JPS60153613A - Microwave amplifier circuit - Google Patents

Abstract

PURPOSE:To prevent oscillation at impedance mismatching with a device of the front stage by selecting a loss of a feedback circuit of an amplifier element as a value not representing any feedback operation at a band of a microwave signal. CONSTITUTION:The polarized plane of a microwave signal incoming to a primary radiator 1 is selected by a selector 2, and further converted into a coaxial mode by a waveguide-coaxial converter 3, amplified by the amplifier element 7 and transmitted from an output terminal 6. The loss of the feedback circuit 8 in a band W of the microwave signal to be amplified is increased and the circuit reaches a state similar to the absence of the feedback circuit, and the incoming microwave signal at a terminal 5 is amplified by the element 7 and transmitted from a terminal 6. On the other hand, the loss of the circuit 8 is small at a band lower than the band W and shows the feedback operation. As a result, the input impedance at the terminal 5 in case of impedance mismatching is brought into a region without any negative resistance and the element 7 attains stable amplification without causing any oscillation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microwave amplification circuit for amplifying microwave signals.

In a conventional microwave amplification circuit, a microwave amplification element provided between an input terminal and an output terminal amplifies the microwave that enters the input terminal, and outputs it from the output terminal. However, when a pre-stage device with impedance mismatching is connected to the input terminal, the operating state of the amplifying element becomes unstable, causing oscillation.

Therefore, the present invention is designed to eliminate the above-mentioned problems, and it is a matter of theory that if the input terminal and the preceding equipment connected thereto are in a matching order, the microwave signal can be properly amplified.
It is an object of the present invention to provide a microwave amplification circuit which can properly amplify a microwave signal coming from a preceding device even if the input terminal and the preceding device are mismatched.

Below, drawings showing embodiments of the present application will be described.

In FIG. 1, l is a primary radiator, which is an example of a nine-aperture conical horn installed at the focal point of a parabolic antenna reflector. 2 is a polarization selector that converts the microwave signal sent as circularly polarized, vertically polarized, horizontally polarized, etc. into a linearly polarized signal with a polarized wave in a direction that is easier to process in the subsequent stage. It is for choosing. 3 indicates a waveguide-coaxial converter. 4 indicates a microwave amplifier circuit, and 5 and 6 indicate its input terminal and output terminal.
.

Reference numeral 7 indicates an amplifying element, which is a low-noise FET for microwaves. 8 indicates a feedback circuit. In this feedback circuit, 9
1 is a distributed constant line, 10 is a resistor, and a series circuit of these is connected between an input terminal 5 and an output terminal 6. U indicates a capacitor. The relationship between the distributed constant line 9 and the capacitor (2) is such that their values are determined so that they have a common point A in the band W of the microwave signal to be amplified as shown in FIG. is selected to have a size that damps the sharpness of the resonance so that the loss of the feedback circuit 8 becomes sufficiently large in the band W so that the feedback circuit 8 does not substantially exhibit a feedback effect, or The value of the above-mentioned band wjl is selected so that in a low band, the loss of the feedback circuit 8 becomes small and the circuit 8 exhibits a feedback effect. For example, 800 to 500Ω is used as the second value.

With the above configuration, the polarization plane of the microwave signal entering the primary radiator 1 is selected by the selector 2, and the waveguide mode is further converted into a coaxial mode by the waveguide-coaxial converter 3. Ru. The converted signal enters the input terminal 5, is amplified by the amplification element 7, and is sent from the output terminal 6 to the subsequent amplifier.

When amplifying the microwave signal as described above, input terminal 5
The signal can be stably amplified even if the impedance of the converter 3 and the impedance of the converter 3 are matched or not matched. That is, within the band W of the microwave signal to be amplified, the loss of the feedback circuit 8 becomes large, so that the state is as if it were not present, and the microwave signal entering the input terminal 5 is passed through the amplification element. 7 and sent out from the output terminal 6. Furthermore, in a band lower than the above-mentioned band W, the loss of the feedback circuit 8 becomes small as described above, so that the feedback circuit 8 exhibits a feedback effect. As a result, the input impedance of the input terminal 5 can be ensured in a region that is not a negative resistance even in the case of impedance matching, which is thermal theory, and even in the case of mismatching. Therefore, the amplification element 7
is maintained in a state where it exhibits a stable amplification effect without causing oscillation. Thereby, signals within the band W can be stably amplified.

Next, FIG. 3 shows the relationship between frequency and noise figure of the amplifier circuit having the above configuration. As is clear from this figure, within the band W, the noise figure is a very small value of about tdB, and the microwave signal can be amplified with extremely low noise.

Next, Figure 1 is a Numis chart showing the input impedance characteristics of the power terminal 5. 2) is the characteristic when the feedback circuit 8'' is connected, and 2) is the characteristic when the feedback circuit 8 is removed. As is clear from the figures showing the characteristics of each case, the input impedance when no feedback circuit is connected is (T).
As shown in , there is a part that protrudes from the circle C indicating the positive resistance region, that is, the stable region, and the amplifier circuit becomes unstable at that point. ), the input impedance falls within the above circle C- no matter what the 0 frequency is.

From this, it can be understood that in the amplifier circuit connected to the feedback circuit 8-, the human-powered microwave signal can be stably amplified. ' □ Next, FIG. S shows the structure of the microwave amplifying circuit 4 substantially unchanged. In the figure, 14 is a circuit board with conductive foils 16 on the front and back surfaces of an insulator 150. It is constructed using a peephole equipped with 17. Furthermore, as the insulating material, a material with low dielectric loss, such as a fluororesin, is used. Further, the conductor foil 16 on the front surface constitutes circuit conductors of various shapes as shown in the drawings, and the conductor foil 16 on the back surface is provided over the entire surface and constitutes a ground conductor. Next, in the circuit conductor constituted by the conductor foil 16 on one surface, k and 19 are electrical terminals to which +8 and -0,5 to -8 are supplied, respectively. Add.

Reference numeral 21 denotes a microwave choke, which has a length about 1/4 wave for the signal having the frequency of the band W used.

ρ and 23 are capacitors that allow microwaves to pass through and block direct current, and are made of Ashichip capacitors. The stub is a stub with a good N in the used band W.
The length is adjusted to obtain F characteristics. The device is a stub and is used to adjust the output impedance. Also, the amplification element 7 is used by a microwave FET.
G and drain 7D are connected to the circuit conductor on the surface of the board by saw 77.
Reference numerals 8 and 8 are respectively connected to ground conductors on the back side through through holes drilled in the substrate. The capacitor 11 is connected to the circuit conductor 16
A capacitor having a capacitance of 1 to 2.5 pF is formed between the two and a ground conductor 17 on the back surface. I is a capacitor that allows microwaves to pass through and blocks direct current from the power supply. For example, a chip capacitor of about 10 pF is used. The distributed constant line 9 has a characteristic impedance of 100~
120Ω2, (thickness 0.15MjI), usage band (4,
2GH2), the length is about 1/4 wavelength, and the length is about 114g).

(The shortening rate is about 0.6.) Next, Fig. 6 shows a different embodiment of the present application, and shows different examples of devices connected to the input terminal, as well as a distributed constant line and a resistor in the feedback circuit. This shows examples of different positional relationships. In the figure, 31 is a primary radiator, which is an example of a dipole with a reflector installed at the focal point of a parabolic antenna reflector.

The wings indicate a balanced-to-unbalanced converter.

In such a configuration, a weak level linearly polarized microwave signal sent from a broadcasting satellite is received by the primary radiator 31, and the balanced state becomes unbalanced at the converter ~. converted. The unbalanced signal is at input terminal 5e.
and is amplified by the amplification element 7e in the same manner as in the above case. The amplified microwave signal is then sent out from the output terminal 6e.

It should be noted that the same reference numerals as those in the previous figure L1 are given the alphabet e to the parts that are considered to have the same or equivalent configuration as those in the previous figure in terms of function, and redundant explanations are omitted.

(Also, the same concept will be used in the next version, and the redundant explanation will be omitted by adding the letter f.) Next, FIG. This is an example. In the figure, the ground conductor provided on the front surface of the board 14f is connected to the ground conductor 1 on the back side through the through hole/I/35.
7 Connected to f.

1 is a capacitor in the feedback circuit, which is the same as the capacitor 11 shown in FIG. 1, and is a static capacitor.

As described above, according to the present invention, when there is an input signal of a weak signal μ at the input terminal 5, the signal can be amplified with low noise by the amplification element 7 and outputted, and the noise level is low and the signal level is increased. It has the advantage of being able to obtain a signal.

Moreover, when a pre-stage device is connected to the input terminal 5 in order to provide the above input signal, it goes without saying that if the impedance of the pre-stage device matches the impedance seen from the input terminal 5 to the amplification element 7, then it is matched. Both have the feature of being able to perform low-noise amplification as planned in the design, even when not in use. That is, even if the feedback circuit 8 is provided in parallel to the amplifying element 7, the loss of the feedback circuit 8 increases in the band of the microwave signal that needs to be amplified, resulting in a state similar to that without it, and the impedance increases. The expected amplification can be achieved regardless of matching or mismatching, and the loss of the feedback circuit 8 is small in the above-mentioned band as well as in the lower band 9, which exhibits a feedback effect and causes the impedance of the input terminal to become negative. If the impedance of the preceding device matches the impedance of the input terminal, even if it does not match, oscillation can be prevented, and stable amplification in the above band can be achieved. It has the effect of ensuring the condition.

[Brief explanation of drawings]

The drawings show an embodiment of the present application; Fig. 1 is a block circuit diagram, Fig. 2 is a graph showing the loss of the feedback circuit, Fig. 3 is a graph showing the noise figure, and Fig. 1 shows the input impedance characteristics. Smithcher 1, Figure S is the actual diagram of the amplifier circuit,
FIG. 6 is a block circuit diagram showing a different embodiment, and FIG. 7 is a block diagram showing a different circuit. 5... Input terminal, 6... Output terminal, 7... Amplifying element, 8... Feedback circuit, 9... Distributed constant line, lO.
...Resistor, U...Capacitor. 1st t! 1 Figure 5 Figure 2' Figure 3. Figure 4 (8) e Figure 7

Claims (1)

[Claims] Between the input terminal for connecting the pre-stage equipment and the output terminal for signal output, an amplification element is connected that amplifies the microwave signal coming into the input terminal and outputs it from the output terminal. In the amplifier circuit, a feedback circuit consisting of a series circuit of a distributed constant line and a resistor is connected between the input side and the output side of the amplifying element, and the connection point between the distributed constant line and the resistor is connected via a capacitor. Furthermore, the relationship between the distributed constant line, resistor, and capacitor is such that the distributed constant line and the capacitor have a resonance point within the band of the microwave signal to be amplified, and the resistor damps the sharpness of the resonance. Therefore, the loss of the feedback circuit is so high that it does not substantially exhibit a feedback effect within the above band, and is high enough to exhibit a feedback effect so that the impedance of the input terminal does not become a negative resistance in a band lower than the above band. A microwave amplifier circuit characterized in that the loss is determined to be low.