefficient l/', 11 when looking from the drain terminal 2 of the FET 1 to the low-pass filter 10 side between the conventional example and FIG. It is understood that parasitic oscillation can be prevented by appropriately selecting the resistance value R of the resistor 11 and the line length of the strip line 13. For example, the oscillation frequency is 1
When a 1 GHz oscillator is configured as in the conventional example,
Parasitic oscillation occurred at about 4 GHz, but it was confirmed that if the configuration was reconfigured as shown in Figure 2 and the resistance value R of resistor 11 was selected in the range of several ohms to about 6 ohms, the parasitic oscillation at about 4 GHz stopped. There is.

The embodiment shown in FIG. 2 has the advantage that the structure is simple because it is only necessary to add the strip line 13, and furthermore, the structure of the entire oscillator requires only a simple modification. In addition, the strip line 13
Since the line length can be easily changed, it also has the advantage of being able to easily deal with parasitic oscillations of a wide range of frequencies. Furthermore,
Since the range in which the resistor 11 can be used is wide, from several Ω to about 60 Ω, there is also an 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. 4 shows another embodiment of the present invention, and the same parts as in FIG. 2 are given the same numbers and will be described. Capacitor 1 in Figure 2
The structure is exactly the same as that in FIG. 2 except that a feedthrough capacitor 14 is used in place of capacitor 2 in FIG. The effect of the strip line 13 and the resistor 110 on parasitic oscillation is the second
The embodiment of FIG. 4 has the same advantages as the embodiment of FIG. 2, since it is exactly the same as that of FIG.

In particular, in the embodiment shown in FIG. 4, since the feedthrough capacitor 14 is used as a capacitor for direct current blocking and high frequency bypass, fluctuations in the oscillation frequency due to movement of the lead wire leading from the bias power supply to the feedthrough capacitor are eliminated. has.

In the embodiments described above, an FET is used as the oscillation element, but it goes without saying that a bipolar transistor may also be used as the oscillation element.

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 of a wide range of frequencies can be easily prevented by simply adding an open-ended strip line with a wavelength of % of the parasitic oscillation frequency. It has the effect of being able to deal with. 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 approximately 6 Ω. This also has the effect of allowing you to choose the size of.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional microwave oscillator;
The figure is a configuration diagram of a microwave oscillator according to an embodiment of the present invention, and Figure 3 is an impedance reflection coefficient IFJ1 when looking from the drain terminal of the FET to the drain bias circuit side.
FIG. 4 is a configuration diagram of a microwave oscillator in another embodiment of the present invention. 1...FET, 2...Drain terminal,
4... Gate terminal, 6... Dummy resistor, 7... Dielectric resonator, 10... Low pass filter, 11...・Resistance, 12...
- Capacitor, 13... Open-terminated strip line having a length of % wavelength of the parasitic oscillation frequency. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
To the load Figure 2 To the load Figure 3 Frequency (open 2)

Claims (2)

[Claims] (1) A first open-ended transmission line with a length of about three wavelengths of the oscillation frequency is connected to the drain or collector terminal of the field effect transistor or bipolar transistor,
A resonant circuit using a dielectric resonator is added to the gate or base terminal of the field effect transistor or bipolar transistor to configure a drain or collector-grounded microwave oscillation circuit, and a low-pass oscillator is connected to the first transmission line. One end of the filter is connected to the other end of the low-pass filter, and one end of the drain or collector resistor is connected to the other end of the drain or collector resistor, the length of which is approximately 3 times the unnecessary oscillation frequency of the microwave oscillation circuit.
A microwave oscillator, characterized in that a second open-ended transmission line is connected to the wavelength, and a bias voltage of the field effect transistor or bipolar transistor is applied from the other end of the drain or collector resistor. (2) Set the resistance value of the drain or collector resistor 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: