JPS5860809A - High frequency amplifier - Google Patents

Abstract

PURPOSE:To improve wide band characteristics by inserting a circuit with low- pass characteristics between the isolation terminals of a preamplifier and a post amplifier, and thus coupling both together. CONSTITUTION:Balanced amplifiers 20 and 21 are connected in two stages, and a circuit with low-pass characteristics, e.g. a low-pass filter 24 consisting of an L and a C is connected between the output-side isolation terminal 22 of the preamplifier 20 and the isolation terminal 23 of the input-side coupler of the post-amplifier 21. The terminals 22 and 23 are connected mutually by the low- pass filter 24 in a low band which is not in the band of the coupler, so a microwave of low frequency inputted to the input terminal 25 of the preamplifier 20 is outputted to the terminal 22, but inputted to the terminal 23 of the amplifier through the low-pass filter 24 to appear at the output terminal 26 of the amplifier 21.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a high frequency amplifier C with broadband operating characteristics:
related.

Conventionally, amplifiers with broadband characteristics of 0°5 octave or more in the microwave frequency band ζ2 have mainly been
Balanced amplification gain as shown in Figure 81 is used. That is, input and output broadband coupler 1.
2 and two V-end amplifiers 3.4.

In addition, as broadband couplers 1 and 2, 182
As shown in the figure, an interdigital coupler is mainly used because the f-2 type is small and relatively easy to manufacture.

When a microwave is input to the input terminal 5 of this hybrid coupler, an output wave appears at the terminal 6.1 and is not output to the Rayon terminal 8. The phase of the output wave appearing at terminal 1 is delayed by 90' from the phase of the output wave appearing at terminal 6 (=
If the reflection coefficients of the loads connected to terminals 6 and 7 are equal, there will be a mismatch at the input tin of amplifier 1.4, and even if the reflected waves generated there are input again to terminals 6 and 7, they will not be output to terminal 5. The reflection coefficient at terminal 5 can be kept small by connecting terminal J (2 non-reflective terminations). Bifurcation C: When amplifiers are connected in multiple stages, the amplifier output If the reflection coefficient is large, multiple reflections occur between stages, resulting in deterioration of gain flatness within the band and oscillation, but balanced amplifiers have the advantage of being easy to connect in multiple stages for the above-mentioned reasons.

By the way, terminals 5 and 6 of the coupler shown in FIG. Or 7 and 8
The frequency characteristic of the degree of coupling I S between 651" and +8871" is as shown by curve 1 in FIG. 3, and the degree of coupling approaches O outside the passband B.

Also, terminals 5 and 7. or the degree of conductivity 1 between terminals 6 and 8
875 and 18861' become close to 1 outside band B, as shown by the curve in FIG. Therefore, when a microwave outside band B is incident on the input terminal 5 of the balanced amplifier shown in diagram gIp11, the incident wave is outputted to the terminal 7, passes through the single-ended amplifier 4, and passes through the output side coupler's input terminal 9.
C output and resistor terminated 10C: Absorbed, the gain of the balanced amplifier is significantly reduced outside the band B of the coupler.

As mentioned above, the gain of conventional balanced amplifiers was limited by the band C of the output hybrid coupler, so the 1 to 1.5 octave band was the limit. In order to widen the bandwidth of the device, there is a method of making it double-staged as shown in Fig. 4, but this method has the disadvantage that it becomes large in size and is not suitable for microwave integrated circuits that aim to be miniaturized.

The present invention eliminates the above-mentioned drawbacks and the conventional /47
The purpose of the present invention is to provide a high-frequency amplifier with the same size and wider bandwidth as an amplifier.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

As shown in Figure 15, the balanced amplifier 20゜2]
A circuit having a low-pass characteristic, for example, 0
A low-pass filter 24 composed of the following is connected. In this case, since the input and output impedances of the low-pass filter are high within the band of the coupler, it operates in the same way as a conventional balanced amplifier. Further, 2, outside the band of the coupler, the low-pass filter 242 connects the isolation terminal 22 and zs'bs in a low band, so the low-frequency microwaves irradiated by the input terminal 254 of the preamplifier 20 are The output from the isolation terminal 22 passes through the low-pass filter 24 and is input to the output terminal 23 of the downstream amplifier, and is output to the output terminal 26 of the downstream amplifier. (transistors, FETs, etc.) have the property of increasing their gain in the low frequency range, so the gain of the amplifier at low frequencies may increase.
In the amplifier shown in Fig. 5, a beam of low-frequency microwave power is absorbed by the resistor terminals 2r and 28g' connected to the isolation pins 22 and 23, so the gain in the low frequency band is the same as the gain in the microwave band. It will be about the same as. If the gain in the low frequency range is different from the gain in the microwave band, design a matching circuit to optimize the frequency characteristics of the gain of each single-ended amplifier in the balanced amplifiers 20 and 21. From the second point, it is possible to create a wideband amplifier with a band from low frequencies to microwaves.In this case, if the cutoff frequency of the lowpass filter is set near the low cutoff frequency of the coupling degree of the coupler (: The frequency response can be relatively flat (2).

Furthermore, the amplifier of this embodiment has the same structure as a conventional multi-stage balanced amplifier, and the circuit with low-pass characteristics is, for example, as shown in FIG. A small circuit can be easily constructed by using the binding wire 32, etc.

It can be made to have almost the same dimensions as a conventional amplifier.

Note that in the explanation of figure 'f15, the resistor terminations 27 and 28 are directly connected to the isolation terminals 22 and 234, but
Resistor termination: 17, 2B as shown in Figure 7
Isolation terminal xx, 5i4= via 4, 35
May be connected. This way, at low frequencies, the resistor termination 2
7.28 does not become a loss sine, so it is not necessary to increase the gain in reducing the individual single-ended amplifiers constituting the balanced amplifier.

In addition, so far we have explained the hybrid coupler using an interdigital type as an example (2), but this can also be done by using the multistage coupler shown in Figure 4 or the combination of the low-coupling coupler shown in Figure 8 1m. (The present invention can be applied even if there are two balanced amplifiers.)

As described above, according to the present invention, it is possible to provide a high frequency amplifier having substantially the same shape and dimensions as a conventional balanced amplifier, but having wider band characteristics.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a conventional balanced amplifier, Fig. 2 is a plan view of an interdigital coupler used in the balanced amplifier shown in Fig. 1, and Fig. 3 is a plan view of a conventional interdigital coupler. Characteristic diagrams showing transfer characteristics, Figure 4 is a plan view of a conventional multistage coupler, Figure 5 is a circuit diagram showing an embodiment of the present invention, and Figure 6 is a diagram showing the low-pass characteristics of the present invention (2). 7 is a circuit diagram showing another embodiment of the present invention, and FIG. 8 is a plan view showing another example of the coupler according to the present invention. ...Single-ended type Amplifier, 5.; 25... Input terminal, 6, 1... Combiner output terminal, 8, 22. 23.
...Isolation terminal, 10,27.28...Resistor termination, 20.21...Balanced amplifier. 24...Low pass filter, 26...Output terminal, 3
4.35...cano armpit.

Claims (1)

[Claims] In a high-frequency amplifier in which two balanced amplifiers each consisting of two hybrid couplers with resistive terminations and two single-ended amplifiers are connected in cascade, the hybrid coupler is connected to the output side of the preceding stage amplifier. A high-frequency amplifier characterized in that a circuit having low-pass characteristics is inserted between the isolation terminal and the isolation terminal of a hybrid coupler of a subsequent stage amplifier for coupling.